2009 CNC Blog Archive
Swing Threading Toolholder and other Threading Aids for Manual Lathes
Threading on a manual lathe seems to be a scary process the first time around. I didn’t attempt it for my first year or two of turning, for example. Eventually, you reach a point of needing to thread something that’s too big to make sense for a tap or die, and then you just have to deal with it. I’m not going to try to attempt to explain threading on the lathe here, there are lots of good resources that do that. Personally I like the Southbend Lathe Book, which is readily available.
Rather, I’m going to talk about a couple of aids for threading that I have come across recently. It seems that the issue that really bothers people is the retraction, often complicated by the desire to thread up to a shoulder. There is a certain amount of pressure on the operator to do several things very quickly: stop the feed, retract the cutter, reverse to start the next pass, advance the cutter, restart the feed at exactly the right point on the threading dial. If you make a mistake, you can bollocks up the thread or crash your threading tool into your shoulder. I hate when that happens!
So the first aid I came across is what I will call a “Swing Threading Toolholder.” This is a cool idea from HSM and other boards. When it comes time to reverse, stop the lathe, and simply reverse. Leave the half nut locked (some shops feel this gives a more accurate thread anyway). The “swing” is because the tool is free to swing upwards when it contacts the threads moving in reverse, so it doesn’t cut on the return pass and you needn’t retract.
Here are some Swing Threading Toolholders:
John Stevenson modified a carbide threading tool with a pivot and shelf underneath…
Gary Hart made a swing threader that uses carbide inserts…
It pivots on a 1/4″ dowel pin.
That’s a fancy looking little design. I wonder if the handle locks the swing or what?
(A kindly reader has informed me this is a George Thomas design that was published in Model Engineer. The lever may be used to withdraw the cutter.)
Bogstandard’s very elegant looking version. I saw his first, so I saved it for last…
By all accounts, these Swing Threaders work really well. John Stevenson says it is the fastest thread he had ever cut.
Another manual threading aid is a system of stops on your handwheel. The Monarch 10EE’s came with such a system. There are various shopmade ways of providing something similar:
This is John Stevenson’s copy of the 10EE system…
The exploded view of the 10EE system. Note the setscrew on the right.
To engage the system, just wind the set screw in. It will engage the first of the three dogs. That gives you one rotation until the first dog engages the second, giving another rotation to engage the third for a last rotation. So you can turn the handwheel 3 rotations against the stops. The depth of cut is set by the top (compound) slide. Set the depth, crank the lower slide all the way to the stop, cut a pass, retract the lower slide to opposite stop, and traverse back for another pass. I kind of like the Swing Tooling better, but who can argue with the genius of Monarch? John has retrofitted this to some other lathe in his shop, a TOS I think?
A similar idea that engages a pin in the dial. This would only allow one turn of retraction.
Here the thread stop is flipped up to disengage it…
Spectacular Tormach Flood Enclosure
This was up on CNCZone, just gorgeous:
Separating Chips from Coolant in a Shopmade Enclosure
If you’re going to run flood coolant, an enclosure is a must to keep the mess under control and out of you shop. I keep an Idea Notebook of shopmade enclosures because at some point I’ll be tackling this chore for my IH Mill. There are lots of good ideas there. The latest one I ran across is this approach to separating the chips and the coolant seen on CNCZone:
At first I thought it was a chip conveyor…
The idea is to slow down the flow along a shallow incline so the chips can drop out through gravity. Presumably a couple of ridges would help even more with the process. He also uses the normal arrangement of de-humidier foam filters and that sort of thing, but I think the real secret is this trough. Most of these enclosures just mount a kitchen-sink drain in the bottom and pipe it straight down to the coolant reservoir. Letting gravity and slowly moving coolant (because that trough has only a shallow incline and is very wide and deep compared to the amount of coolant seems a clever move.
Ultimately the coolant winds up in this reservoir under the enclosure…
Blast Cabinet Tweaks
Blast cabinets are really handy to have in the shop (if you’ve got room, they’re not compact). The cheap ones actually work really well (I gave $60 for mine on eBay), but they have their drawbacks too. So, as any good machinist would do, we start thinking about how to “improve” the cabinet. Here was a good idea I came across on HSM:
Note the PVC with holes run along the top. This is Steve45’s idea to blow some air across the window to keep the dust away so he can see what he’s doing. The other thing that seems to help is adding a ShopVac-based dust collector. I understand even the cheap ones from Harbor Freight make a nice difference.
Lately I have also been eyeing some higher quality guns. The gun that comes with a cheap blast cabinet is serviceable, but not very slick. At some point it will wear out and I’ll look at nicer guns. A company called TP Tools has some interesting blast cabinet accessories including higher quality guns and a lot else. Their niche is air equipment of all kinds, but they specialize in blast cabinets, painting, and compressors. I found out about them after purchasing an electric compressor drain on eBay for my big Eaton compressor.
The Devilmaster Redux: Gorgeous CNC Router
If you’ve never seen the Devilmaster’s work, you must take a look. It is really outrageous. Here is his fixed gantry CNC router as pictured on CNCZone (which brought me back to Devilmaster’s delightful work):
So many tasty touches on this beauty!
Here is his watercooled PC video card, which is one of the things he likes to use his router to make:
My brother loves woodworking, and we keep talking about building a CNC router for him. I’d love to do something like this but on a much larger scale. He’d need 4′ x 4′ or maybe larger as he likes to do furniture. I keep thinking about building a fairly massive gantry out of epoxy granite too, and did a design sketch and some notes about how to go about it.
Epoxy Granite Table with Inserts…
The Master Jaw System: Turn Your 3-Jaw Chuck Into a 5C Collet Chuck
Yantra3D, from CNCZone, sent me a note today letting me know that if you liked Geoff’s Excellent Collet Chuck Alternative (see the article below), you can buy one off the shelf called The Master Jaw System. Apparently it is a “precision length” system. I assume (you know where that leads) that means that if you align the workpiece against a stop and then lock down the collet it doesn’t move. One annoying thing about 5C’s is that most collet closers pull the collet back into the taper, which of course means the length is all over the place.
Make It Easier Changing Pulleys for Machine Speed With a Bicycle Chain
Well sort of. I thought this idea from Weirdscience on HSM was pretty clever:
Bicycle chain hinge on the bottom is pure genius…
Sure beats yanking on that capacitor!
What does a first-time Mill user need?
Every now and again, a newcomer wants to know what basic tooling they should acquire. The trouble is, as a newcomer, you’re not in a good position to judge (been there, done that). So I thought it would be helpful to create a thread where experienced machinists talk about what the MINIMUM set of tooling to get started with a mill might be. By MINIMUM, we’re trying to help folks out who are on a budget, but not go crazy with it. Let’s also have a NICE TO HAVE category of the first things you’d buy after you get past MINIMUM. And, let’s assume they own no tooling whatsoever, not even a calipers. My list is below. What’s your list?
– Kurt-style vise (or a grinder vise if the mill is really small)
– T-Slot Clamping Kit
– R8 End Mill Holders
– R8 Keyless Chuck
Note: Some prefer R8 collets, and they’re definitely cheaper. I’ve always used the solid holders and like them a lot better!
Measurement & Layout
– Digital Calipers
– Sharpies (Buy a box, they’re cheap and hugely handy!)
– Calculator (Online like G-Wizard or handheld)
– Dial test indicator. Don’t get a tenths indicator to start, though you could consider 0.0005″ indicators.
– Some way to attach the DTI to your mill spindle for tramming. An Indicol or clone (available cheap!) would work great.
– Spot drills / Center drills
– Twist drills (I prefer screw machine length as they’re more rigid. I almost never use the jobbers, and most peeps will already have some of those anyway)
– Endmills: 1/8, 1/4, 1/2 in 2 flute and 4 flute. At least 2 of each size.
– We haven’t talked about how you will cut stock to size. Hopefully you have a bandsaw or chopsaw. Failing that, get a hacksaw.
– WD-40 to use as coolant. If you can, buy a spray bottle and the gallon can of it rather than the aerosol. It’s cheaper in the long run.
– Cheap chip brushes
– A decent file
NICE TO HAVE (What to buy after you have a little time with the MINIMUM)
– Make or buy some softjaws for your Kurt vise.
– 1-2-3 blocks, and eventually 2-4-6 blocks
– Edgefinder: I like the electronic kind, which can be converted to probes in Mach3 if you go CNC.
– Small Kant-Twist clamps: Tons of uses beyond clamping. They make great vise stops, for example.
– Deburring cutters. I like the zero flute style.
– Scraper-style deburring tool
– A flycutter or a face mill
– Surface plate and height gage: This one is borderline NICE TO HAVE. But I sure do use mine a lot, especially for layout when manual milling.
Must We Have a Burr When Drilling?
Lately I have seen arguments break out over whether machining will always produce burrs. The answer, so far as I can tell, is “Yes, but not always noticeable burrs.” For example, when doing my light cut/high feedrate machining with chip thinning, I see minimal burring. A fellow named TatooMike, who frequents various boards gave a great suggestion about how to eliminate burrs when drilling. He suggests creating a fixture so that the workpiece is stacked atop another piece. You’ve probably noticed when drilling stacked parts that only the bottom part in the stack gets the burr. If that bottom part is your fixture, you may have saved yourself some deburring.
The other thing I saw suggesed, but haven’t tried, is the idea that excessive burring with a twist drill is a result of plunging too fast. Certainly having the proper feeds and speeds helps, but I wonder if slowing the plunge as you near the hole exit on CNC ops wouldn’t also be helpful.
Tapping With Ye Olde Butterfly Impact Wrench
Josh from the HSM board sent me a PM this morning. He has made a real nice video on YouTube of my idea of tapping with the Butterfly Wrench:
Tapping made easy…
You need a set of Irwin’s tap wrench adapters for a socket wrench, I got mine from Enco:
It’s amazing how well these little wrenches work, and they’re dirt cheap. I have one built into my powered drawbar, one loose, and one attached as a “hand powered drawbar” to my 2nd mill:
Just reach up on top of the spindle with this and tool changes are a snap!
People worry these impact wrenches will break their taps. I haven’t broken one yet, but I’m not sure I’d use a really tiny tap in the impact wrench.
To reduce the likelihood of breaking a tap, consider the following:
– Always use tapping fluid. I like tap magic and keep a can near the vise where most of my tapping occurs. I apply it liberally to the tap. Josh is spraying on some WD-40, which ought to work too.
– There is a built-in regulator on the wrench. Turn it down for smaller taps so you don’t have full torque. These little wrenches don’t have a ton of torque anyway. You can see in Josh’s video his wrench really slowing down when it starts to cut.
– Use sharp taps. Josh is using a hardware store tap. They work, but there are better taps to be had. Do yourself a favor and get some form taps and some spiral taps for the hardware sizes you use most often in your shop. Wait until they go on sale and buy a few in each size. Be sure to get quality US made taps. Try them by hand first and you’ll be amazed at how much less pressure is needed to tap a hole. The spiral taps extract the chips right up out of the hole very nicely. They designed so you don’t have to keep reversing to break the chips, just keep on going. Form taps require a little more effort. They don’t make a chip at all, they cold form the metal to produce a thread. I read on one manufacturer’s site that they are 4x stronger (and therefore less likely to break) than cutting taps. I prefer form taps in aluminum, but there is a limit to how hard a material they will cut. Mild steel at best.
– Make sure your’ve got the right-sized hole! My G-Wizard Machinist’s Calculator will figure that out for you based on what % thread you want to cut. If you’re at all worried, choose a lower % of threads. The threads won’t be as strong, but the bigger hole will make it easier to tap.
– It really matters to thread along the axis of the hole. That means the tap has to go in straight. There are lots of ways to ensure this, but a moment of inattention is all it takes to blow it. Once you have cut threads at an angle, it’s too late. The smaller the tap, the more sensitive they will be. For real small taps, I use a piloted tap wrench in a drill press, a milling machine, or my lathe tailstock.
Eventually, I am going to build a tapping arm, which makes it easy to tap holes that are perfectly vertical:
Commercial tapping arms use air drills. They’re available, but you want one with a low rpm and easily reversible with your thumb. So far I haven’t seen one like that for less than about $500. So I use my Butterfly Impact Wrench which cost less than $25. Try it, you’ll like it!
CNCCookbook Gets a New Bandsaw
It has been a busy weekend for the CNCCookbook.
I have had the ubiquitous small Harbor Freight horizontal bandsaw for a long time. I found I use it more often in vertical mode than horizontal once I made a little table for it. The little saw has been handy, but it’s just too small for many projects. A lot of stock and machining time can be saved by using a bandsaw to cut things closer to size. A rule of thumb is to get within about 0.100″ of your milled cut. So I’ve been on the lookout for a bigger saw for some time. I wanted something local and good sized.
The new (to me) saw is a Delta Rockwell 18″, which is quite a bit bigger!
It looks gorgeous and new with only has 500 hours of running time on its Hobbs meter:
This saw looks identical to the saw we had in my high school shop class, although it is much newer. Nice to be able to put a piece of American Iron still in good shape into my shop. This machine is capable of cutting either wood or steel, so it has a nice broad range of speeds that include a 2 speed Lo-Hi gearbox and a variable pitch pulley to change speeds within the range.
Now I will still need to come up with some 3 phase power before I can fire it up!
Finished a New Coolant Mister Last Weekend
But I’m just now getting the article written and photos posted. The full details are on the project page for the mister. It looks like this:
Originally I was going to build the mist nozzle/mixer too, but I got an eBay deal on a Noga unit…
Mitutoyo 190: Swiss Army Knife of Calipers?
Saw this on PM after a kind soul brought it to my attention via PM:
Wouldn’t work for me, being a child of the digital rather than the vernier age, but it sure is cool!
I’m wondering if there isn’t a project here somewhere to adapt a standard digital caliper to do all these tricks.
Glenn Wegman’s Indicator Holder
I really liked Glenn Wegman’s indicator holder because it has a knurled wheel to make easy to turn the spindle while using it:
How Many Plates, Er CNC Machines, Can You Keep Running at the Same Time?
I’ve seen numbers up to maybe 4 or 5 machines. Load one up, hit Cycle Start, go to the next one, rinse repeat. If you can keep 4 or 5 machines going at the same time, that’s hot stuff. Most shops think about their business as though the machines are “hourly income”. A machine makes say $75/hour. Keep 4 of them going with one operator and that’s $300/hour.
But with so much going on, it’s easy to lose some minutes here and there. You walk away and get focused on something, the machine finishes, and you don’t notice. What to do?
I liked the note in this PM thread about a guy named “Ox” who started clipping egg timers on to his clothing. One for each machine. Start the timer when you hit cycle start. When it beeps, it’s time to go back to check on the machine.
Single-Edged Razor Blade Line Pivot
Nice Rigidity Bump Up for Small Sieg Mills
Dougal over on CNCZone has the right idea. He bolted a nice piece of channel to the back of his Sieg X2’s column. It even looks factory:
Now why the heck doesn’t the factory do that?
The Case for Parabolic Drills and Some New G-Wizard Functionality
It is always hard to drill deep holes, where deep is defined by a hole that is many diameters of the drill bit deep. I recently came across a question on CNCZone that started me doing some research on the topic of parabolic drills. Parabolic-style drills were developed in the early 1980s. They use a heavier web to create higher rigidity and increased flute area for chip removal on deep-hole drilling operations.
Precision Twist Drill has a nice discussion on their site of how to vary feeds and speeds to accomodate deep holes when using regular and parabolic twist drills. I was so taken by the CNCZoner’s question and that nice discussion that I wound up adding a bunch of functionality to my G-Wizard Machinist’s Calculator.
The new functionality is both to implement the feeds and speeds adjustments recommended by Precision Twist for deep holes, but also to give recommendations based on the hole depth. For example, it suggests when you need to use a peck drilling cycle (where you drill down a little ways and then retract to clear chips) as well as when you should be considering a parabolic bit instead of a regular twist drill.
The question the CNCZoner raised was what feeds and speeds to use when drilling a 0.201″ hole 3.5″ deep. That’s over 17x the diameter in depth, so a parabolic drill is definitely called for!
Here is what G-Wizard shows when you enter those parameters:
Note the box for Parabolic is checked, which tells G-Wizard we want to use a parabolic drill. Also, it is recommending a peck drilling cycle (DUH!) for this 17.412x Diameter hole depth. If we enter a less severe hole depth, 0.2″, it recommends 3800 rpm and a feed of 16.85, whereas you can see from the diagram it has compensated for hole depth and slowed down both the feeds and speeds. The feed is slowed as a result of the spindle rpm. Parabolics don’t need further slowing. A regular twist drill would also get feedrate reduction on top of that.
More Clamping Tricks
Ray Behner’s clamping trick spawned some more good ideas:
I’m going to have to CNC a big table clamp like that one on the right!
Of course the table clamps can be turned on their sides to accomplish the job in the bandsaw vise!
No Trick, Here’s a Treat: Bandsaw Vise Trick
Saw this on PM from Ray Behner:
Coolant Collar Idea Notebook
Speaking of Idea Notebooks, I’ve added a new one to track ideas for Coolant Collars:
Sturz Milling and Other High Tech Milling Tricks
I wanted to add the calculations for ball nose end mill compensation to my G-Wizard Feeds and Speeds Calculator, so I got to researching ballnose cutter compensation calculations, scallop height calculations, and all that sort of thing. Somewhere along that way, I came across references to “Sturz Milling.” This Ingersoll treatise on their indexable ballnose cutters had some of the best data.
The notion here is that the speed of a ballnose cutter varies depending on your depth of cut. If you have very little depth of cut relative to the diameter of the ball, you actually have a much different effective tool diameter. You’ll need to speed up your rpm’s to take into account that effective diameter. For example, an 0.100″ depth of cut on a 1/2″ ballnose endmill actually uses an 0.400″ effective tool diameter, not the 1/2″ you may have thought. G-Wizard figures out all of that stuff for you just by checking a box.
But what is this “Sturz Milling?” Essentially, it is the idea of tilting the cutter relative to the normal to the surface being machined to keep the very tip from cutting. That tip is a “dead spot” on the cutter because it isn’t moving very fast. Being able to easily do these tilts is a big advantage for a 5-axis machine doing 3D profiling. However, even on a 3D mill, you can try to orient the workpiece so the cutter is never perpendicular to the surface you need to 3D profile. For some parts, this may make a big difference both in terms of how fast you can machine and for the surface finish.
The Ingersoll pamphlet has a few other interesting ideas. For example, the suggest reduce the feedrate as an indexable cutter enters the cut. The reason is that until you reach full engagement, not all the inserts are cutting. There is definitely a noticeable roughness I’ve seen at the beginning and end of a pass with the facemill, for example. It would be interesting to fool with the feedrates there to see if it could be smoothed out a bit.
They also suggest slowing down in a corner by 50%, but not dwelling. Corners are definitely an area where there can be a lot higher engagement, so slowing down there can be helpful. Conversely, if you have created a g-code program that works great through the corners, you’re probably going too slow on the straight paths!
Another great Ingersoll resource is this tech pamphlet on milling cutters. It’s got all sorts of great information on chip thinning, lead angles, and other useful data. For example, they discuss the impact of lead angle on milling cutters. Consider two face mills. One has a 90 design and can be used to create square shoulders. The other has a 45 degree design. Why would you ever want the 45 degree face mill? Because the lead angle changes the performance of the cutter in some interesting ways. Consider the geometry:
The 45 degree face mill is on the left, and the 90 degree is on the right. You can see from the diagram that because of the angle, the equivalent depth of cut is much less for the 45 degree mill. In fact, you have to multiply the feed by 1.4 to get the same depth of cut, which corresponds to the chip load. So you can feed a 45 degree face mill 1.4x as fast as a 90 degree face mill. Whoa! It turns out your surface finish with the 45 degree face mill is often a lot nicer as well.
As you can imagine, similar calculations can be done for face mills that have circular inserts. These are often called “button cutters” although some manufacturers call them “toroidal cutters” too.
Have you heard of “high feed” inserts or cutters? I like to think of them as combining some of the best of both lead angle and button cutter capabilities. Imagine an insert that has radiused corners with a big radius (that’s the button cutter) and further, imagine the insert is mounted at an angle so that that straight edges connecting those corners generate a nice lead angle effect too.
Star Trek in the Machine Shop: Tricorder or Phaser?
Yes, I’ll admit, I’m a Trekkie. That’s getting to date me I think. What’s this all about?
Check out these devices:
The sorter performs a function not unlike Mr Spock’s Tricorder (although it looks to me more like a Phaser!). Specifically, you point it at a piece of metal alloy, pull the trigger, and it tells you what the alloy is. How does it work? It’s an X-ray spectrometer. It basically zaps the metal with an X-ray and then looks to see what the metal does in response.
Manufacturers use them to make sure alloys on projects where the material has to be “right” are as specified. It’s all part of a manufacturing process called PMI for “Positive Material Identification.”
Servo Drive Reviews and a Big Drive for Your Spindle
Macona on the HSM board recently called my attention to this review page for servo drives done by TheCubeStudio. That’s a very cool review page, nice to see all the pros and cons from someone that actually tried to get all of the drives working. I learned about a couple of drives I would not want to try my own money on!
Because of the reviews, I became aware of the reviewer’s favorite drives which are made by www.cncdrive.com out of Hungary. They look like extremely nice drives. I am always on the lookout for larger drives, on the off-chance I want to use one for the spindle of a CNC. Big drives are often expensive and not available to the low end market unless via the surplus and used markets such as eBay. It’s very handy to have a servo driving your spindle for such things as positioning for a tool changer (CAT40 and many other tapers have “drive ears” that have to be lined up), or in the case of a lathe, indexing for live tooling, for example to drill a bolt circle on a flange.
CNCDrive’s largest drive is called the Dugong, and it can handle 160V at 35 amps. With a 20% safety factor, that would be about 4.5 KW = 6 HP. That’s more than enough for a lot of spindle purposes. They cost less than $200, which seems very reasonable. The other thing I like about these drives is they connect via USB to allow tuning with software, so no need for an oscilloscope.
I may have to try one at some point!
The other cool device from Macona’s post is the Teensy Arduino USB controller. These little boards are a complete PC on a chip with the ability to control signals such as relays and so forth. Lots of possibilities for such an easy-to-program and inexpensive device. The thread talks about using steppers or servos to automate a surface grinder that lacked a power feed, and that would be an excellent place to start.
Chuck-In-A-Vise and Other Wisdom of the Widgitmaster
I liked the Fidgeting Widgitmaster’s little fixture to keep a small 3-jaw chuck handy in your Kurt vise:
I guess you can leave the key in the lathe chuck when it’s on the mill!
The chuck is mounted on a steel block so it’s easy to clamp or just drop into the vise. It’d be easy to use on a drill press or rotary table too I bet! It would even be handy just for the bench.
I need to make one up for my own shop.
Milling Quite a Compound Angle
Some machines have interesting capabilities:
Organize Your Lathe Tooling: New Idea Notebook
I came across a bunch of new ideas for how to organize your lathe tooling, so I created a page to show it off. Idea Notebooks are what I call pages that have lots of ideas for how to do a particular project. You can see the list of them on the Cookbook page.
Here is a typical sample from the Lathe Tooling Organization page:
Widget Squares a Block (And Builds a Cool CNC Router)
I just got done looking through the thread on one of the Widgitmaster’s latest creations on CNCZone. He’s busy converting one of his earlier 24×24″ routers from v-groove pulleys to round linear rails. Keep an eye on it if you like the machine that results as he will be selling it on eBay.
I always learn a thing or two watching Eric’s meticulously documented projects, and I like to share those learnings here.
Here are some highlights:
Got a big workpiece? Make yourself a rig like this. Aluminum softjaws span 2 vises. Widget is tramming the vises with his DTI against the jaw…
Yes, it’s aluminum, and yes that’s a 4 flute endmill. Why? Because it isn’t a pocket, it’s peripheral, so the chips can easily get out of the way. And, because you can feed a 4 flute twice as fast for a given spindle speed. Nicer surface finish too, in my experience…
Two things to note while squaring this block. First, check out the Starrett vise hold downs on either side of the block in the vise. Need to get a set of those myself! Second, check out the great big fly cutter he is using…
Having changed leadscrews, Widget needs to rebuild the hold to fit the new leadscrew. To do that, he wants to shrink fit that plug into the hole and then machine the plug for the new mounting…
The plug, 0.0005″ oversized, goes into the ice box, and the assembly is heated with the OxyAcetylene torch. Drop the plug in and tap it with the sledge and it is going nowhere!
It might as well all be one piece of aluminum…
Do you have a problem with larger twist drills twisting in your chucks and getting scarred up? I do. Silver and Demings are the biggest, but they all share a common shank size, so you can stick them into an endmill holder. A little Weldon shank action on that big bit and you’d really be able to lock it in place in the holder…
Boring a really deep hole, how do you minize the chatter?
Take a large diameter lathe boring bar, one with a shank that would never fit your boring head. Turn down the shank until it does fit the head, like a Silver and Deming twist drill bit. Smart!
Indicating the slitting saw in with some space blocks so the middle of the saw cut is just where it needs to be relative to the top of workpiece. Widget suggests plunging the saw straight in rather than starting from the side when cutting because the hole will keep the saw centered instead of pulling it off axis…
Lots of goodness here: Outside vise jaws will be used to clamp a big workpiece. Not only are the outside, but they are wider than the vise. Widget is milling a step into them to use instead of parallels (how will you get parallels in there anyway), and since the steps are milled, they’re prefectly trammed. Lastly, check the 1-2-3 blocks and drill rod. Drill rod keeps from overconstraining the setup (i.e. makes it more accurate) and having them in there loads the vise as though there is a workpiece in there…
This gantry router uses 2 vertical arms. Widget rough saws the arms on the bandsaw, but all edges will need to be milled square…
Widget had been thinking ahead. He has two holes for dowel pins that in the material that will be milled away. The dowel pins let him line up the milling pass perfectly because they align the workpieces against the square mill table edge…
Having clamped the workpiece using the dowel pins for alignment, Widget removed the pins and made his milling pass. Now he has a nice square edge in exactly the right place!
Here’s What We’re Building. Looking Good!
Clever Shopmade Bore Measuring Tools
Nice thread on HMEM about these:
The fixed jaw slides along the shaft. The movable jaw is the indicator’s probe…
And another from the same thread by John Stevenson:
Finally, this beauty is evidently a design published in Model Engineer magazine in the 1980s:
Set to maximum bore diameter range…
Set to minimum diameter range…
These are all relative measuring devices. They need calibration against some standard, though a micrometer should work easily enough. They can then tell you how the bore compares to the standard using the dial indicators.
Offset Relative to the Machine, Not the Part
I was reading a thread on Practical Machinist this evening that jogged some thoughts loose that had been rattling around, but which I had not gotten into a coherent state:
On a CNC machine, you want to set things up as much as possible so everything is relative to your machine, not your part.
I can tell you from experience that this isn’t how newcomers think about it, but it makes a lot of sense if you’re trying to do anything on a production basis versus a one off. Most of the time I’ve been coming in and touching off some feature of the block I start from, for example touching off the top of the part to establish the Z = 0.0 datum. Typically, I would slap a chunk of material in the vise, touch off by eye (close enough) to start squaring the piece, get it squared, and then wind up touching off again with a Z-axis presetter before I started my CNC job.
If you’re setting up relative to a part, you’ve got to indicate the machine, touch off, or otherwise let the machine know where the part is for each and every part. But if you’re set up relative to the machine, that’s not a problem because your machine isn’t going to move around–or at least it had better not!
My friend Pete in Hawaii takes this one step further. He has established a reference 0, 0, 0 point relative to the vise jaws in his mill. He does all of his CAD/CAM work with the expectation of that reference point. This way, he drops a block into the vise, hits the green button, and away it goes. Multiple vises? You’ve got offsets to deal with that too. Likewise if you run a fixture plate, it would seem advantageous to get out your probe and log the coordinates of all the salient features of the fixture plate. For fixtures, a lot of shops put a feature on the feature that they can dial in on once the fixture is installed on their mill. I’ve even seen this done on soft jaws for vises, which are not repeatable when you swap them on a Kurt vise. A precision hole is one easy feature to dial in on for vise jaws.
What about dealing with variations in rough workpieces? Set some standards. Machine Shop Trade Secrets suggests you bandsaw workpieces to within a 1/10 of an inch. If you’re running production, that’s probably not a bad figure to adhere to. Use a stop on your saw if you’re manually feeding to make sure each piece comes out close enough. A variation of 1/10 of an inch is nothing to a face mill if you’re going to surface that edge before starting to machine. If you’re on a smaller machine where it really matters, set it up to take 1/2 of that 1/10th out (50 thousandths) on the first surfacing pass. If you’re really accurate to 1/10, you’ll be pretty close to that 50 thou cut or it’ll be less. If your parts are 2D contoured with a laser or water jet before they go on the CNC, they should be well within these tolerances.
A Poor Man’s QCTP Dovetails
Most of the thinking on the thread has to do with making the dovetail in several parts ala this drawing by Brian Rupnow:
Note the use of dowel pins to accurately locate the femail dovetails. Another approach might be to machine a shoulder they could position against. Some locating is needed because bolts are not for locating unless they have shoulders so they can act like the dowel pins.
Atty showed a picture of a QCTP holder made the way Brian suggests and sure enough it came out pretty nicely:
No dowel pins, but he says it works well. For holders, especially, I think a machined slot could provide the locating as well as a little more rigidity.
Lastly, Paul Alciatore presented this very slick alternative to the dovetail approach:
This design would be extremely easy to make. It clamps against the flat of the toolpost. I assume height could be adjusted with a setscrew bearing against the holder flange at the bottom. Generally, it looks more solid to my eye than the Aloris-style.
First There Was “Mini-Me”. Now, Say Hello to “Mini-Haas”. Guldberg’s KX-3 Enclosure and Slant Bed Lathe Projects
Great build thread by a Danish man named Guldberg over on CNCZone. It’s a CNC’d Sieg KX-3 with an extremely nice enclosure:
Note the choice of colors matches Haas pretty well!
Guldberg is also building a slant bed CNC lathe from scratch:
3D Model of the lathe…
Back from Uncle’s machine shop. Construction is welded plate. Linear ways. Surfaces were trued on a big CNC horizontal mill.
Base is polymer concrete filled like my mill…
3-Jaw clamped to mill to machine the locking plates for the lathe’s tool turret…
Here is the turret. Air cylinder unlocks the turret by spreading the teeth. A stepper rotates the next tool into position. Belleville’s apply pressure to lock the teeth…
Some of the projects you see out there are just amazing. Guldberg is definitely doing first rate work and having a lot of fun at it. He’s got me thinking about an enclosure for my IH mill now. Sure would be nice to keep the chips up off the floor!
More Notes on Indexable Tooling
There is a massive and typically inflammatory thread about indexable tooling and small machines over on the HSM board. If you can get through all the posturing (maybe just look at the pictures?), there is some good information there. I summarized it in a post as follows:
The ANSI standard differs with a lot of what the catalog charts have to say:
The catalogs and the posters here attribute a lot more to those 4 letters in an insert designation than I can read into that spec which seems a lot more related to making sure inserts are interchangeable with their holders than anything else. For all the pages here, there are really very few points being made that matter for making chips:
1. Positive rake requires less cutting force and is generally better for lighter machines. In fact, positive rakes are taking over from negative even for heavier machines in many cases because the geometry cuts better. You can see that reading through the PM board to see what those guys use/recommend. Negative rake is principally useful for durability, but as the positives get better at interrupted and other “difficult” conditions, why bother with negative?
2. The meaning of the various letters in an insert designation is pretty prosaic. Some things we can determine from it but most we can’t. We don’t know the rake unless we factor in the toolholder and the top surface of the insert. Those two are actually not called out very well by ANSI. Therefore, we have to understand our toolholders and the meaning of positive rake and visualize what will happen with a particular insert. Those “sharp” inserts are clearly very much going to have positive rake. Many other inserts it isn’t so clear.
3. Since you can’t really tell from just the 4 ANSI letters what’s going on, you’d better have one or more of the following in hand before buying the insert (unless you just want to experiment):
– Full ID on the insert so you can go consult the manufacturer’s catalogs. This is often hard on eBay.
– A big picture of the insert and enough practical knowledge (more than enough in this thread) to guess how it will cut.
– A solid recommendation for the insert from someone doing similar work on a similar machine.
– Help from a rep picking out your inserts. Clearly YMMV depending on how good the rep is. This is why peeps like the “Exkenna” guy over on PM so much, or Frank Mari. Their advice has prooved out.
Everything else is a crapshoot and can be extremely frustrating.
Just as an example, not long ago the CCGT inserts were the ticket for smaller lathes. Peeps thought the “G” meant “Sharp”, but it was only the tolerance. It wasn’t long before manufacturers were selling “G”‘s that weren’t sharp because there was demand to pay the higher price. Then I started seeing CCMT’s that were Sharp. The whole ANSI business ceased being a useful determiner of anything other than whether the insert would fit my toolholders. Hence the 4 criteria above.
4. The idea of a lathe “too lightweight” for carbide is an interesting one. A small Southbend will clearly handle carbide. My Lathemaster 9×30 does too. The ubiquitous 9×20 is noticeably less rigid than these, but with the common mods, seems like it would work. What then is “too lightweight”? Unimats? 7×14’s? For the hobbyist, carbide is a matter of personal taste more than anything. Do you want to spend your time trying to understand the minutiae of insert selection (feels like stamp collecting sometimes), or grinding HSS tools? Either takes away from making chips, but I like my carbides though I also do some HSS.
Last point: Be careful if you have an indexable tooling fetish as I do not to accumulate tools that use too many different insert types, or inserts of exotic design. It’s just too hard to keep up with it all. Hence all my mill tooling uses APKT (or equivalent) and all my lathe tooling except the boring bars and parting tool uses CCMT.
Apparently cheap toolholders look like such a deal until you’re paying $10 and up per insert on a facemill with 7 inserts. Ouch!
Powered Drawbar Engineering Challenges
Powered drawbars are extremely handy things. They make tool changes a snap. I can vouch personally for how great the one I made from an impact wrench is. There are basically two versions. The first, and most common, is like my impact wrench version. It literally simulates the normal operation of an R8 drawbar, and just automates the tightening and loosening along with a little “gentle persuasion” ala the mallet tap that comes in the form of the impact wrenches hammering as well as downward pressure from the air cylinder.
The second version is less commonly seen, and attempts to function more like powered drawbars in commercial VMC’s. This one simply uses a stack of Bellville washers to tension the drawbar, and an air cylinder to release that tension for a tool change. The tool is held in an R8 collet that stays quasi-permanently attached to the drawbar. When it is pulled into the taper, it tightens. When pushed out, it releases. This system is a little simpler that the impact wrench in its basic form, and gives a faster release cycle. Hoss built one for his X2 mill:
As you can see from the video, it works really well and is very slick. A lot of folks, having seen this style from Hoss, decided to build them for larger mills. This is where the problems start. The X2 doesn’t use a lot of horsepower. Larger mills like Bridgeports and RF-42’s like my Industrial Hobbies, can have considerably more horsepower. Let’s say up to about 3 HP. With larger tooling and more aggressive cutting, there have been problems with the tooling pulling out of the collet. The hobby crowd has basically decided this is just a matter of applying more drawbar force, but there is more at work here than meets the eye.
Consider that the numerous folks who have manufactured R8 powered drawbar systems would probably love to have a purely pneumatic system so they can reduce their costs, but for the most part, such systems are unavailable. Did they all just fail to build one with strong enough air cylinder and linkage. Not likely.
If we take a look at one of the few systems that did see the light of day, the Mach1 system, there are some interesting learnings to be had. They say their system only uses a 600lb die spring, for example. That’s hardly any force. There are reports of tools slipping even with 2500 lbs of pull force. The builder, Scott (Poppabear), comments in that thread about his ATC project for the Tormach milling machine. He tried 2500lbs, and could not take a 1″ axial cut with a 3/8″ cutter without it pulling out. Ultimately Scott decided the project was not feasible.
Is it really just a matter of more force on the drawbar? What if Scott had used 4000lb? Color me skeptical. Drawbar tensions on machines designed for ATC’s, such as CAT40, are typically under 4000lb. BTW, these huge tensions need to be applied in such a way that the force is not transferred to your precision spindle bearings with potentially disasterous results. Ray L. did a great job on that with his design.
Why is the R8 taper so problematic? In looking over the Mach1, I figured out the secret: there are really two issues to consider. First is locking the tool holder to the mill. That’s going to be a function of the surface area of the R8 taper and the pull force. I am not too surprised that 600 lbs suffices for that force, even with quite a lot of “work” being done by the spindle.
But there is a second force, and the way it works is hugely counterproductive to the first. That second force is the squeeze on a collet to hold the tool. It doesn’t exist with solid tool holders, and it is the reason the Mach1 system uses a special R8 collet closer. Note that Mach1 can also use solid R8 tooling. The special collet closer serves 3 purposes:
1. It’s threaded cap compresses the collet on the tool with a lot more than 600lbs of force. I have read somewhere that 5C collets use 1500lbs of force, BTW.
2. It creates a reference surface to preserve the Z repeatability against the spindle nose. This gives the Mach1 system the equivalent of the Tormach Tooling System. Note that solid holders are repeatable already to a few tenths. I’ve measured that myself before.
3. This is really the big secret that tells why the Mach1 system works with only 600lbs of retention. That special collet holder creates a new, more precise, and more rigid R8 male taper. You can see this clearly from the patent illustration:
Patent illustration showing how the collet closer creates a new R8 male taper: #26
Why is this new male taper so important? Because the deformation of the collet as it locks down on the tool really interferes with its ability to make good contact with the R8 taper. If you think of bluing tapers, there is no way in heck that there is much precision in that interface. So now the drawbar force must not only provide sufficient clamping, but it must also combat the reduced surface area and hence friction of the collet in the taper. The Mach1 system avoids all of that.
Folks get started on these air-cylinder only systems because they seem simpler than an impact wrench system. But they’re really not unless you’re prepared to live with a huge amount of drawbar tension, and even then I wonder how well they are going to work with a facemill or a large silver and deming bit. People keep saying that this has been tried over and over, and it has. The drawbar manufacturers would love a simpler cheaper mechanism, if only one would work. Yet they keep shipping impact wrench based systems for R8, or special patented tricks like Mach1.
What I will tell you is that a rookie machinist can build an impact wrench system in an afternoon and it won’t suffer from any of these problems. It can be completely automated for use in an ATC if desired. It’s simpler and cheaper. Your biggest challenge for the ATC is that you’ll be using solid R8 holders which don’t have a standard interface for the ATC carousel. That’s no big deal. You’ll need to fab some collars for the tooling that serves that purpose. Meanwhile, you will be saving a fortune on TTS holders and you’ll have a more reliable and rigid system to boot. Don’t take my word for it. Look at what industry does, and look at how many have tried and failed to produce an air cylinder-only system. Note that this only applies to larger mills. Let’s say mills with more than 1HP.
APET is to APKT as CCGT is to CCMT: Sharp Milling Inserts for Aluminum
I’ve written quite a bit about how to find the right carbide inserts for small lathes, but not much about indexable milling tools and inserts for small mills. Recently I bought a new Iscar face mill that uses APKT-style inserts:
It’s a little 2″ face mill, which is about right for the size mill I have. I had been using a Lovejoy facemill, but it uses these SPEX inserts that I’ve only ever seen used with Lovejoy tooling, so they’re expensive. I also have a little Iscar Helimill 5/8″ diameter indexable endmill that I really love. It uses APKT inserts and I had heard good things about these inserts in a lot of places such as the PM boards. So, I went looking for a deal on eBay and eventually bought another Iscar mill.
Along the way, I discovered there is an insert type called APET that is a super sharp aluminum cutting insert that fits any APKT cutter. Cool!
Here’s what the two inserts look like side by side:
APKT on the left, APET on the right…
The APET is specifically designed for aluminum and has a sharper edge. I haven’t had a chance to try the new face mill yet. I’m waiting on an R8 shanked arbor for it, as well as the right project. Full details when I get to try making some chips. If it performs nearly as well as the little indexable end mill, it’ll be great.
For curiousity’s sake, here is a tool shape recommended for a fly cutter on HSM:
The shape is not unlike the APKT…
The shape is not unlike the APKT. Perhaps these inserts would make for good fly cutting!
Crazy Trochoidal Toolpath Lets Router Cut Steel at 120 IPM
For all those who are skeptical about those crazy toolpaths where the cutter never turns a corner and so can go much faster (see my post below on cutter engagement for more), check out this CNCZone video of a router cutting through steel at up to 120IPM:
Normal these little routers barely have the rigidity for aluminum, let alone steel. Look at it go!
Cutter Engagement: What It Is And Why It Matters
I’ve gotten interested in understanding more about CNC toolpaths lately, and one of the most interesting topics is cutter engagement. Cutter engagement is the fraction of your cutter that is actually doing any cutting. It turns out that this can change quite a lot as your cutter travels through most toolpaths. In particular, it gets markedly worse in corners. This diagram will illustrate:
Cutter Engagement: Blue = Material left behind, Purple = Material being removed by toolpath, Red = Cutters in two stages of engagement
The cutter is moving right to left through a corner as the arrow shows. I’ve captured the cutter engagement at two positions in red. Note that when moving along a straight wall the cutter has a 90 degree engagement, but when it is buried in the corner the engagement is 180 degrees. That means the cutter suddenly has to work twice as hard when it hits the corner. I’ve shown a radial depth of cut of 1/2 the cutter diameter, but the same principle applies (albeit the angles will be less) with less extreme depths of cut. Any time we go through a corner like this, our cutter engagement increases.
What does that mean for your speed of machining? Well, to put it simply, something has to give. Normally we run the same feedrate throughout the entire toolpath. Yet the cutter works twice as hard in the corners. So that means we either run a feedrate that is slow enough to do the corners well, and we shortchange the long straights, or we run a feedrate that is fast enough for the straights, but it is way too fast for the corners. In the latter case we get chatter, lousy tool wear, or worse a broken cutter.
Most of the time, we therefore opt for the former. Most all of the recommendations we get from the cutter manufacturer for feeds and speeds assume we will run a constant feedrate and go crashing into corners, so they’re conservative relative to the straight line performance the cutter could deliver.
“Ah ha,” says the clever machinist. We just need to vary the feedrate based on the engagement angle and we can optimize for faster machining. Yep, that will absolutely work. In fact, it would be pretty straightforward to hand tweak the feedrate on the corners for simple toolpaths. It’s tedious work this hand tweaking, but you’ll definitely speed up the program. Lots of CAM programs have an option to vary the feedrate automatically as well. How much can we tweak the feedrate? Well, from the illustration, a right angle (90 degree) corner has twice the engagement, so in theory, we can run that corner at the cutter’s recommended feeds and speeds, and double the feedrate for the straightline. In practice I would not be so bold, probably opting for more like a 50-75% increase in feedrate on the straight lines. You’ll have to try it out and be aware that some cutter breakage is likely while you sort out what works for your particular combination.
Varying the feedrate works, but that is considered Old School these days for a variety of reasons. One of the more obvious is that you’ll be able to visible see the different feedrates in the surface finish.
If you don’t want to vary feedrate, the latest thinking is that you need to create toolpaths that don’t turn corners. What? How is that possible? What if I need a square corner in the pocket I’m cutting?
Don’t get me wrong, eventually the cutter will have to follow that corner, but we can do everything in our power to avoid it except where we absolutely must, and then we can do so very gingerly. Lots of approaches have been tried and they’re computed by CAM programs in lots of different ways, but in general, the produce a series of arc-like cuts instead of straight line cuts. Imagine something like this:
Imagine the tool following these circular paths as it converges into the lower left corner. A little clean up pass will be need along the edge of the bound to pick off the triangular waste pieces between the arcs, but in general, we’ve cut a corner with fairly constant corner engagement.
This can be coded up by hand for simple situations. Cutting a rectangular pocket, for example, or a rectangular slot. The results can be pretty amazing. Check out this slot cutting program Geof from CNCZone wrote:
You can see the tool moving in circles as it slices through the slot. The cutter is a 1/2″ five flute running at 6000 rpm, 1.24″ deep cutting a 3/4″ wide slot through 1″ hot rolled with a radial depth of cut (stepover) of 0.025″. My favorite speed and feed calculator, MEPro, would have suggested 2498 rpm and about 35 IPM, and Geof is able to run 2.5x the spindle speed and over 4x the feedrate!
There is more going on here than meets the eye. I won’t bore you with the math, but I have a spreadsheet that calculates the cutter engagement given the diameter of the circle (3/4″ for Geof’s program), cutter diameter (0.500″) and depth of cut (0.025″). In this case, Geof is getting about 23% engagement. It looks like there is a lot of wasted motion on that cutter on the backside of the circle where it isn’t cutting, but this motion serves a useful purpose. The cutter is only engaged 23% when cutting. But, it is not even 23% engaged for the whole of the circle. The numbers aren’t exactly right, but pretty close if we assume we get the 23% engagement on the front cutting half. That means we have a duty cycle of 1/2 times 23% or an effective 12% engagement. It isn’t 12% from the standpoint of cutting force, that’s why I refer to it as a duty cycle. Rather, it is 12% from the standpoint of cooling the cutter. So we spend 88% of each loop cutting air to cool the cutter and only 12% effectively cutting.
That cooling is less important with aluminum, but vitally important when cutting steel, which is what Geof is doing.
The latest CAM programs all have toolpaths that are designed to work this way for arbitrarily shaped pockets and in 3D. Looking at how much more performance Geof got on his simple slot cutting, you can imagine where such CAM programs can radically reduce your machining time.
Personalizing my Mach3 Screenset for the Mill
I’ve been eyeballing ger21’s “Aqua” screen set for quite a little while. I even loaded it on my home office PC to play with so I could see whether I’d like it well enough to start using it. There are a lot of things I like better about the screen set than the default 1024.set that comes with Mach3:
– It’s got a crisper, more modern look.
– It makes better use of screen real estate, has a better layout, and saves steps on some things (like Wizard selection).
– It looks ideal for use with the touch screen I’ll eventually set up.
However, it was missing a feature or two I really coveted. Most importantly, it was missing the ability to cycle through a list of jog increments. So I set about customizing it. Read more on my page about the project.
R8 Toolholder Repeatability and Automatic Toolchangers
One of the issues facing every CNC mill user is telling the CNC software where the end of each tool is. They vary by length of tool. Worse, sometimes they can vary each time a tool is inserted in the machine, even when it is the same tool. If you’re plagued with the latter, you have to remeasure tool length every time the tool is changed. What a pain!
Most “professional” CNC machines use spindle tapers that eliminate this problem for you. A CAT40 goes into the machine the same way each and every time no matter what. Your worst challenge is having a chip get caught between spindle and toolholder, or perhaps having the wrong drawbar tension. Unfortunately, the R8 taper has a reputation for not being so accurate.
One answer to the R8 problem is to use a tooling system that indexes off the spindle nose for repeatability. Companies like Tormach sell these tooling systems, and sometimes people make their own equivalents as well. These systems have a round shank that goes into an R8 collet. They have a collar with a shoulder that provides a positive stop against the spindle nose. Release the pressure on the R8 collet, shove a toolholder up until the collar makes contact with the spindle nose, tighten the collet again, and you have repeatability in the Z-axis. You can record the tool offset for that toolholder and it’ll be the same the next time you plug the tool in. Much time measuring tool heights is saved as a result!
That’s all fine and well when using R8 collets, but I’ve never especially liked them anyway. I prefer endmill holders and collet chucks. These have a solid R8 shank, so I have a hard time believing their repeatability is significantly less than a system like Tormach’s. It’s easy to see why collets don’t repeat– they’re pulled up into the taper a variable amount until they lock down on whatever shank they’re gripping. Differences in shank diameter lead to different Z-lengths. I see this all the time when I use my 5C collets on my lathe.
But a solid endmill holder or collet chuck has no “give”. Can’t you tighten it up in the taper and expect the same result each time?
Of course I had to try the experiment. So I ran downstairs to the shop, grabbed my HF butterfly impact wrench (I just use it handheld on the CNC mill), and my Z-axis toolsetter:
Checking tool Z-axis height. Mill is covered in chips because I was just making parts…
I established a baseline, and then I replaced the tool 5 times by removing it completely from the spindle, reinserting it, and rechecking the tool height versus the baseline. Repeatability was +/- 0.0005″.
Now I have a hard time understanding why people pay so much for the Tormach Tooling System when regular R8 shank tooling seems to repeat so well. If there is more going on here than meets the eye, send me a note. I’d love to learn more.
I got a note from a regular reader who indicates the TTS is all about automatic tool change and being able to change tools a lot faster. Since I have both a powered drawbar I built and a handheld butterfly impact wrench for my second mill, I’m not seeing that particular advantage. It’s a matter of seconds with one of those wrenches, and if you build the powered drawbar, it’s trivial to set it up to work with air solenoids so it can be completely CNC controlled.
Others are concerned about how the holders can sit in the carousel of an automatic tool changer. One can use the indexing ring on the TTS as the place where the ATC carousel grips the tool. That’s a better argument, but you can’t guarantee that with stock tooling. You need a little shoulder on the ring for best results. The problem is the diameter and shape of the tooling below the ring may interfere if things aren’t properly laid out. Tormach sells holders intended for toolchanger applications that have an additional groove. Getting the tools to sit at a defined height in a carousel is one I have some ideas about. More on that later when I finally get to building the carousel!
There is a great thread on CNCZone about creating hypocycloidal speed reducers. The goal of the thread is to create a very low backlash drive for a rotary table 4th axis on CNC machines. I don’t know how successful they are with the backlash, but the designs are fascinating, and several gearboxes have been made:
And here is a video of the gearbox running on its stepper motor:
These are the kinds of projects it would have been impossible for me to imagine someone being able to do in their home workshop. It’s just an amazing bit of work, and one that could only be attempted with CNC.
Someone on the thread suggests these hypocycloid gear systems would make a lovely clock if encased in clear plastic. I agree!
A Vise Tramming Aid for your Milling Machine
I recently came across the idea of a tramming “key” to be installed in the jaws of your milling vise. The idea is due to John Stevenson and looks like this:
Insert the U-shaped key in your vise jaws, tighten the jaws, press the key against the top T-slot edge, and tight down the vise. Nothing could be faster or simpler!
Here are rough dimensions for a key to fit a Kurt D675…
Mikini: Another Little CNC Mill
Neat little mill whose headquarters is right near where I live:
I like the way this enclosure is set up for a small mill. Looks like full width of the table for the door, and that is acrylic. The sides are for the table travel and are metal. There is an access panel on the ends…
Good view of the interior of the enclosure and other details like the gas springs that counterbalance the head or the nice metal way covers…
Sieg’s “Mini-Tormach” CNC Mill: The KX-3
Another very cute little CNC mill:
It’s all nicely integrated. Some more picks from a CNCZone thread:
Power supply and axis drivers on the left, spindle board on the right…
That’s the spindle motor underneath the sheet metal…
A lot of what makes these kind of machines look sexy is just sheet metal. Harbor Freight (and others) sell this one. Wait for one of their 20% off discounts and you’ve got a steal on a turkey little CNC to get started on. If I add up the costs on my IH CNC mill conversion, I probably spent $2k more than you could buy this turnkey cnc mill for. My mill is more capable, but it was a lot more work before I could cut any chips.
Nifty Chip and Splashguard I Just Ordered
This one is made by CNC Automation, and I came across it on eBay. This would sure help control the chips and coolant flying around:
Here it is installed on a knee mill…
The rear is rubber. I assume that so there are no costly collisions with the mill head or rear column…
The splash guard just bolts down to the table’s T-slots. It also bolts to the front slot (where the limit stops go)…
I wound up buying one after thinking about it. My mill is slinging chips all over my work area. On eBay they’re $279. On their web site they’re $500. It’s designed for a 9×42 table, and a 12″ Y-axis travel. My IH mill has a 39.5″ x 9.5″ table and 12.5″ Y travel. I figure that’s close enough.
CNCZone Thread on Engraving Fonts
Pretty good thread over on the ‘Zone about engraving. It starts at bottom of page here. I just thought I’d add that my own CAD program, Rhino3D, has a font function that makes it easy to take any Windows font and convert it to a curve or solid:
I’m going to have to give that a try some time soon. I captured the supplier links for engraving suppliers and added them to my supplier links page as well. Just search that page for “engraving”.
Thoughts on Preloading Ballnuts
You need a pair of ballnuts with preloading between them to really get backlash down to a few tenths. My IH mill CNC kit came with these for the X and Y axes, and used Rockford parts. The trouble for hobby conversions is that they’re pretty expensive. A preloaded ballnut pair is circa $150 for 0.631″ diameter ballscrews. Put these on X and Y and you’re looking at $300. OTOH, single ballnuts are available for $22.85 from the same source. Four singles would cost $80, less than 1/3 the cost. Evidently there is considerable value in making up our own preload arrangement!
The issue when doing so is to suitably place some Belleville washers between the two nuts to force them apart with sufficient preload to do the job, and to prevent the ballnuts from rotating relative to one another as any rotation can reduce the initial preload.
Here is one person’s attempt at this seen on CNCZone:
Those are the square Rockford ballscrews in 0.631″ size. You can see there is a collar threaded onto the lefthand ballnut’s mounting threads. It holds the Bellville’s which push against an inside lip on the left and the body of the ballnut on the right. So far so good. The bracket on top is attached via 2 of the holes that hold the ball bearing return tubes in place on the ball nut. It keeps the ballnuts from rotating relative to one another. Just one problem unless I’m missing something: the bolts are also keeping the ballnuts a fixed distance apart which prevents the preload from working its magic. The nuts have to be able to “float” along the axis of the ballscrew.
Here is an alternative way to machine that bracket so the lefthand ballnut can move:
A slot allows motion. Ideally we’d use a shoulder bolt on that lefthand side so that we can tight down the bolt and there is a nicely machined shoulder that rides in the slot. I’m still not thrilled with the thin plate, but this design would at least allow the nuts to move along the axis relative to one another without rotating as is desired.
One could also envision a design that uses a dowel pin to slide in and out of a hole in a bracket mounted in the same bolt hole, or even a design that is integrated with the ballnut mount. For example, here is a ballnut mount integral sketch:
In this design, an outrigger from the ballnut mount (green) provides a sliding track for the rear ballnut (ballnuts are red). The Bellville preload assembly (gray) is threaded onto the rear ballnut and bears against the front ballnut.
And here is yet another approach originated by Country Bubba and then followed by Pete from TN on CNCZone:
There is a cylindrical housing for the Belleville pack, and a socket head cap screw goes through one of the holes around the rim to lock the ballnut from rotating once the preload is set. Very simple and elegant design.
Hossmachine’s Amazing Sieg X2 Vertical Machining Center
It’s pretty amazing what’s possible in the hobby CNC world. Here is a video from hossmachine:
What’s going on here is amazing. He’s built his own toolchanger, powered drawbar, flood cooling system with enclosure, tooling plate on the table, repeatable Z tool holders (like Tormach’s tooling system), and a whole bunch of other goodies. Amazing to watch it go through its paces. It’s a full on VMC built on a hobby budget from a little Sieg X2 imported mill.
First CNC’d Parts + Watch Out for those Out-Of-Spec Endmills!
I finally got started making parts with the newly CNC’d Industrial Hobbies mill. It was a lot of fun last weekend, and eventually the following parts emerged:
My first CNC parts. The one on the left has an 0.010″ finish pass, and the one on the right is just roughed with a 0.050″ depth of cut. The parts were profiled with a 3/16″ 2 Flute end mill. This photo represents about 3X magnification over actual size. Full details on how I made them are on the Comber Rotary page…
These are bearing blocks for Elmer’s Comber Rotary Steam Engine. They’re for another HMEM Team Build I am participating in. These are trial runs and not finished parts, although the one on the left was intended to be. Unfortunately, when I measured it, there were a number of dimensional errors amounting to several thousandths in a variety of directions. After wracking my brain quite a lot, I finally mic’d the diameter of the 3/16″ end mill. It came out as 0.1837″ which is considerably different than the 0.1875″ that was expected. That would account for a lot of error! Now I need to adjust either the g-code or Mach-3’s tool wear offset to account for that difference and run a new part. I’ll check it again, and if that doesn’t bring tolerances to acceptible levels I’ll keep looking for more things to fix.
Carld’s Really Slick Carriage Stop for the Lathe
Here is a real slick idea for a carriage stop made by Carld over on the HSM board:
It consists of a piece of threaded rod, a micrometer dial, and a pretty typical clamping solution to the way. There is a set screw that locks the stop by bearing on a groove cut in the threaded rod. The edge of the block serves as an elegant but easily read micrometer indicator pointer.
Here are some more pictures:
The groove that rides on the lathe ways was cut by placing the block on V-blocks so it rested at an angle and then using an endmill…
Click here to see another fellow make up a bunch of these for his shop classe’s South Bend lathes.
Handy Power Tapping Tip: Use a Little Impact Wrench
I first started messing with these little butterfly impact wrenches from Harbor Freight when I built a powered drawbar for my mill from one. It worked so well I bought another one of the little wrenches to use for other things. Here is what they look like:
That’s the wrench on the right. The air cylinder on the left was the other component of the powered drawbar I made…
One day I was laboriously tapping a bunch of holes by hand and I spied the wrench hanging there. “Isn’t there some way to use it for tapping?” I wondered. Low and behold, I came across the following little gizmo from Enco not long after:
Tap adapters turn the impact wrench into a handy power tapping device!
I’ve seen others use cordless drills, but what I like about this wrench is the way it fits in your hand, is easily adjusted for torque via the regulator, and can be reversed with the one touch paddle switch. Tapping sure goes fast with one of these, and I’ve yet to break a tap. I keep the torque relatively light and the wrench just stalls out before anything too terrible can happen.
Next thing I’m going to do is build a parallelogram linkage to make a tapping arm similar to what John Stevenson shows over on the HSM board:
He’s using an air drill…
Gas strut is a counterbalance for the weight…
Disassembled view of the torque limited tapping chuck that came with John’s tapping head. The torque is limited because 3 ball bearings in little pockets mate with the tapping head to drive the tap chuck. The balls are held in the pockets by the belville washers. Apply enough torque and the force from the washers is overcome, the balls pop up out of the pockets and nothing more happens. John is concerned the the impact “hammer” action is bad for the taps, but I’ve had no problems. This little impact wrench doesn’t have a lot of guts to screw things up except perhaps on a very small tap. He does suggest it would be possible to disassemble the impact wrench and stop the hammering, and I may look into that at some point.
You Gotta Love Solid Modelling
These are models of a scratch-built CNC lathe that recently changed hands from S_J_H to rubes as portrayed on HSM:
Gorgeous renderings, eh? These were done by Autodesk’s Inventor 2009. I must say, the rendering built into Rhino3D (my CAD program) doesn’t do nearly this well. They have a separate rendering program, but I haven’t wanted to spend the money. I wish they’d incorporate some nicer rendering in the base product. Clearly their competition has.
How Do You Keep the Cylinders In Line Without the Con Rods Interfering?
A fellow was asking recently how to design a model engine so the cylinders could be exactly opposite one another without the con rods interfering. Normally the cylinders on opposing banks of a “V” engine are slightly off so that the con rods can ride side by side on the crank.
One approach is used on this full side radial engine I saw at a local air show:
Note the planetary gear set up front…
Close up of the con rods. Interesting how there is a fork and then one smaller con rod in the middle…
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