Finding a 4th axis servo?

[lilricky2]

I have an Enco 2 hp mill converted to a 3 axis cnc mill. I have Reliant 1/4 hp servos driving each axis. I have been using my 6 inch H/V rotary table quite a bit lately. I would like to go ahead and add a servo motor to the rotary table so I don't have to stand over the mill and crank on the it by hand. I'm sure you've guessed that this is tedious, and makes me very tense. Not to mention that it forces me to keep my projects fairly simple. I use mostly carbide tooling and flood coolant. How do I spec out a servo for the rotary table? Will I need one with a built in brake? What kind of torque am I looking for? I know my current servos are probably overkill, but since I was much greener than I am now, I figured better safe than sorry. My drives are Gekkos and I am currently running Bobcad V20 and an older version of Mach2. I mostly cut gun parts, sights, muzzle devices, flute barrels and I am learning to machine checker frames. Most of the parts, with the exception of rifle barrels, will fit in a 4 inch by 6 inch working envelope. I appreciate any advice/suggestios on specs, brands, where to buy, how to set up, software, any of it.

Thanks,
Rick

[lilricky2]

Anyone????

[BobWarfield]

Shouldn't be too hard to track down some articles from others who have done this. I would think a NEMA23 frame stepper motor would work fine. I've yet to see a homebrew that had a brake. John Stephenson has good photos of one he manufactures and sells over on the HSM board.

The commercial tables do have the ability to lock the axis. This can be especially important as you cut more and more off axis. As I understand it, their idea of a brake is similar to gear teeth: one set on the rotating part, one fixed to the chassis. To lock, bring the teeth together with an air cylinder.

One other consideration is backlash. Rotary tables all have appreciable backlash. If you need to get rid of it, the best solution I've seen is to use a harmonic balancer. Widgitmaster built one such 4th axis and photographed it for this web site, so do a search to find it.

Best,

BW