After playing with rotary tables for a week now, I have had it.

Could a cnc rotary table be simplified into its most basic components?

My idea it to simply make a metal stand with a hole through it. Insert a steel rod and thrust bearings in the hole, attach a chuck to one side of the rod and a pully wheel to the other where the servo will drive it.

If the servo has a decent turn ratio like 10 to 1 there should be ample torque to keep the chuck steady, right?

I doubt it. The forces produced by milling and drilling metals are high. But, if you are only engraving, then it might work.

But, if you can conjure up some kind of handy air brake to apply to the backside of the platter (which will also stabilize it), and you only index while the tool is clear of the work, then it may serve your purpose for actual milling ops.

what size servo? I agree with HuFlungDung that it probably will not hold for milling material. If you are only milling slots or some other linear movement along hte X axis, and somehow have a way to put a solid brake on the piece, it should be okay (assuming construction of hte using is rigid enough). Have a look at what Widgitmaster did in his thread. You can get a harmonic drive up to 160:1 gear reductions, THAT will be enough torque to hold it all :).

What's the problem?

Phil

After playing with rotary tables for a week now, I have had it.

The problem is with the rotary tables worm drive. In order for there to be no backlash, the gears need to be tighter than the servo can turn.

Depends how bad things are but it is possible to lap the worm and gear together, although zero backlash is not really possible, you need some space for lubrication. What backlash do you have and is it the same at different points around the circumference.

Regards
Phil

The problem is with the rotary tables worm drive. In order for there to be no backlash, the gears need to be tighter than the servo can turn.

This might be a bit late but check this out:

http://www.deepgroove1.com/4thaxis.htm

They also have some other interesting fixturing and acessories

Maybe look at this thread. http://www.cnczone.com/forums/showthread.php?t=19448&highlight=harmonic+drive

I don't know the details but I think it's a pretty good performer.

I just made a very basic 4th axis based on a Taig headstock and a 200 oz/in stepper
it will probably last longer if I add some support to the worm
Mark

metalbyter, have you had problems with chips going into the worm gear? Do you have a cover for the gears so this does not become a problem? How did you decide what ratio/threads to use, it looks really efficient!

No I haven't had a problem with getting chips in the gears yet but I probably will cover them up. There is more on the 4th axis on my web site WWW.microtools.ca
Mark