Backlash free rotary table

[Zoidberg]

I want to build a rotary table that can handle continuous milling!
Do you think my drawing would work?
The upper gear belt pulley can rotate freely on the axle, and is connected to the axle via the spring, and is preloaded.

[RICHARD ZASTROW]

As an alternative, "google" Howimat. This concept is ball driven like a ballscrew in the round.

Dick Z

[Zoidberg]

I will check it out! I have also been thinking of using 2 servos and do the preload eletronically with a µC

[BillTodd]

Looks like it would work to me, although mixing gears, lubricant and timing belts might be a problem.

How about placing the two worm gears at an angle to each other, driving one directly and the other via a bevel gear? (if you see what I mean)

Or...

What about a buying or copying Commercial anti backlash worm drive ?

[Zoidberg]

Hmm, thats an interesting idea! I'll make a drawing!

[Zoidberg]

I made a drawing and realized that the worms would need to rotate in the same direction in this configuration :P

The dual servo version seems more and more appealing!

[BillTodd]

Just swap the main-shaft bevel gear to the front of the perpendicular one.

[BobWarfield]

There are a lot of commercially available low backlash drives on eBay. Search for "harmonic drive" or "bayside drive". One of those sure will least trouble and expense.

Another possibility is to preload the heck out of your rotab drive with another gear and some bellvues. Not sure how much torque you plan to put on it though.

People also run 2 of the main circular gears spring loaded to spread the teeth just enough to get rid of the backlash. In this case, you'd make the spread adjustable with a threaded screw.

These last two solutions seem prone to binding and wear.

I would be tempted to also consider a big timing belt drive. properly set up, you'll get minimal backlash. People are even using these for linear motion with good success.

For really high torque situations, you might still find a brake is useful. Slew the 4th axis to the desired position, send an M-code to lock the brake, cut, and unlock. Small disk brakes from everything from mini-bikes to lawn tractors are readily available and work with an air over hydraulic and solenoid valve.

Cheers,

BW

[Zoidberg]

Aaah yes...

[mc-motorsports]

Harmonic Drive is the way to go, if your willing to spend a little money.

http://www.powertransmission.com/iss...6/harmonic.htm

[BillTodd]

Originally Posted by mc-motorsports Harmonic Drive is the way to go, if your willing to spend a little money. http://www.powertransmission.com/iss...6/harmonic.htm

Or the seeking tooth variation:

[Zoidberg]

I want it to be able to use it for continuous milling, like gear hobbing and milling springs, not just indexing!

I think it's best to have the worms axially stiff because they can't be backdriven. So if you just can keep both worms in contact with the gear teeth with a little rotational preload it should be backlash free and much stiffer than the version with axial preload of the worms or split wormgear!

Harmonic drive seems nice! But i like to design and build stuff more than paying for complete solutions

I was thinking of a gear belt drive at first.. but it's a little impractical when you want 1:100 ratio or so..