Re: [CAD_CAM_EDM_DRO] Re: Gecko + Servos + Taig Mill

lasernerd@... wrote:

> I thought that sounded a bit on the low side. The Taig is a small
> machine, and you can't expect too much out of it (although it is much
> more rubust than a Sherline).
>
> I just ran downstairs and did some tests. The Taig seems to like
> 5400RPM with a 3/8" cutter on 6061-T6 aluminum. I was taking 0.1"
> depth of cut, with ~40% of the diameter cutting, and was craking as
> fast as I could, about 0.2"/second, 12IPM. At this rate, it was
> almost like craking without cutting anything, so there was very
> little force. However, I'd like to have lots of power under the hood.
>
> The motor I'm using is a 1/5 HP, 1725 RPM with pullies. Max spindle
> RPM is 5400, min is about 500 IIRC. Max cutter diameter will be 3/8".
> The max X travel is 8", IIRC, and the max Y travel is 5.5". I would
> like to have about 100 IPM rapid feed. The max workpiece weight
> should be about 10lbs, although probably not even that. Right now,
> the leadscrews are 1/2-20, but I'd like to replace them with
> ballscrews. Probably with a 5TPI pitch. I will be cutting everything
> from wax to stainless steel.
>
> If anyone can suggest a size (# of watts, holding torque, etc) of
> motor, I'd be quite open to comments. Where does one look for motors
> on the surplus market? Is it possible to just buy an appropriatly
> rated DC motor, and then add my own encoder?

Yes, in principle. The only possible problem is that some motors
not designed for servo use may have a lot of 'cogging' or torque/speed
ripple. That is not desirable for slow servo motion control.

> Seems like it could be
> cheaper. I'd like to use the Gecko, so where can I find compatable
> encoders?

Most any encoders that run off 5 V, and many that run off of 12-15 V
will produce TTL signals. Look on eBay. One thing to note is that encoder
specs are not totally consistent. CPR could mean cycles/revolution or
counts/revolution. A 1000 cycle/rev encoder will produce 4000 quadrature
counts / rev. Make sure you know the resolution of the encoder before
you buy, a 100 CPR encoder (of either interpretation) is not going to
be much good, especially with the 5 TPI screw.

Jon