[Coco] [color computer] CNC with a Coco

[Gene Heskett]

On Sunday 22 July 2007, George's Coco Address wrote:
[...]
> I no longer work at that sweat shop. I'm now back in the construction
>equipment rental business and making six smackers an hour more. Yeah!!
>
That's the ticket!

> I'm about to buy another lot on the east end of my property, so the
>increase in pay is VERY welcome. Soon, I'll be able to build a real shop to
>play in.
[...]
>mods can actually do that, donbesilly.
>----------------
>
>Gene, even if the coco could do that speed, the machine can't. Not enough
>power. The coco can actually drive the steppers as fast as the machine can
>grind. So speed isn't an issue until I build a mill with more power. The
>issue now is the software.
> I've learned a lot working at the machine shop and the stuff that those CNC
>machines are capable of is mind boggling.
>
> The coco can step the motors just fine. However, doing the math to
>determine the steps of the motors takes a long time.That's the bottleneck in
>this project.

I'd imagine.

> To do a simple four inch circle, with resolution of 12800 steps/inch takes
>about twenty minutes. I placed an ink pen cartridge in the dremel and drew a
>circle with that. I think I may have gone into a coma waiting for it to draw
>that circle.

:-)

>  My original intent for this machine was to make tiny parts and this hasn't
>changed. I think it will work fine for making tiny parts. I really believe
>this.
>
> When I need to make engine blocks or cylinder heads for my Ford truck, then
>it just won't do it. A small gear or sprocket to fit a small steam engine
>should be a piece of cake, if I can get the software right.
>
>  This mill can repeatedly move to within .0005 inch (more or less) to the
>designated position. My test indicator only promises .001 accuracy. Heck,
>that's close enough for me.

Me too.

>  Of course, the coco and the math says it's within .000078125 inch. Your
>Harbor Freight and my Northern Tools mill/lathe  won't even consider this to
>be attainable.
>
> I'm lucky if I can turn a part within .001 on my lathe. Even luckier if I
>can mill the Z axis within .030. However, I don't even try to make tiny
>parts on that machine.

I replaced the z axis screw on mine with a 1/2" 10 tpi acme with two nuts to 
adjust the backlash.  But the head itself rocks a teeny bit on a direction 
reversal, limiting how well I can compensate the backlash in software.  If I 
always move the z in the same direction during the cut when making 3d parts, 
its well within a thousandth.  Do a reverse at the top of a crown and you can 
catch a fingernail on the ridge. :(

But ISTR you are using a Dremel grinder, and its spindle accuracy is so bad 
there is no real use trying for .001" accuracy.

As for that lathe, 2 or 3 thou at best, the carriage fits the ways way too 
sloppily.  Not to mention the tailstocks height is off about .020" even if 
set for min taper on a long turn supported at both ends.  Correcting for that 
make life very confusing.

> As for micro-stepping, yes, a coco can do that to 1/1600th of a turn using
>all eight bits from the data latches I've put on that coco.

The xylotex amps do that 8 microstep thing internally with nothing but a pair 
of step & direction lines as input, 2 bits.  The d/a's for coil currents are 
internal to that driver chip, one of Allegro's 39xx family.  Now if it could 
take 2x the voltage and 2x the current, the machine would fly, as is, about 
20 ipm on any axis has the steppers pretty close to tapped out.  So I don't 
try for more than about 10 ipm max if I don't want to skip steps.

>It's just 
>hardware/electronics. However, it would take years for the software to draw
>that circle if we attempted that. What I need is a coco with at least a
>100mhz clock. Then I can make more mistakes in less time.

Yeah, me too.  At 1600mhz, I can make a lot of mistakes (& junk parts) in 
record time with mine. :(

> With 400 steps per turn and a 1/32 inch pitch on the lead screws give me
>12800 steps per inch. The lead nuts are Teflon and really tight, about an
>inch long. So there isn't much room for slop. The steel in the frame of the
>whole setup will flex more than the lead screw/nut assembly will slop. I'm
>not disappointed with it.
> The X and Y axis both have six inches of travel. The Z axis has about four
>inches travel. This should do nicely for making parts no larger than about
>an inch. The next step, after I get these three axis working correctly, is
>to make the 4 axis. The 4 axis is going to be a rotary table that can turn
>the part(for making gears). At 400 steps/turn and a worm gear, the
>possiblilties are limitless, except for the time it will take the coco to
>turn it. Now it's to the point that I can make a gear in about three hundred
>years. But, it will be a perfect gear.

Yup. that's my next step too, getting a motor on the table.  I bought a 4"er 
the last time I came past the Grizzly store up in PA.  Very poorly built IMO, 
but it does work.  OTOH, it was only a big buck too.  It has managed to 
sharpen a couple of broken carbide bits fairly well though.

> Coco lives! PCs die.

No, PC's running winderz die.  Running linux they're fine, cuz they are doing 
what YOU want them to do, and NOT what Bill might want them to do behind your 
back, like phoning home with the contents of the firefox password file, 
including all your bank numbers...

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Maintainer's Motto:
	If we can't fix it, it ain't broke.