[Coco] [color computer] CNC with a Coco

[Gene Heskett]

On Sunday 22 July 2007, George's Coco Address wrote:
>Well, dogonnit!
>
>
> As I proceed with this project, I find that some things just won't work.
>Actually, it will work, but not as I want...
>
> The X/Y axis were originally on the same table. As I progress with this, I
>found that it is difficult to keep the chips out of the top axis(Y axis).
>The X axis is okay. The plate is large and able to contain chips and coolant
>(if necessary). However, the Y axis was originally on top of the X axis and
>was vulnerable to to chips, got in the way and just plain wrong.
> So, I decided to rebuild the Y axis to be on TOP with the Z axis(I'll move
>the head both Y and Z . This way, they won't have to deal with the chips or
>coolant as they will be above the work piece.
>
> I was digging around in my arsenal of stuff and found that I have a total
>of three, 24 volt NEMA 24 type steppers to do this whole project.
>Originally, I had a mix of three volt, twelve folt and twenty four volt
>steppers.. I built a new driver board with chips designed to do this and now
>it's starting to look pretty good..
>
>  I hope I get this project done before I die of old age.
>
>
>Gene,
>
> I know this would be easier if I used more moderen hardware and a more
>modern computer, but this is fun doing it with a coco.
>
> It's slow and cumbersome but, this is my project.
>
> Once I make my firat part, I'll probable toss the whole idea and go with
>the PC and other stuff.
>
>But
>
> I HAVE TO DO IT ON A COCO FIRST!
>
> It's a coco thing.

:-)  That it is George, that it is.  There is a certain cachet to be able to 
say you did it with the coco.  But, there is no way the coco can drive 3 
axis's at up to 30,000 step/sec, or turn a nema 22 motor .01 rpm using an 8 
step microstepping drive amp, doing it so silently you don't hear the stepper 
at all, when a single step is 1/1600th of a turn, and keep track of where 
every motor is so they all get to the end of the move simultainiously.
I can tell emc2 to move from -1"x, to +3"x, -5"y to +_2"y, and 0z to -3" z, at 
the same time and the cut will be well within a micron of a straight line 
electronically.  Now if you think my little harbor freight mill, even with my 
mods can actually do that, donbesilly.
  
That said, my end of the week project was caused by the replacement of a 50 
year old one and 3/16" fafner ball bearing on one end of the main blower 
shaft in the transmitter about 6 weeks ago, with a fresh one.  The shaft was 
fine then and everything ran very quietly, for about a week.  Then the 
eccentric nose on the bearing broke away and allowed the shaft to start 
walking in it, wearing the shaft a thou or 2 before we could get a 2nd 
bearing in it since it runs 24/5, 20/1 and 22/1.

Now the whole thing rumbles and wobbles and will eventually fatigue crack the 
steel plating on that end of the blower housing if we don't do something, 
like figure out how to shim the shaft back to size yadda yadda.  Our maximum 
downtime in a week is about 4 hours in oone piece, so getting the shaft 
sprayed and machined back to size is not an option.

We found a 6" x 50" roll of stainless shimstock .001" thick, and while I'm 
trying to imagine getting that in and suitably permanently placed, it 
occurred to me that the shaft was fine between the bearing and the 
taperlocked pulley 3" away, so why not just move the bearing off the worn 
spot?

So this last 2 days project has been sawing a 2.05" thick piece off the end of 
a 5" square block of alu about 2 feet long I found at the scrap yard a couple 
of years ago, trading a 50 dollar bill ($1/lb) for it at the time.  I did 
this on my 12" craftsman bandsaw with a 1/4" blade in it, cuts alu just fine 
although slowly as you can imagine. 15 minutes maybe.

Clamping it down to my micromills table, I faced it flat top and bottom, 
located the 5 holes, center one for the shaft and the 4 bolt holes in the 
corners and drilled them (a drill doctor sharp drill bit will drill anything, 
they are an amazing sharpening tool) but only drilled the center one through 
at 1/4" so I could locate the center from the other side when I had to turn 
the thing over just by setting the bit into the hole & clamping it down.  No 
way that micromill, or a 1/4 carbide bit would reach all the way through that 
2".  Heck the bit had been broken and resharpened by me once, so it was a 
little short.

I had to write the gcode to bore that 1.475" center hole, and each side of it 
was about 4 hours for my little mill & the air compressor to blow swarf away, 
but its done and ready to install.  This might have been, after setup, a 3 
minute job for your work machine to do, but again, just because I could.  On 
a 300 dollar harbor freight micromill I put 262oz motors on, driven by a 3 
axis xylotex amplfier & an old pc running kubuntu-6.06 linux.  If I live long 
enough, one of those $1300 grizzly's with some 425 oz motors will eventually 
take its place.  If I live long enough...

Now I have to install it next weekend.  For you on your day job, piddly, for 
me, big deal.  Makes me grin from ear to ear just thinking about it. :-)

-- 
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)
Flon's Law:
	There is not now, and never will be, a language in
	which it is the least bit difficult to write bad programs.