Rotary table conversion?

C

caddy

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Just wondering, I 've been keeping an eye out for a 4th axis rotary table for my cnc mill but they are "crazy" expensive. Has any one made an adapter for a manual rotary table and used a stepper motor to achieve this? I'm told the expensive ones are expensive because they have no backlash issues. I realize that a manual table might have some but since I'm not building rocket ships, I can live with some.
Most of what I would do is not high tolerance stuff, mostly engraving and the like.
I would like to get some feedback from someone who has tried it before I try and do it.
Thanks.
caddy
 
I have a article in the cnc version of home shop machinist from 6m ago or so where they did it. Back lash can hurt a project if it's bad enough while doing the right thing. Try to keep in moving in one direction. If it would even be bad enough to worry about, I dont know
 
Most of the better rotary tables have adjustable backlash. The worm is held in cam bushings and can be set further into gear. Mine is an old Yuausa 8 inch and I can adjust it to about 0 lash. Connecting a stepper motor is just a matter of building a bracket, and a connecting coupling. One of these days I'm going to convert mine. I want an encoder to read the table position rather than rely on the motor position , so I'm still trying to figure out the best way to do that. With the encoder reading the actual table position, there is no backlash issues unless the system is really loose.
 
There was a thread on another forum about this. It got ugly and there wasn't a lot of detail about it. But, mentioned above, adding a stepper is fairly easy. This is the place that the person in the other thread bought his table. Evidently, these are the same/similar to the ones sold by Tormach, except without the motor.

http://www.utoole.com/servlet/the-Rotary-Tables-,-Dividing-Plates-fdsh-Heads,-Tailstocks/Categories

I have the 8" from Tormach. I've got no idea how to use it, but it's a pretty nice piece. It leaks oil fairly readily, however. Evidently, this is common, so common that instructions are mentioned in the manual how to handle it.

I suppose when buying, it might be a good idea to ask about the backlash, or if it's adjustable.

Eric
 
Caddy
on the one I did in post 111 and another one just like it I did for a friend the housing the motor mounts to rotates from engaged to a neutral position and that is the backlash adjustment. when you rotate it to full engagement there is no backlash. before mounting the stepper I attached a drill to the shaft and just left it running until it was very smooth. after I did that when I tightened the backlash there were no spot tighter than another and it runs really smooth. I'm sure they just cut the gears and put them in, a little break-in made a big difference.
Steve
 
Something like this?
I just made up a block which contains a shaft coupling to go between a convenient flange on the rotab and fits the stepper flange and locating spigot. The screw head on the side is a cover for the Allen key to tighten the grub screws on one end of the coupling.
Works brilliantly. This one is a stand-alone digital divider but can also run continuously at 5 speeds.

15012012601.jpg
 
I'm looking at something similar myself. Seems pretty straightforward to me. Either use a coupler and mounting flange or run a timing belt and fit the motor on the side of the table somehow. Heck, you could interdependently bolt the motor and table down to the mill table as long as you made sure the belt was tensioned and aligned. Come to think of it, this might actually be the easiest and most flexible approach....
 
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