Advice on 28" Rotary table drive design

[Jim Dawson]

The theoretical rotational accuracy of the system using the flex plate (164 tooth) and a 10 tooth pinion and 10 microstep is 0.011° this equates to a cord length of 0.003'' at the circumference of a 28'' dia circle.

I maintain that it is possible to achieve zero backlash in the gear train using a stock pinion, possibly requiring some OD reduction of the pinion. If I am wrong here, I will build a zero backlash pinion that will work, at no charge.

[mactec54]

The theoretical rotational accuracy of the system using the flex plate (164 tooth) and a 10 tooth pinion and 10 microstep is 0.011° this equates to a cord length of 0.003'' at the circumference of a 28'' dia circle.

I maintain that it is possible to achieve zero backlash in the gear train using a stock pinion, possibly requiring some OD reduction of the pinion. If I am wrong here, I will build a zero backlash pinion that will work, at no charge.

And it will be like a concrete mixer turning, it has to be smooth for 3D printing

The teeth on these ring gears are not even a true gear tooth profile, are not designed to be used as a gear as such,you should consult with gear manufacturers on how to do this to get zero backlash, I'm sure they would be all ears, without a split spring loaded pinion or gear, it is not possible to have zero backlash, if it was everyone would be doing it

The problem is with that gear ratio, and if the stepper is using 10 microsteps the motor won't have enough torque to drive it, or if it does won't be able to control it very well

[Al_The_Man]

I have some surplus Emerson precision Planetary GBoxes of various ratio's but I think they would be a bit heavier duty than you need, but they are a nice way to go!
Max.

[Jim Dawson]

And it will be like a concrete mixer turning, it has to be smooth for 3D printing

The teeth on these ring gears are not even a true gear tooth profile, are not designed to be used as a gear as such,you should consult with gear manufacturers on how to do this to get zero backlash, I'm sure they would be all ears, without a split spring loaded pinion or gear, it is not possible to have zero backlash, if it was everyone would be doing it

The problem is with that gear ratio, and if the stepper is using 10 microsteps the motor won't have enough torque to drive it, or if it does won't be able to control it very well

We could argue this for a week with no resolution, so we will just have to agree to disagree. Suffice it to say that I have made a successful career out of doing the ''impossible''.

[Al_The_Man]

Suffice it to say that I have made a successful career out of doing the ''impossible''.

Yeah, miracles take a little longer.
Al

[mactec54]

I have some surplus Emerson precision Planetary GBoxes of various ratio's but I think they would be a bit heavier duty than you need, but they are a nice way to go!
Max.

He already has some heavy duty parts for the center hub so your gear boxes would not be out of place if the ratios where low enough

[Eldon_Joh]

Two automobile starter pinions on the flex plate, with the backlash taken up either mechanically or with a spring should work fine and provide smooth motion for OP's needs.

Regarding the gear teeth on the flex plate.. they are good enough. at 164 teeth you almost can't tell the difference between a gear tooth and a rack and pinion anyways. the gear teeth are broached, all at once btw, so i assume the broaches are generated on gear cutting machines but perhaps not.


btw if you need a cheap rack and pinion, grind the welds off the flex plate and cut the gear and bend it straight. you probably want to temper it again at 500F afterwards, or bend it while its hot.

[disneytoy2]

Thanks all! So much great advice. And I appreciate you thinking out of the box.

[mactec54]

btw if you need a cheap rack and pinion, grind the welds off the flex plate and cut the gear and bend it straight. you probably want to temper it again at 500F afterwards, or bend it while its hot.

That's the most ridiculous thing you have posted

If you where to straighten out the ring gear, the teeth would close up, and there would no way be able to keep it in pitch

A piece of rack that size would cost around the same as a flex plate

[spumco]

I've been following this interesting thread, especially since I'm at the beginning of a build using a Bell-Everman loop-track type of system.

If the starter & flexplate doesn't work out to satisfaction, maybe buying a T5 belt and bonding it inside out to a disk of some sort would work. Turn the disk OD so the belt is a snug fit and glue it in place. Make a couple rims for belt tracking (i.e. sandwich) and then get a larger belt that loops around the disk and a small T5 pulley on the stepper or servo. An idler pulley to ensure more tooth engagement on the motor pinion and belt tension.

A 28" turntable works out to about a 450 tooth 'pulley' if my math is anywhere close. Brecoflex recommends 30T minimum pinion (with idler backbending), so that works out to 15:1 reduction. If you need more, use a double-reduction and switch to a GT2 profile for the primary reduction pulleys to minimize backlash.

A 450T belt is about $17 from B&B, and figoure about $20 for a longer one to wrap around the pinion. Plus the pulleys and GT2 stuff if ou need double reduction.

I think this would be quieter and smoother than the gear arrangement.

I seem to recall Mke Everman mentioning in his huge thread that the trapezoidal tooth profiles engaged each other better then curvilinear in a belt-on-belt situation.

[Eldon_Joh]

That's the most ridiculous thing you have posted

If you where to straighten out the ring gear, the teeth would close up, and there would no way be able to keep it in pitch

A piece of rack that size would cost around the same as a flex plate

a flex plate is like 10$ at a junk yard.

as for how much the teeth close up, not enough to matter. yes i know this from experience.

regarding ridiculous things you post, telling someone incorrect parameters burned up their spindle when it worked for them.. for 2 years! is pretty funny.

[mactec54]

a flex plate is like 10$ at a junk yard.

as for how much the teeth close up, not enough to matter. yes i know this from experience.

regarding ridiculous things you post, telling someone incorrect parameters burned up their spindle when it worked for them.. for 2 years! is pretty funny.

Are yes but if they had the correct Parameters it would not of burnt up, if your spindle has burnt up and it could of been avoided, that would have very little to do with funny

[Al_The_Man]

He already has some heavy duty parts for the center hub so your gear boxes would not be out of place if the ratios where low enough

Various from 5:1 to 100:1, various duty ratings.
Al_The_Man