Re: [CAD_CAM_EDM_DRO] Before I make a mistake, what do I need to know?

> I am a new member to this group, and also new to CNC, so I need a lot
> of help. I have 3 Sanyo Step-Syn Stepping Motors, Type 103-820-2,
> which are 4.5V, 1.4A, and 2 Degree/Step.

Ah, IBM printer motors ;-) Not very powerfull, but they should work
for a small machine and low traverse rates.

> I have been searching and reading material on the net, and I am still
> not sure about some things.
> What I want to do with the motors is to build an all metal (aluminum
> frame) CNC drilling (for printed circuit boards) and routing unit.
> With the motors that I have, is it best to use them as bipolar rather
> then unipolar motors which they are, just by not wiring to the center-
> tap of the coils?
> I am still unsure about stepper motor controllers. Is it best to
> purchase a commercial controller or will a DIY one be adequate. I
> want to power the motors with 24VDC-35VDC and use a "chopper" type
> circuit. Also, there are different circuits for unipolar and for
> bipolar.

I would be tempted to run these motors bipolar, using half the coil
(center tap to one end). If you use the full coil, the inductance
will be too great. Normally, for a 4.5v coil you would want a chopper
supply much greater than 35v, in order to be able to switch it fast,
but that is about the limit for the cheap integrated drivers.

I'm guessing these motors are NEMA 34, and physically standard in
about everything except their 2 degree step and maybe shaft size.
What I'd suggest is you build mounts for these motors with the idea of
later putting on more powerfull motors that have the same faceplate,
but are longer. (You will have to change your software to handle
standard 1.8 degree steps when you do that, too). Also, make
allowances for switching to a standard 3/8" shaft if these are a
different size.

Anyway, you can run these existing motors (slowly) off a 35 or so volt
supply with one of the L297/L298 2 amp bipolar chopper driver kits.
This will give you some experience with driver circuits. If you later
go to bigger motors, you can try to build a driver with discrete
MOSFETS or simply buy the popular Geckodrive modules.

> Also, originally I had thought of just using a Dremel tool for the
> drilling of small holes into printed circuit boards, but now I think
> that the Dremel will be too light, especially if I want to do some
> routing in wood. What would be a better choice in a high speed tool
> to use...a higher HP router or a high speed laminate cutter?
> What are the other things that I should think about in the design of
> this unit before construction is actually started.....besides money :)

Start with the dremel if you have it, design your Z axis to be able to
optionally carry a laminate trimmer or a sherline headstock.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT