Building Inexpensive CNC Machines

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Building Inexpensive CNC Machines http://www.fullnet.com/u/tomg/gooteecn.htm
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Used Electronic Test Equipment and Manuals, and New Electronic 
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Curve Tracer Kit page
Gootee Homepage Index
Building Inexpensive CNC 
Machines
for Computer-Controlled Drilling and 
Milling
(This page is under "ongoing construction"...)
(C) Copyright 2002 by Thomas P. Gootee
Introduction
When I started thinking about CNC machines, I just wanted a 
computer-controlled machine that would be able to automatically drill all
of the holes in the printed circuit boards that I made, for my Curve 
Tracer kits (see the link, above). But, the "good" commercially-available 
machines were priced higher than the amount that I could justify 
spending. So, I started thinking about what it would take to build one, 
Building Inexpensive CNC Machines http://www.fullnet.com/u/tomg/gooteecn.htm
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myself. And, I didn't want to build one that would cost almost as much 
as a commercial machine: Otherwise it might have been smarter to just 
BUY one, to begin with! So, I decided to add "low cost" as one of the 
design goals. I also expected to end up with one or more additional 
products to sell, as a result of this project, to (help) justify the time that I 
spent on it.
This page was started on 6/6/02. It should be updated, occasionally, as I 
make progress on the machines I'm building.
Machine Number 1:
Starting a project like this one, while having so little knowledge of what 
is needed to complete it, makes progress very slow, at first. I did a lot of 
searching and reading of the Usenet newsgroups, and many websites, 
through http://groups.google.com. (I do have an electrical engineering 
degree, but had never worked with or studied stepper motors, and knew 
almost nothing at all about milling/drilling machines, nor CNC
machines.)
I learned about stepper motors, and their driver circuits, and the software
used to run and control them. And I saw some of the ways that others
had designed and built their own CNC machines. I also began to 
understand some of the limitations imposed by different types of 
machine designs. I started to get my design goals better-defined, and also
saw where the machine I wanted to build would fit into the continuum of
sizes and types of CNC drill/mill machines, which, by the way, hehe, is 
very near "the bottom": All I needed was a small machine, able to drill 
boards of up to 6"x4" in size, with a worst-case hole-placement accuracy
of about 0.01-inch or so, which would be about 1/3 to 1/4 of a hole's 
diameter (using 0.035" or 0.04" holes). And I didn't need to do a very 
high volume of drilling. I figured I'd be happy if it could drill at least 
2,000 holes per day (although, hopefully, not taking all day to do that!).
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I started to feel like I could probably design and build a machine. But, 
having both my "low cost" design-constraint, and the fear of "messing 
up" on something I'd never done before, I wanted to START with a 
design that would be VERY quick and easy to build, and EXTREMELY 
inexpensive, that could serve as a "testbed" for learning more about 
stepper motors, their driver circuits, and the software used to control the 
machines driven by them. After that, I hoped I would be 
much-better-positioned to build something that was closer to being a 
"real" CNC mill/drill machine.
I had considered several possible designs, while doing the initial 
research:
I considered trying to use an old flatbed X-Y plotter, either to move a 
small drill-head that was at the end of a Dremel-Tool-type flex-shaft 
drive cable, or to carry the circuit board while the drill was mounted 
above, on a separate third axis. Old plotters are quite inexpensive (under 
$50, on www.ebay.com). And I actually already owned some.
I also thought about just building the x, y, and z axes from scratch, using 
threaded rods (leadscrews) connected to stepper motors to move them. 
And I am considering using a purchased "compound slide" milling table 
as the x-y positioner portion of a machine, which would be modified by 
replacing the leadscrews' manual cranks/handles with stepper motors. 
One possibly-big advantage of that approach, which would also be 
gained if building the x-y table "from scratch", using leadscrews, is that 
the leadscrews provide a larger gear ratio, which in turn gives better 
linear resolution, per step. Even the small, cheap milling tables usually 
move each slide-table by 0.1-inch per full turn of the leadscrew crank, 
which would give a movement of 0.0005 inch for each full-step of a 200 
steps/rev motor, as opposed to something like 0.008 inch per step for the 
typical dot-matrix printer's carriage assembly. I am now planning to use 
one of these commercially-available x-y milling tables when I build my 
second machine. I have purchased one, the cheapest ($99) model at 
www.use-enco.com. But, I bought the same make and model, brand new,
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on eBay.com, for only $69 plus shipping (the seller happened to be fairly
near my area, though, so shipping was only about $15, for the 36-pound 
table).
And, I also thought about using two old dot-matrix printers' mechanisms 
to make the x-y positioning system. I didn't THINK that one printer's 
mechanism could be mounted directly onto another one's 
printhead-carriage assembly, because I assumed that the "bottom" printer
wouldn't have enough power to still be able to move correctly, with the 
weight of the other one on it. So, originally, I considered having one 
printer carry the printed circuit board (PCB), with the other printer 
suspended above and perpendicular to it, to move the drill, giving the 
second axis of positioning. However, I still would have needed to find a 
way to move the drill up and down (I was hoping I could figure out how 
to make the printer's paper-feed assembly, and/or motor, help perform 
that task.).
Recently, I happened to find a used-computer store where they had 
dozens or hundreds of old printers that they'd taken as parts of 
computer-system trade-ins, for newer systems that they sold. So, I 
bought some of the printers, for only $5 each! I figured (hoped) that they
would probably be worth more than that, just for their stepper motors 
(and power supplies, et al).
I found out that the IBM Proprinter models have pretty HEFTY 
print-head-carriage stepper motors in them, at least compared to the 
Epson FX-850 and FX-1050 models. The IBMs' motors are 2.25" 
diameter, and about 2" long. (They are Sanyo Denki "Step-Syn" models, 
4.1V, 1.1A, 200 full-steps per revolution, unipolar (i.e. 6 wires).) The 
IBM Proprinters also utilize a screw-type drive system for the printhead, 
as opposed to the cog-belt drive system that most of the other older 
printers use.
I also bought a couple of the biggest, heaviest, oldest "daisy-wheel" type 
printers that I could find, there. One of them, a CPT Corporation model 
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A071, also had the big motors, with sizes just like those in the IBM 
Proprinters: 2.25" diameter x 2" long (But it had TWO of them, instead 
of just one: Minebea Co. Ltd. "Astrosyn" "Mini-Angle Stepper" models, 
6V, 0.85A, 200 full-steps per revolution, unipolar. (The IBMs each had 
only ONE of the bigger-size motors in them, with a second one that was 
much smaller, and coarser-stepped, for the paper-feed roller's drive.)). 
The CPT A071 daisy-wheel printer also had very heavy, solid 
construction, with printhead-carriage slides thatwere a full 5" apart (at 
least twice as far apart as those in any of the dot-matrix printers), and a 
very nice, heavy solid-metal printhead-frame/holder, between the slides, 
which even had roller bearings above and below the slide bar on the 
"little" side (the side that was farthest from the paper path) (See photos:).
Printhead Frame/Holder, CPT A071 Daisywheel Printer:
Roller Bearings on Slide, CPT A071 Daisywheel Printer:
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I stripped a couple of the Epson FX printers, and a couple of the IBM 
Proprinters, one small (8.5" wide) one and one large (15") one of each 
type, down to where I had only the carriage-slide assembly, with the 
printhead-holder/frame, the stepper motor and drive assembly, and part 
of the frame that held it all together. I also did the same with the CPT 
daisywheel printer (see photo:).
Printhead-Carriage Assembly of CPT A071 Daisywheel Printer:
After taking apart the printers and actually SEEING what their carriage 
mechanisms looked like, I began to think that the big CPT A071 
daisywheel printer "should" be able to have one of the small Epson or 
Building Inexpensive CNC Machines http://www.fullnet.com/u/tomg/gooteecn.htm
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IBM model's carriage assemblies mounted right onto its' printhead 
frame. So I thought I would go ahead and try it, since it would be 
*extremely* quick and easy (and inexpensive), at that point. And, IF that
worked well-enough, only THEN I would try to make a z-axis (vertical 
axis) to work with it, to move a drill (and possibly other tools) up and 
down.
To find out if that would work, though, I'd need to be able to actually 
RUN the motor, and move the printhead assembly, to see if it had 
enough power to move the extra weight reliably. So, I got three of 
Allegro Microsystems' UCN5804B stepper-driver ICs (integrated 
circuits; "chips") (I got three free samples mailed to me within a week, 
from http://www.allegromicro.com .) and breadboarded a 3-axis stepper 
motor driver circuit, which took as inputs "step" and "direction" signals, 
so it would be able to be compatible with some of the free CNC 
software, such as Dancad3D, that sends those signals to a PC's parallel 
port. The Allegro 5804B IC, in addition to the "standard" full stepping 
mode that powers two of the four motor inputs at a time, also supports 
half-stepping mode, and single-phase-at-a-time full-step mode. (By 
creating circuitry that could provide different amplitudes to each motor 
input, then, by using certain patterns of the inputs' timing and 
amplitudes, the stepper motors could be made to do "microstepping", 
allowing the use of much smaller step sizes than the motor "normally" 
supports, such as 1/4-steps, 1/8, 1/16, 1/32 steps, etc.; almost any 
fractional step-size, I think; not just powers of 1/2.)
To quickly test the motors (and my driver circuit prototype), I used an 
old Hewlett Packard DC lab/bench power supply that I had lying around 
(old PC computers' power supplies would work well, too), and an old 
Systron Donner "Datapulse 101" pulse generator (like a square-wave 
generator, but with variable width and spacing for the generated 
pulse/square waves, among other things). A simple 555 IC circuit from 
the web would work fine for this, too, and cost almost nothing, with 
parts available at, for example, Radio Shack stores. I used these 
instruments just because they were handy, because I happen to make a 
Building Inexpensive CNC Machines http://www.fullnet.com/u/tomg/gooteecn.htm
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living selling surplus electronic test equipment, such as oscilloscopes, 
signal generators, spectrum analyzers, power supplies, and many other 
interesting kinds of equipment (Click the link at the top or bottom of this
page, to see all of the cool equipment that I have around here!).
I soon had the motors going, and played around with the printers' 
mechanisms. It was quite interesting to vary the frequency and the width 
of the "step"-input pulses. At times, the motors seemed more like 
musical instruments, with resonances only at certain frequencies. I was 
also able to note large differences in a motor's torque, speed, 
"smoothness", and sound/noise level, depending on the pulses' frequency
and widths.
I built a small "mount" assembly, on the CPT daisywheel printer's 
printhead assembly, to make a level base on which to try mounting the 
Epson FX-850 printer's entire carriage assembly, using small aluminum 
channel and angle stock and 4-40-size brass machine screws and nuts 
that I purchased at a local hardware store (see photos:).
Mounting Bases Constructed on Printhead Frame/Holder:
Mounting Bases Constructed on Printhead Frame/Holder:
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I put the smaller printer's assembly onto the mount, on the larger printer's 
printhead-holder/frame (see photo), and powered up the larger printer's 
stepper motor. As I had hoped, the motor had NO TROUBLE at all, 
moving the WHOLE THING, reliably (see photo:).
Epson FX-850 Carriage Assembly, Mounted on CPT A071 
Printhead Frame and Carriage:
Epson FX-850 Carriage Assembly, Mounted on CPT A071 
Printhead Frame and Carriage:
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Epson FX-850 Carriage Assembly, Mounted on CPT A071 
Printhead Frame and Carriage:
So, right now (6/6/02), I am in the process of making a vertical axis, to 
work with the x-y axes I've already made. It will be similarly simple,
easy, and inexpensive. I had a piece of countertop lying around, 36"x30",
on which I will mount the completed x-y machine. Then, a third (8.5" 
dot-matrix) printer's carriage assembly will be mounted, on a type of 
gantry, oriented vertically over the center of the x-y system. I was going 
to make the stationary gantry out of a similar piece of countertop. But, 
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for me, it seems quicker and easier to just use threaded metal pipe to 
make an "L"-shaped support, over the x-y machine. (And, as can be seen
in the photos, I still need to construct a platform on the smaller printer's 
printhead assembly, to hold the actual workpieces. It will be made of 
small aluminum channel and bar stock, similar to that used on the larger 
printer's printhead frame.)
IBM Proprinter (8.5-inch) Carriage Assembly, mounted on threaded
pipe support:
3-Axis Unipolar Stepper Driver Circuit, on proto-board:
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To be continued...
Questions or comments? Email Tom Gootee at tomg@fullnet.com.
New alternate email address: tomgootee@yahoo.com (Use only if 
you can't get through via tomg@fullnet.com.)
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