Les, I can achieve .001" (linear table motion) steps fairly easily with steppers.
Depending upon the toothed drive belt, I would assume the precision would be at least as good as +/- 0.0001"
Is this good enough for PCB's, even with (the larger) surface mount pin spacing?
Best, Charlie
PS: wowzer, that linear rail link from ebay you gave is a knockout!!! And only 10 pounds...that's a deal, in my book. :)
--- In Homebrew_PCBs@yahoogroups.com, Leslie Newell <les.newell@...> wrote:
>
> Hi Charlie,
> > I can save a serious chunk of dough making the 3D ... maybe even 4D rig myself, with surplus steppers and my own circuit boards from scratch...
> >
> Yes, it isn't difficult. Preferably you want to use ball screws for the
> drive. Acme screws will work but any backlash will cause problems. HTD
> toothed belts can also work quite well. Don't try allthread rod. It
> isn't worth the hassle.
>
> Don't use rails that are supported only at the ends. There are a lot of
> machines out there that have round rails that are only supported at the
> ends. In the middle of their travel they flex and bend all over the
> place. It is amazing how much even a thick rail will flex. Linear rails
> like these
> <http://cgi.ebay.co.uk/Bosch-Rexroth-linear-bearing-70-mm-rail-R044281301-/170525543558>
> are the best but they are pretty expensive. You can achieve pretty good
> precision using ground flatstock (tooling plate) and skateboard
> bearings. The biggest problem with that setup is keeping the dirt out.
>
> I would suggest that you buy the stepper drives rather than trying to
> make your own. Microstepping drives are much better than full or half
> step. If you want maximum dependability and reliability, look at servos.
> They are a bit more expensive but they are worth every penny. IM Service
> do some nice motors and drives for reasonable money
> <http://www.imsrv.com/>. If you do go for steppers, get the modern
> square type, not the old fashioned round type. The square ones work much
> better.
>
> > and spend the money where it really matters: the spindle itself. Something ridiculously fast with close to zilch run-out.
> >
>
> There is an interesting discussion of cheap Chinese spindles on the Mach
> Yahoo group at the moment.
> <http://groups.yahoo.com/group/mach1mach2cnc/>. For your application you
> don't need more than about 150W but a bigger one, say up to 800W would
> be fine.
>
> > Thanks for all the links and tips; this is soooo the way to go, I'm never looking back at etching again...just gonna use the protoboards that match up to breadboards until I get the PCB milling rig done, and then convert straight to milling. (routing).
> >
>
> Routing isn't a magic bullet. It solves some problems but it has it's
> own steep learning curve and problems. However a CNC router is a very
> handy tool to have anyway. If you are into model making etc you will
> soon wonder how you ever did without one.
>
> > My God, I can't even imagine .005 run-out! They actually make spindles that bad?
> >
>
> Oops, not enough zeros. I meant 0.0005" :-[
>
> > Just to theorize a little....it did just recently occur to me that this could also be done by using, instead of a rotating spindle with a V bit and drills, a very fine, very high speed/pressure jet of abrasive...either air based or water based. I know such things are made....I remember reading of one that had a diamond head, because the jet of water that came out was under such high pressure and at such an insane speed it cut through inch steel plate like it was butter...soft butter.
> >
> > Now, THAT would be a fast method. In fact, the table would have to move FAST to keep the jet from just boring right through....heh heh heh...but it could be done, no doubt about it. I'll have to google if there are any micro-jet rigs/heads for such a thing. And incredibly fine abrasive.
> >
>
> Waterjet is quite impressive. I have seen it cut through 2" steel plate
> using garnet abrasive. Cadbury's Crunchies (A sweet made with foamed
> sugar covered with chocolate) are cut out using an oil jet.
> There are a few problems with jet cutting. The first is the pressure
> needed. Waterjet uses BIG pumps (15hp - 200hp), running insane pressures
> (40,000 - 90,000PSI). The other difficulty is in maintaining the correct
> cut depth. Copper is harder to cut than fibreglass so the feed rate
> would be ultra critical. You will have major problems on corners as the
> machine slows down to take the corner. Also as the nozzle wears you
> would need to tweak the feed rate to compensate.
>
> Les
>