Once you've got the mill trammed, your next step is very likely going
to be putting a vise onto the table. Here's how various folks on the web have reported tramming their vises:
Does the vise attach by bolts into the T slots of the table? if so,
then you have a simple way to check square, you need a dial indicator,
an indi-col device, and then put the indicator into the indicol's small
end, and put the large end onto the spindle, and run the table's X axis.
the amount of change or angle on the indicator will tell you which way
the vise need to be adjusted its a long process but you will get it
Mount an indicator in a drill chuck, bearing on the fixed jaw of the
vise. Traverse the table (X axis) back and forth, and adjust the vise
position until you get the same reading at both ends of the fixed jaw.
Given that you have a swivel base, there's a shortcut to get you close:
Take a reading at the center of the jaw, then at one end. Calculate the
difference between the two readings. With the indicator still at the end
position, rotate the vise to remove HALF of the difference. Several cautions:
1) Make sure the indicator arm is actually moving. I've seen people do
this with the arm hard against the stop, and think they have the vise
adjusted perfectly 2) If the jaw is mounted with two screws, take a reading
directly above each mounting screw and use these to determine whether
the vise is square. The pressure of the mounting screws can distort the
jaw. If the jaw was ever mounted with any dirt or contamination underneath,
it can be permanently distorted, even if the obstruction was later removed.
3) Make sure the fixed jaw is straight in the first place. As noted above,
it can be bent by the pressure of the mounting screws. This may be a bigger
challenge than squaring the vise on the mill.
Quick and dirty... clamp a dowel or other piece of bar stock in the
spindle. Tighten one side of the vise pretty well and leave the other
just barely snug. Just make contact with dowel on the face of the fixed
jaw at the tight end of the vise. Move loose end to where it is definitely
a bit out of line. Crank table under spindle with dowel in contact with
the fixed jaw. When you have gone the entire length of the jaw, come back
and make one more pass for insurance. NOW break out your DI and tweak
it if you don't like what you see. I did this today for a quick setup.
When I put the DI in to check, I had less than .0005 in 4" on the vise
jaws. Close enough for what I was doing by far. Same deal with a horizontal,
but grab a fairly large diam slotting cutter very lightly with the vise.
Tighten the bolts. Put a DI on it now. If the vise jaws need to be parallel
to the arbor, you might be able to come up enough to grab the arbor the
same way. If not, do it the hard way.
To get the fixed jaw close, I'll use either a drill bit or a dowel
pin in a drill chuck. Set a gap by eye at one end, duplicate it as best
as possible at the other end. Once you get it where you can barely tell
the difference by eye it's time for the indicator. Saves being way off
and having the test indicator needle spinning wildly and forgetting which
way is which.
Some vises move only a tiny amount from loose to tight - my Kurt changes
less than .010, with the table bolts pulled forward. Others move at least
one time zone. With those, as Bob said, snugging the bolts and making
final adjustments with a hammer is the easiest way. An 8 oz ball-pein
is a good size, small enough that you won't damage the vise. If you vise
is newer, or has newer jaw plates, indicate directly from the fixed jaw.
If the jaws are well used & look like the surface of the moon, a tall
parallel (clamped in the vise) gives the indicator a nice surface to contact.
Last but not least, in Secrets of a Machine Shop, the author mentions
that you can eyeball to within 0.002" by putting a piece of long
stock in the vise such that you can eyeball the visual gap between the
stock and the table's edge. This assumes that edge is actually parallel
to the table's motion--something to be checked on an Asian import!
You could also use a steel rule. One fellow starts out with the rule
in the vise, eyeballing the gap. He claims his accuracy with the rule
is 0.010", which is a good place to start with an indicator.
Do you hate tramming vises? Well, it's not that hard and you should be used to it by now, but there are faster ways.
You can key the vise to the table's T-slot so it drops right into place:
Keying a vise to your table...
Don't want to key the vise? Well, you could make a little gizmo to go in your vise jaws that accomplishes the same thing. Something like this idea due to John
and Drilling On A Hole or Round Feature Accurately
Use a Coaxial Indicator to Center on a Hole or Round
I got a knock-off of the Blake
Coaxial Indicator from Shars and after trying it out decided, "Man,
what a cool gadget!"
Here it is in action as I center
the spindle over a hole so I can use my boring head to make a shoulder
on the hole:
Picture that long
feeler as being sort of like a very exagerated finger from a dial test
indicator. It goes against the inside of the hole, or there are curved
feelers for the outside of a round boss. You turn on the spindle at the
lowest rpm, say 100rpm, and hold the horizontal rod. This keeps the indicator
facing your way while the feeler sweeps around the circumference of the
feature you want to center on. As the feeler sweeps around, the needle
will "kick" because the spindle axis is not centered. Now adjust the X
and Y axis handwheels until the needle kicks as little as possible. That's
all there is to it, you are done very quickly. What a nice gadget!
Adjust the axes
one at a time and don't even think much about what's needed. Simply turn
the wheel and observe whether the needle kicks more or less. Turn it in
the direction that kicks less. When you've minimized the kick on one axis,
do the other. I circle back a second time around and got to almost no
kick at all.
I did not set
up the Indicol and DTI to check the result as I was in a hurry, but visually,
after I used the boring head to make the shoulder, it looked spot on.
It tool longer
to stick the Blake in the R8 collet than it did to adjust the X and Y
axes, or so it seemed. Apparently they can also be used to dial in a 4-jaw
chuck. I'm going to love having this little gadget around I think!
Make sure your mill is trammed in properly before attempting any accuracy
drilling or boring!
Couple of suggestions...
-use vee-jaws for a better grip on the part (4points of contact instead
-use a 120 deg spotting drill rather than the center drill...cups
the drill point better IMHO and just as rigid
-lock table & saddle gibs as suggested...noting any change in the
DRO readings and compensating appropriately.
On the center drill, if you use one, and I understand why, they are
short, rigid, and common in the shop, so only use it to SPOT, then it
is a 118 degree spotter, all is good, don't drill deeper than the drill
point, and surely don't drill deep enough to actually start to get a center.
I elarned how bad this is for the following drill in harder materials,
the tips of the flutes start cutting first and get chipped, it cannot
be good for the drill in softer material either is my thinking.
It comes to mind your mill may have some "lost motion"
somewhere, so with a good indicator you can dial in, and come back to
0 on the DRO from differant directions and see what ends up happening.
Also I have never seen this, BUT your quill travel may not be square to
the spindle bearings, I cannot imagine how that could happen on a good
machine, but you can check for it.
It sounds to me like you are getting a reasonable result for drilled
holes. Use a new centre drill and a new, good quality, drill. Make sure
you ease the centre drill in, using high revs, cutting oil and clear often.
Same with the drill, slow down to correct speed, cutting oil, clear often.
Don't use re-sharpened drills on a job like this, keep yourself a good
set for jobs like this. I disagree with the idea of only dimpling with
a centre drill. Make a decent centre in my experience. Maybe you need
to start thinking about boring your holes if you want exact locations,
but this will slow you down a lot, single point cutting is a another (harder)
skill to learn!
As to making a "good center" with the center drill, trying that in
some 4140 HT or even harder stuff will illustrate the condition that learned
me to NOT do that, actually a 120 degree spotting drill is better anyway
but not as commonly avail within arms reach in the shop. if a hard material
chips off the drill tips when running a 118 drill into a 60 degree center,
I have to think the same process occurs with softer material, but is not
as apparent because it is not as extreme. If you watch, feel, and listen
to a drill you can tell it is unhappy when starting (sounds japanese eh)
but it gets very happy when fully engaged and doing the job it was made
to do, a 120 spotter gets it to the happy place quicker :-) I agree "spark
out" of the drill with the quill against the depth stop (or a short G04
in cnc)helps get a better location, it gives any spring in the machine
and setup a chance to work itself out. I never want to seem to cut down
anothers experience, their method may sure add quality to MY work if I
apply it, and I think the key is finding the WHY in the process that makes
great parts, sometimes it is not truly a result of the intent of the guy
that found it but it cannot be denied that it works. I also wanted to
add that adding a "boring" step to the process with an endmill in a collet
can truly make for better positions, honestly if the endmill is only taking
out a little per side it may be truly as accurate as single point boring,
and a following drill or reamer will follow very close to that established
position. The drill generally "wants" to go straight and starting it off
that way helps it do that...they can and do wander as depth increases,
but if they are started off position they cannot help but walk like mad.
Dealing with Runout, Especially When Reaming
If you have runout, consider the following. If you have an ER collet
you can tap the tool in. Measure, find the high spot and keep taping it
until it gets runs true. Works with collet holders but not usually EM
holders. We do it at work all the time seeing as harldy any of our machines
run true. They all need new spindles as far as runout is concerned. Good
tapers, bad bearings, usually. one of our machines runs dead nuts untill
you clamp a tool in the spindle and put tension on the bearings... Then
it is out .0015 at 6 inches from the face, which with PCD Reamers is not
Here we go again guys. From the men at Spindle Grinding Service.....Check
the taper. Not only for runout, but use some Dykem 107 high spot blue
on the holder and clamp it in to check contact. If the taper is worn it
will cause runout in your holder. That would be my very first check. Something
tells me that is the problem. Could possibly be drawbar pressure, but
the taper would be my first guess.
Precision Reaming Dowel Holes
Whenever we get an oversized dowel pin hole we get out the ball bearings.
Stick one in the offending hole and give it a tap with a hammer. Now the
pin will hold securely, and as long as the hole location was correct before
it should work for you now. I've had to do this more times than I care
to recall. Now this is for in-house tooling. I don't think I could sell
this to anyone if they saw me doing it. With the pin in it though, you
can't even tell. Also, with reamers the top portion of the shank is annealed,
and will "float" into the hole without boring it. If you hold it below
the anneal you will end up with a very inaccurate boring bar.
The ball bearing idea is a good one, but not for pallets that my customer
needs to work with. In house though this is an excellent idea. Any thoughts
on diameter of ball to hole? 2X? 3X? I only ask because too small a ball
would put a lot of force radially outward and too large a ball would put
a lot of force axially downward. I need to think about this some...
We do a lot of dowel pin holes, up to 1/2". We have had good luck
by spot drilling, drilling about .030" undersize, boring with a 2 flute
end mill that is .015" under, & then reaming. The endmill is chamfered
about .030" x 45 deg, & most of the flutes are ground off, leaving about
1/8" of full diameter at the front. We use from .006" to .012" IPR feed.
Using the endmill gives a quick & dirty way to get true position & the
reamer will follow the hole. This process is not as good as boring for
true position but is pretty close & a lot faster. Sometimes to repair
a loose dowel hole, I will tap it with the same size form tap, i.e. 1/4-20
form tap for a 1/4" dowel. The tap will raise ridges to tighten the hole
and with a little loctite, I am done. We also made an alignment block,
just like a tapping block, with about .002" clearance for the dowels.
It makes dowel installation easy.
More Boring Accuracy
the flex in deep holes on a 2 flute cutter by grinding down one
flute. Now the cutter acts like a boring bar.
Interpolate the hole with
the largest endmill that fits (to reduce flex) and leave a small amount
for a finish pass with a reamer.
If you're getting long
stringy chips, you're going too slowly. Turn up the spindle speed.
Prefer feed speed to
spindle speed wherever you can.
I find I'm often going
to slow. Recommended RPM's:
Stainless steel work
hardens, so turn the spindle slower and use a lot of pressure on the
feed. You have to cut through quickly before it can work harden.
Most say the extra cost
of cobalt bits isn't worth it except for very special cases.
Any hole more than 3-3.5x
the diameter deep is a deep hole and needs care to be taken to succeed.
Peck drilling is the norm beyond that depth. The exception is work hardening
materials. Peck drilling can lead to work hardening in a hurry. Do some
special research about how to approach these situations.
(Applies to Lathe and Mill)
Tip: Brushing on
a coolant will increase the range of optimal speed. In other words, it
lowers the speed where things work best as well as raising it, creating
a broader "sweet spot" of speeds that is easier to hit. If you
are having a hard time getting things cutting nicely, why not try a little
coolant? If you are using carbide, be careful not to drench the coolant
in suddenly, especially if things are running pretty hot. Sudden cooling
can crack the carbide. Apply the coolant steadily and from the beginning
of taking the cut.
Tip: Different materials
and operations respond to different coolants. I keep a set of condiment
squeeze bottles (cheap at the dime store) ready to hand with the following
- Tap Magic
- Heavy Sulfurized Cutting
Some folks also do well
by spraying on WD-40, and there's always a couple cans of that floating
Tip: Coolant can
improve surface finish and tool life. Interestingly, it can also reduce
tool life after you exceed certain SFM's--see Dry Machining below. One
of its major roles in both improving surface finish and improving tool
life is clearing away the chips to minimize chip recutting. BTW, this
is one of the great advantages of climb milling as well. Getting the chips
out of the way can be done with just a steady stream of air directed at
the work, so by all means, try that if you have compressed air and don't
want to mess with coolant.
Tip: Dry Machining.
Most tooling reps advocate shutting off the coolant over 400 sfm and going
with dry machining. You should still use a blast of air to clear the chips,
however. The consensus over on Practical
Machinist is this really works well to increase tool life. Some few
think you still get some surface finish advantages to use some coolant
during the finish pass.
When roughing, an air-water mist is fine. For finishing, use a cutting
Cutting oil will reduce
chatter. Chatter is just a harmonic resonance, so anything you do to change
the "tuning" of the instrument can reduce the chatter. Speed
up or slow down the spindle if you have variable speed and you can often
get rid of it too.
Rumor has it to use "A-9" aluminum cutting fluid for the finest aluminum
finishes. Green can, green fluid, much better than parifin, kerosene,
lard, or WD-40.
Widgitmaster's coolant of choice:
Actually I bought the Synthetic Coolant, it mixes with tap water at 6oz
/ gallon, it has rust inhibitors in it! This coolant it water clear at
first, and gets a little cloudy as the way lube gets mixed in! I have
not had any rust, and this coolant dries leaving a sticky film of oil!
It works really good on aluminum, stainless, cast iron, steel and plexiglas!
Enco #325-6565, $36.16 per gallon of MISTIC-MIST concentrate, makes 30
The fog buster is a coolant option many recommend, particularly those
that don't want to deal with the mess of flood cooling and are afraid
of the health issues associated with coolant mists (bad for the lungs).
A fog buster delivers a stream of coolant embedded in an air stream without
converting the coolant to an aerosol mist. The end result is the coolant
winds up on the workpiece and not in the air:
The Fog Buster works this way with a single needle valve serving as a
mixture control. Since the Coolant and air are pressurized equally, and
the air is the mainline, the single needle valve acts as a mixture control
to limit the amount of coolant added to a fixed amount of air. The net
effect is that with a single needle valve you can dial all the way from
a near flood coolant to pure air. If you search the message archives,
Mike Hanz posted some great pictures and a parts list for a homemade Fog
Buster back in 2003. He used a precision "panel" needle valve from McMaster,
part number 48965K24. This needle valve counter-sinks into the brass block,
so you get a neat, compact package without the valves hanging off the
ends. Mike also turned me on to the water filter canister, part number
4422K3, for the coolant reservoir. This is the same tank the commercial
Fog Buster unit uses.
I think that were I seeking a coolant option somewhere between a chip
brush and flood cooling, and more than just an air stream, the fog buster
would be ideal. I'm not sure it is worth the trouble to make versus buy,
but it isn't a very hard project either.
Accurate Z-Axis Adjustment on the Mill (aka I love
it when a gadget actually works!)
In working on the Turner's
Cube, being able to determine Z-axis precisely is imperative. In addition,
I am still having a hard time achieving the level of accuracy I routinely
get on my lathe over on my mill. On the lathe, getting it accurate to
a thousandth is never a problem, and even if I am not paying much attenting,
things come within 3 or 4 thousandths. I haven't spent much time fiddling
with tenths yet, but someday I will. On the mill, I seem to be doing good
if I hit the high single digit thousandths, say accurate to 7 or 8 thousandths.
I know its my technique, and its just not good enough.
I mention somewhere below that one has to allocate time
to experimentation, so tonight I resolved to experiment with z-axis accuracy,
and along the way, dug out a purchase I had almost forgotten to test for
the purpose. In the end, I tried four different methods. In each case
I used my granite surface plate and digital height gage to determine how
closely I had come.
Using the granite surface plate
and height gage to determine z-axis positioning accuracy...
To use the height gage, I zero it on the 1-2-3 block and
then add 1" to the reading off the top of my aluminum cube. On the
mill, I used each of 4 methods to find the top of the block, zeroed my
quill DRO, dialed in a desired depth of cut
with the fine quill adjustment, made the cut under power
feed, and then checked how close I came to the expected result. Incidentally,
the process of finding the top of the workpiece (or side on a lathe) is
called a "touch off."
Here are the results of each z-axis setting method:
Touch off by feel: For my 1st Method,
with the spindle stopped, clunk down the cutter onto the top of the workpiece.
Zero the DRO and go from there. This produced a result with an error of
0.012". Not very good! The error was relatively repeatable, so one
could add the fudge factor. In the end of the day, the cut was 0.012"
deeper than desired.
Touch off by sound: For my 2nd try, I
was gently lower the spindle under power and listen for when the cutter
started to cut. This method proved slightly more accuate, and resulted
in 0.0085" too deep a cut. Still not very good.
Touch off with paper: The traditional
old school method involves holding a piece of cigarette paper (rumored
to be exactly 0.001" thick) on the workpiece and gradually lowering
the cutter until it starts to catch the paper. Add another 0.001"
and you are at zero! Not having any cigarette papers, I used standard
laser printer paper. I cut a 1/2" wide strip so I could hold onto
one end from a safe distance, and waited for the cutter to grab. In my
case, I got a grab at 0.010", not 0.001", but at least it was
a nice round number and pretty repeatable.
Z-axis Presetter: At this point, I thought
I was done and would be using the good old paper trick. But I had a vague
recollection that finally came back to me. Did you ever by a gadget that
looked like a good idea, but before it ever arrived you started doubting
it would work well, stuck it up on a shelf, and never actually tried it?
I do that way too often. In this case, thing I remembered was a Z-axis
Presetter I bought off eBay around 8 months ago. Search for "Z Axis
Presetter" on eBay, and you'll find the ubiquitous 800watt listed
Chinese machine tool gadget. They look like this:
A Z-axis Presetter from eBay seller
I have a dim recollection of some CNC guys
recommending one of these to use with CNC machines. How does it work?
Simple. There is a little knurled knob visible on the bottom left. It
has a "test" and a "use" position. Set it to "test"
and an internal standard swings into place so that if you press the anvil
on top with your finger until you hit the stop, you'll have exactly 2"
from top of anvil to bottom of gadget. You rotate the dial to zero in
that position. Now reset the knob to "use", place it atop the
workpiece, bring the cutter down until the needle registers, zero the
needle, zero your DRO, and you should be exactly 2" above whatever
the presetter is sitting on.
So, not expecting much, I plunked the sucker
down atop my aluminum cube in my Kurt vise on the mill, cranked the head
until the cutter almost touched. Locked the head and cranked the quill
with the fine adjust until the needle zeroed, zeroed my DRO, removed the
presetter, cranked down another 2" with the fine adjust, zeroed the
DRO again, added 0.010" for a modest cut, ran the cube through under
power feed, and hauled the block over to the surface plate to see what
I had done.
The desired result was 2.396". I brought
the height gage down to take a reading which was, drumroll please, 2.396"!!!!
Holy uncanny accuracy, Batman! The silly
presetter actually worked, and it worked well, and even though the quill
travelled 2", and I expected the worst, it came out deadly accurate!
Hooray for the gadget that actually worked.
I guess I'll be using the silly thing more often. At $39, it was worth
Playing With Blocks (2-4-6 Blocks, That Is)
I always look carefully when an experienced machinist
is showing how he has done something. Here is the Fidgiting Widgitmaster
showing how he squared a 6" x 6" plate in his vise using 2-4-6
blocks to lend support (they stick up out of the vise pretty far otherwise):
Squaring a plate in the vise with
the aid of some 2-4-6 blocks for support...
Made me want to go buy a set of 2-4-6 blocks, although
they sure aren't cheap!
A fly cutter will often produce
the best surface finish because they allow you to finish a very wide area
in one pass with no overlap marks. They make a distinctive sound as their single cutting edge
makes its cut on the workpiece. It's a noise that drives some machinist's
crazy and can best be characterized as a loud thumping (often called "hammering") that sounds like
its about to tear itself apart. You can easily convert a facemill to a flycutter by removing all but one insert, and it is interesting to experiment with the results. Reducing the number of inserts will necessitate a reduction in feedrate, but it may be worth it in terms of improved surface finish.
Some people swear that the best finish for aluminum is a flycutter large enough to cut your material in a single pass equipped with a PCD insert of the largest possible radius.
Like most mill cutters,
your fly cutter will perform better with positive rake on the cutting
tool. I haven't yet seen any positive rake brazed carbide tools (which seem like the most common thing people stick in their flycutters), so I
suppose you would either need an insert like a CCMT or you'd need to grind
your own tool from HSS with some positive rake.
Someday I want
to build an R8 fly cutter that has a built in CCMT insert. I'll use a
design similar to my dovetail cutter,
and I don't think it would be a hard tool to make.
Here is a sample
of the surface finish possible with a fly cutter and off-the-shelf brazed carbide lathe tool:
Not bad, not great finish...
This was one of
my first cuts with the tool, I was squaring a block for my vise stop project.
I didn't run the spindle nearly as fast as I should have for a great finish,
but it still came out pretty decently. The moral of the story is that
fly cutters are cheap and easy to use.
Fly cutters are
very sensitive to tram. If you think about it, the cutter is apt to cut
a concave instead of flat cut if your mill's head is not trammed properly.
Watch your workpiece carefully as the leading edge moves through the center
of the fly cutter. All the cutting should have been done as it was travelling
the first half of the way if you head is in tram (think about it carefull,
that's one geometry for one direction, so you actually have to see this
behavior cutting in both directions to be sure). If it cuts more on the
second half, you can be sure the tram is such that the head has that half
tilted downward slightly. You can see the tramming effects in this photowhich has had the cuts accentuated via some Photoshop tricks:
The mill head
is close to being in tram, but you can see that one set of marks is a
little heavier than the others. If you're really out of tram, you can
only see one set of marks. Also, the larger the fly cutter diameter, the
more the tram effect is exaggerated.
If you are going
to grind your flycutting tool, here are some useful pointers I have gleaned from
my Internet travels:
Fly Tool Cutter Geometry
Here are photos of a flycutter cutting tool that was given to me by Widgitmaster from CNCZone. This is the geometry he uses when flycutting aluminum for his mini-routers, and the surface finish is superb:
It sits in the flycutter with a slight down angle like this. Note the large smooth radius of the cutting edge, and the considerable positive rake...
A little more oblique view of the cutting edge. You can see how it is relieved from contact from the workpiece except along the cutting radius...
From behind the cutting edge. I've got a little divot in it, unfortunately. The edge is somewhat delicate and should only be used for aluminum...
The underside of the tool...
The surface finish Widgitmaster gets on his aluminum work is nothing short of spectacular with one of these!
Miscellaneous Tips and Techniques
A note about gibbs. On column mills, the gibbs affect the tram of
the head. If you like to tighten or lock them every time you perform an
operation, you will limit the accuracy of your head tram. Better to adjust
them fairly tight perhaps 4 times a year, tram after the adjustment, and
then leave the gibbs alone if best accuracy is desired.
Tramming your mill to a "thou or two" may not be good enough.
If you move your table to a different spot to drill than where you indicated
your part at you get projected error. also, try a test indicator in an
indicol rather than your co-ax it will tell you if your co-ax is cheesy
or not. I recommend Interapid.
Use a singlepoint test indicator...the coax relies on a mechanism
and precision alignments and fits therein. I am a fan of Interapid's offerings
in that category.
Do yourself a favor, spoil yourself and buy an interrapid incicator,
I bought a .0005 and aquired a .0001 over 20 years ago, the .005 has been
repaired once, otherwise they have served me faithfully ever since, their
only downside most of us machinests never see is they are effected by
strong magnets, so guys that only grind don't use them...turning on a
6" permag chuck will damp .0003 tir out of an interrapid...didnt
belive it until I was shown it by a man with far more experience ID grinding
Other than that hands down they are the nicest deal going, a guy turned
me onto them back in 1984, so I guess it has been 22 years...I was 19
then hehe, 41 now, still on that same indicator.
Never move the knee after picking up location. Learn to tram head
dead nuts on a 6" circle. When the head is not trammed dead nuts and you
move the knee, the location changes. If you are out .004 on a 6" circle,
and you move the knee 3" after removing your co-ax, you are now off .001
on location. In addition to the Interapid, get an Indicol that will attach
to the spindle with a tool in place. This will allow you to use your indicator
at any time. The easier it is to use, the more often you will use it.
Also, get a couple of small mirrors to read the dial when its facing the
column. Sticking your neck around back gets old very fast.
I did not think about the knee changing the position of the tram,
however, I was aware that the quill would throw you off, for example,
if you tram the head with the quill retracted, and make your cuts with
the quill extended several inches. It just magnifies your tram error,
The reverse also works, if you tram your mill with the quill fully
extended, then the accuracy is higher when retracted.
Tram your head over the largest circle you can swing (ie the width
of the table). Use a dial or finger indicator and read directly on the
table surface. No blocks, rings or anything else required, all will introduce
error. Personally I tram the head without locking the knee, because I
almost never use the knee lock at any time for the work I do. Centre you
workpiece with a finger type indicator of some sort, the result will be
right, whereas it sounds like the Coaxial type are not always trustworthy.
You can even use a plunger-type indicator if that is all you have, and
if you have enough room. The magnetic base will stick to your drill chuck
and away you go. Sounds clumsy (it is) but use what you have. I don't
take much notice of the suggestions about not moving the knee, sometimes
you have to. Try not to, ie plan ahead.
I once had a guy working for me that had a Blake Co-ax. He scrapped
quite a few parts before I made him stop using it. Unless the quill is
in perfect tram, you are changing the center location, if you move the
knee up or down, after you indicate the center of the workpiece. Error
can be even more, if there is any wear or play in the knee gibs.
One more thing to try: put a cylindrical square on the table, and
use an indicator to check whether the z axis is parallel to the square's
axis. It could easily be that your z axis ways have excessive wear and
its time to rebuild.
It's VERY IMPORTANT to always lock the vertical travel of the knee
before you do anything, whether it's taking a measurement or making a
cut. With the knee loose, it will pull away from the column, but the magnitude
and direction of the movement are unpredictable. Whenever you unlock the
knee, its final position depends on the amount of weight on the table
and the location of the center of gravity. But the center of gravity changes
every time you move the table on either axis. You first position the Z
axis as required, then lock the vertical travel, then do whatever else
you need to do.
On assuming your tram is goodt. We re-indicate the tram every morning,
before every fresh setup, after heavy milling, after a suspicious measurement,
and of course, after a crash(tho'that's never happened to me ). In mold
work it is imperative as you usually doing onesy work and weld is so detrimental
to the life of tool. After a week of indicating the whole shop in it is
quite second nature and takes little time.
As for the rig to indicate with we always called this a "tram
bar". I find indicol's and those silly Co-ax indicators a waste of
money. I made this bar by tracing off my mentor, he traced his off of
his mentor and who knows where the pattern started. In this part of the
country this type tram bar is common in many mold shops and other shops.
It is a simple project and was the first tool I made when I took up mold
It is simply CRS c&h with an ejector pin (drill rod will work)
for a post, all thread for the screw, the universal sleeve is from Starrett,
and then a ball swivel from Starrett or B&S. I welded an extension
to the swivel. This rig will tram all the diameters and squares you will
see. If needed a second snug and rod can be added to extend range. This
will clamp down and bite hard and not wiggle or droop (a problem with
the half baked Indicol with the nylon friction washers. Do yourself a
favor and whittle out one of these and you'll never have any issue with
mystery location and flyer holes.
well i have to make a coment or two here. first i stone the table
to remove any burrs then i use a 1" gauge block under the indicator so
i dont worry about the indicator jarring or moving due to jumping over
the T-slots. second in reference to the Blake coax use. these indicators
are so quick to use for an initial location it amazes me anyone would
not want to use one. but having said that i always go back and tweek the
last few thou with at least a .0005" indicator but usually with a .0001"
indicator, after all if your within .005" or less it just takes a few
seconds to be dead nuts.