Re: [CAD_CAM_EDM_DRO] Re: run two geckos from same pins

In a message dated 11-Jan-02 13:28:20 Central Standard Time,
signworks@... writes:

> Back to your XXYZ cnc router, it would be great to to run a timing belt
> across both X axes (even though you have 2 motors with 1 or 2 controllers),
> just to keep them both honest (because steppers are <usually> open loop
> systems

I have noted this thread with some interest, and I guess I SHOULD throw in my
own experience; isn't that what this group is all about? In '85, I built a
rather large "X-Y Table" (router) for an English firm. They use this to
route/plane/slot pipe-organ windchests (sorry! In England, they call those
things "soundboards"). As the "Y axis" spanned a 6" wide table, I felt that
driving that wide a carriage from only one of its ends via a single "X
lead-screw" would introduce "angular distortion", so, I put an (expensive!)
1.5" dia. ball-screw (with preloaded ball-nuts) on both sides, and connected
these together and to a single large stepper-motor (MO-172) with #35
sprocket-chain. This worked, and rigidity seemed optimum. I got the machine
installed and flew back to Texas.

Well, the next time I saw this machine was 15 years later, and they had
removed one of the LONG "X screws", all the chain and sprockets, and had
cobbled a new mount for that large stepper, so it could drive the ONE
remaining X-screw, through a flex-joint. They told me this worked fine, as I
had built the steel frame so rigidly in the first place, and it was NOT used
for metal-working, after all, so the one lead-screw was sufficient.

Oh, one of their "old guys" who had been with the firm for thirty years told
me it "Was not your fault, as we run the thing 20 hours per day, six days a
week, so, it's paid for itself and the mod's many times over!" Whew. AND,
he said the bicycle-chain gave out in the first month. Just NOT sturdy
enough for the application. And, they had at first repaced all the sprockets
(several idlers to "hold up" the chain!) with toothed "timing-belt sprockets"
and rubber timing-belt. This, they thought, at first, might outlast the
bicycle chain. NOT! It was much quieter, of course, but gave out rather
right away, making that an expensive lesson in "build-it-yourself".

Still, this home-brew machine is still working with most of the original
paint (Grainger's 'machine-green'!) and Superior Electric steppers. Oh, the
original electronics became discontinued just days before THEY crapped-out,
so... Moral: If you aren't a vast, professional CNC-shop, don't be so bold
as to offer a $10,000 machine for a customer across the sea, unless you enjoy
nibbling fingernails and contemplating the joys of stomach-ulcers! (knock on
wood!)


[Non-text portions of this message have been removed]