Lathe CNC Conversion History
I love my Lathemaster 9x30
lathe, but it lacks several useful things in the gearing department. Changing
speeds required changing belt positions until I finished my variable
speed DC motor mod. There is no tumbler
reverse, and fabricating one is difficult given the way the gear train
works. Meanwhile, if I want to reverse the leadscrew, I have to manually
insert a reversing gear and move one of the other gears to mesh with it--not
a simple operation. Cutting threads is even harder. There is no quickchange
gearbox, just a stack of gears that need to be bolted to the banjo in
various arcane configurations. I'm a computer
guy, and it seems to me this can all be fixed with some appropriate
computer technology--an e-leadscrew. At the same time there are certain
operations that are just plain laborious (when you have to turn off a
LOT of stock to reach a desired diameter), and certain others that are
difficult (cutting a precise taper, for example) or cutting threads.
CNC can fix the labor and
difficulty issues, but many worry it comes at the expense of spontaneity. You have
to interact with g-codes, CAD drawings, and all that. I just want to make
parts, and I will often start with a back of napkin drawing at best. This
lack of precision and specificity is anathema to the CNC world. It is
no surprise that a lot of sophisticated CNC operations keep some manual
machines in the toolroom for one-off jobs.
But there are answers to the lack of spontaneity problem. There are commercial lathes
available that try to fit this bill. They give the operator manual controls
that include even handwheels. It's just that the handwheels are now electronic
encoders rather than actually driving leadscrews:
CNC with Handwheels and Joystick...
The CNC people call the
handwheels "manual pulse generators" or MPG's. I'll
be looking into the whole idea of MPG's as well as seeing what the current
crop of CNC software offers to the manual machinist who wants to make
one-offs. The Mach software has a great set of wizards for
this purpose. The software is free to download just for looking at, and
most will find the Wizards are straightforward to use.
I will also point out that good CAD/CAM software is amazingly fast to go from a drawing to g-codes. I find I like having a drawing available for what I'm doing, and once I having a drawing, that's most of the way to being able to lay hands on the g-codes. Maybe this CNC stuff can be pretty spontaneous after all!
Brief History of My CNC Journey
The CNC angle is complex
and comes with a steep learning curve. Because of that I started with much less ambitious plans than to
create a CNC lathe. At first, I only wanted a literal replacement for
the gearbox I was missing, so I started circulating
the idea for an electronic leadscrew to see if anyone else was thinking
like me. There was considerable response to my various posts on different
Yahoo Groups boards. The CNC crowd, of course, didn't see the point. Their
view was that it would involve most of the work needed for "real
CNC", so why not finish the job? In fact, these sorts of discussions
became quite acrimonious, to the point where some felt it was time to
branch off the discussion from the CNC boards and have a place just for
the discussion of the "pure" E-Leadscrew" approach. This strong cadre started
the Yahoo E-Leadscrew
Group to discuss ideas and maybe even create a prototype.
Picture losing the gear
train that drives the leadscrew and replacing it with a stepper motor
directly driving the leadscrew. Imagine a little box similar in size to
the Shumatech DRO. Perhaps there's even a way to connect that stepper
to the DRO and with the right software for its microcontroller, to do
just what I need. Now picture the following controls on the box:
Forward/Reverse/Neutral: Determines what direction to drive the stepper
or shuts it off altogether. A software tumbler reverse!
A knob rheostat that allows you to continuously vary the leadscrew speed
when using it as a power feed on turning and boring. Nifty!
A menu of all standard thread sizes both English and Metric. Select one
and you leadscrew magically operates at the correct speed to produce that
thread. You still have to use the thread counter to synchronize, as well
as locking or unlocking the half nut, but this is easy stuff with a little
You would now have total
control of your lathe with the relatively easy task of mounting a surplus
stepper motor and driving it from the magic e-leadscrew box. That's a
lot of my dream come true!
I will hasten to point out
that I am not the first to suggest these ideas. These discussions break
out periodically on the boards. I do believe this is the first time it
has resulted in people working together on the project, which is nice.
The earliest effort in this area was built by a German
engineer who used phase locked loop technology to create an e-leadscrew. I think the whole
thing can be done even more simply with a PIC-style microcontroller such
as what the Shumatech DRO uses,
and this is the approach with the largest following on the E-Leadscrew
group. Another fellow has built an electronic gear train for a gear
hobbing application, which just goes to show this idea may have a
lot of uses for machine tools.
The Yahoo E-Leadscrew Group
has made tremendous progress and may wind up realizing an actual device.
There are at least two competing approaches, and one fellow has built
a very complete prototype and demonstrated that it works on his Gingery
Since having cross pollinated
the idea on these various boards, I've been pursuing the dream myself
in several ways. First, I designed a mock
panel for an e-leadscrew appliance capable of controlling 2 axes and
providing considerably more functionality than the group is currently
talking about. This would result in a "conversational CNC" appliance:
intentionally mimics the Shumatech DRO and is intended to be used alongside
one. It would be an ambitious, but not impossible project to create this
device. I think it is probably very similar to the effort needed to create
the Shumatech itself, and I would think it would have similar complexity
and cost. By all means click on
the links to get a feel for how far this idea could be taken. I don't
know if anyone will take it that far or not, but it is interesting to
Second, I purchased
a Frog CNC controller. The Frog is a single axis CNC controller built
around a microcontroller that is basically an e-leadscrew. It was intended
to control threading and has some limited abilities to do other things. The bad news is
that the guy has quit making them, and is selling of his last stock of
8 units. I jumped at the chance because it wasn't that much money on the
grand scheme of things and I figure I can always resell it or perhaps
use it to control a rotary table.
The frog is
cute as a bug:
Frog CNC Controller
We will see
how well I wind up liking it. There is a Yahoo group aimed at Frog
users if you want to know more. I want to play around with the Frog
and use it as a test bed, but it is unlikely to be my final stopping point
given that it is now an orphaned product. Of course if the E-Leadscrew
gang never finishes a useful gadget, I may have to be satisfied with the
Third, I have
been educating myself about CNC. The motion
control infrastructure needed to drive a lathe axis with a stepper
motor is the same in all cases, so this was the first area I looked into. I got a lucky
break on eBay (again!) and was able to acquire 5 excellent Pacific Scientific
210 oz in stepper motors for only $34:
I think they'll
be perfect for my purposes. You can read more about this infrastructure
work by clicking my links for that as well. I took a brief detour
toying with a design for a simple
manual pulse generator to drive these steppers so that I can use them
simple for power feed purposes. I have laid out the board so that the
stepper infrastructure may be controlled either by the manual board or
a CNC breakout board, which offers another approach to conversational
CNC. One could select either the tactile manual controls or the CNC PC.
In the end of the day I might even rig up a stepper powered manual XY
table for my drill press, but that's a whole other project.
trying to learn everything I can about mainstream CNC, with particular
attention paid to the conversational capabilities. Towards that end I'm
digging through the Internet to learn all about MPG's and looking over
some of the professional (and amateur-built)
CNC control panels that are designed to make this kind of work easier.
I'm studying the manual options for programs like Mach, whose Wizard capabilities
are pretty nifty.
Collecting Parts for the Project!
I'm not sure what I'll finally
end up with. Perhaps a hybrid of all these components.
After this protracted wandering
in the dessert, I finally arrived at a plan, and
a Blog. I would build a CNC lathe around conventional CNC conversion
that I mean I would be using stepper motors
on both axes, Mach 3 Turn software with attendant wizards, and an elaborate
control panel designed to maximize the potential for manual operations
with as little pain as possible. If all goes according to this plan, I
will be able to both run traditional CNC operations, as well as do quick
back of the envelope operations. If nothing else, I'm about ot learn what
the limitations of amateur desktop CNC really are.
Plan, Part 2
Assuming I embrace CNC wholeheartedly,
it would make sense to improve the backlash situation on the lathe with
ballscrews. It is also tempting to try to build my own CNC machine tool
Since I began this journey I have acquired a CNC Mini-Router as well as a conversion kit for an Industrial Hobbies mill. After playing with the mini-router I covet a much larger router, and probably a plasma table too. There seems to be no end of CNC possibilities to play with, but it all started here with the lathe!
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