Advice on 28" Rotary table drive design

[disneytoy2]

Hello Gang!

So I'm getting close to building the 28" round base for my Printer. This is a 2 meter tall clay printer. The base is 28" using a Ram 3500 Wheel Hub assembly. Very heavy duty. Now I need to give it rotation. I have 2 options.

1) Large pulley and belt. I don't need speed. and it will most likely never do more than 1 rotation. So major gear reduction.

Second, I thought about using the splined center hub. If I can find a cheap/used stub shaft, I'd need to adapt a smaller shaft that can key into a Worm Gear. I can drive this with either a nema 23 or 34 stepper.

Please see my diagram.

i like the elegance of using the intended shaft to rotate the machine.

I'm just not sure how much torque I need?

Is there any difference between the toque generated from a worm gear or from the belt and pulley?

Any suggestions appreciated!

Thanks

Randy

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[Jim Dawson]

Hello Gang!

So I'm getting close to building the 28" round base for my Printer. This is a 2 meter tall clay printer. The base is 28" using a Ram 3500 Wheel Hub assembly. Very heavy duty. Now I need to give it rotation. I have 2 options.

1) Large pulley and belt. I don't need speed. and it will most likely never do more than 1 rotation. So major gear reduction.

Large pulleys are expensive. One way around this might be to use more automotive parts and use gears. An automatic transmission flex plate has a large ring gear on it and they are pretty cheap. Then you would have to use a mating gear from a starter. Due to the design of the starter gear, it would be easy to adapt to stepper motor. Not sure what the gear ratio would be, but I suspect it would be at least 15:1 maybe more.

https://www.ebay.com/itm/Sbc-Bbc-Che...183a:rk:4:pf:0

https://www.ebay.com/itm/ACDelco-198...6bMr:rk:9:pf:0

Second, I thought about using the splined center hub. If I can find a cheap/used stub shaft, I'd need to adapt a smaller shaft that can key into a Worm Gear. I can drive this with either a nema 23 or 34 stepper.

Please see my diagram.

i like the elegance of using the intended shaft to rotate the machine.

That would make a nice compact system, but there will be some backlash in a standard worm gear type gearbox. The shaft adapter would be easy to build if you have access to machine tools.

I'm just not sure how much torque I need?

If you used a 15:1 gear box it would provide plenty of torque for anything you want to do with just about any motor.

https://www.automationdirect.com/adc...n_(mechanical)

Is there any difference between the toque generated from a worm gear or from the belt and pulley?

Nope, torque is torque.

[disneytoy2]

Thanks Jim!

I knew I'd get good advice from you. So backlash is the main issue running from a worm gear via the center shaft, and I can avoid that with gearing like you mentioned. Unfortunately, I have had way too much time under a car changing starters, so I'm pretty familiar:-)

Plus, this will be very well balanced and all the weight right over the center.

[skrubol]

Anything using gearing will have backlash, unsurprisingly, automotive components only meant to transmit torque in one direction (like a starter) will have fairly high backlash. Not sure how well it could be adjusted out. The spline will have some backlash as well, but possibly could be mostly worked out by wrapping with teflon tape or something to get a fairly tight fit.

Any idea on how much backlash your application can tolerate? Will it have to be able to continoutly rotate 360+ degrees, or could it be made to only rotate back only across the same <360 degrees? Could do something like a linear belt drive common in 3d printers, but wrapped around the hub or table and fastened at the ends of the belt to the table. (would be hard to beat on price.)

[Jim Dawson]

Anything using gearing will have backlash, unsurprisingly, automotive components only meant to transmit torque in one direction (like a starter) will have fairly high backlash. Not sure how well it could be adjusted out.

The ring gear teeth are symmetrical, not sure about the starter gear. Put the motor on a pivot and springload the gears into a light over-mesh. Given the very low RPM & torque requirement it would work fine for this application. As an added bonus that method will take up any non-concentricity in the assembly.

[disneytoy2]

Jim, I'm going to go with your idea. I think one of the 168 tooth Flexplate is 14". That should be good because the main Z-column is 12x12" and I'd need room for the motor.

I will report back on my progress!!

I'm going with this one for $19.99 and I can pick it up in store tomorrow:-)

https://shop.advanceautoparts.com/p/...-111/5610346-p

[disneytoy2]

Hello Jim:-)

So, I was working with the Flex plate I got. 14" 164 teeth. If you take a look at the profile, I'm concerned the teeth are not really intended to be driven precisely.

What are your thoughts, can I get a motor gear to drive it without a lot of slop? I may return it and go a different way.

Thanks!!

[Jim Dawson]

If you are looking for +/- 0.001 degree accuracy then this would not be the proper drive system to use. But if you can live with 0.05 degree then it should work. Starter gears by their nature must be a bit loose in order to work properly. But, by over engaging the gears so the drive gear teeth engage to the bottom rather than having normal clearance you can minimize the backlash.

I mentioned above that I would mount the motor so the mount is on a pivot that would allow spring loading of the gear engagement. This of course would not work for the intended purpose of the ring gear/starter gear combo because the gears have to easily engage/disengage. But since in this application the gears would be continuously engaged, over meshing the gears will work fine. You just need to mount the starter gear on the motor shaft. The spring loading will also compensate for any runout in the ring gear, which I expect is not perfectly round.

[disneytoy2]

Okay, sounds good. I do remember you saying to spring load the motor at a slight angle. I was just concerned those teeth looked very deep and I was trying to picture how the motor gear would mesh inside.

I've worked on cars and know how the starter gear pops out and engages. Has to have some margin of error it it would never sync.

Thanks!

[Jim Dawson]

.....I do remember you saying to spring load the motor at a slight angle. ........

Not at an angle, but rather just allow the motor mount to swing on a pivot to adjust the mesh depth. However, setting the motor off perpendicular to the ring gear axis is an interesting idea, might actually work. Given the very slow speed and light loading you might get away with that.

[mactec54]

Hello Gang!

So I'm getting close to building the 28" round base for my Printer. This is a 2 meter tall clay printer. The base is 28" using a Ram 3500 Wheel Hub assembly. Very heavy duty. Now I need to give it rotation. I have 2 options.

1) Large pulley and belt. I don't need speed. and it will most likely never do more than 1 rotation. So major gear reduction.

Second, I thought about using the splined center hub. If I can find a cheap/used stub shaft, I'd need to adapt a smaller shaft that can key into a Worm Gear. I can drive this with either a nema 23 or 34 stepper.

Please see my diagram.

i like the elegance of using the intended shaft to rotate the machine.

I'm just not sure how much torque I need?

Is there any difference between the toque generated from a worm gear or from the belt and pulley?

Any suggestions appreciated!

Thanks

Randy

Torque a general term is the same, it's how it is used is what can be different, if your drive ratio is not low enough then you would need a higher torque motor to get the job done, 28" diameter when loaded is going to require a low ratio gearing, which I can't see you getting low enough with a belt drive, seeing you only want 1 or 2 rotations per minute then your worm drive would be best, start at around 60:1 or even a 100:1 for those small stepper motors, and for mounting the stepper motor a mounting plate and a timing belt pulley set up would then give you more opportunity to be able to change the ratio even more if you had to, either up or down and still use the same worm drive

[Black Forest]

Have you considered a belt on belt drive system? Look at Bell-Everman's rotary tables. It might give you some ideas.

[mactec54]

Hello Jim:-)

So, I was working with the Flex plate I got. 14" 164 teeth. If you take a look at the profile, I'm concerned the teeth are not really intended to be driven precisely.

What are your thoughts, can I get a motor gear to drive it without a lot of slop? I may return it and go a different way.

Thanks!!

The ratio is not going to be low enough for what you want to do, the Pinion gear also would have to much clearance on the sides of the teeth even if you put pressure on the pinion pushing it down into the teeth

If you have a very big high torque motor anything is possible

The industry standard for a rotary table is 40:1 and yours is much bigger than the norm so will nee a much higher ratio than the 40:1 for your little motors to drive it

[mactec54]

If you are looking for +/- 0.001 degree accuracy then this would not be the proper drive system to use. But if you can live with 0.05 degree then it should work. Starter gears by their nature must be a bit loose in order to work properly. But, by over engaging the gears so the drive gear teeth engage to the bottom rather than having normal clearance you can minimize the backlash.

I mentioned above that I would mount the motor so the mount is on a pivot that would allow spring loading of the gear engagement. This of course would not work for the intended purpose of the ring gear/starter gear combo because the gears have to easily engage/disengage. But since in this application the gears would be continuously engaged, over meshing the gears will work fine. You just need to mount the starter gear on the motor shaft. The spring loading will also compensate for any runout in the ring gear, which I expect is not perfectly round.

Even if the pinion was spring loaded / pushed in to the bottom of the teeth it will still have a lot of side clearance on the teeth

I think you mean +/- 1 degree these have no accuracy at all if you are talking about degrees of rotation

[disneytoy2]

Black Forrest, I will take a look at those. I don't have an issue with belt and pulley, Just It seemed like large pulleys were pretty expensive. And this is a very budget project:-)

mactec54, I do like the idea of a separate belt to the worm drive so I'm not locked into a final ratio. Until I get this moving a bit, I'm not 100% sure of the final RPM Min Max. I hope to get all the electrics wired up and see what looks right. I think my motor torque chart showed around 200 RPM as its sweet spot, So I'd need towork my way back from that.

Thanks to all for your advice.

I've solved a ton of little engineering problems. Often simplifying and removing weight and costly parts.:-)

[Jim Dawson]

The ratio is not going to be low enough for what you want to do, the Pinion gear also would have to much clearance on the sides of the teeth even if you put pressure on the pinion pushing it down into the teeth

If you have a very big high torque motor anything is possible

The industry standard for a rotary table is 40:1 and yours is much bigger than the norm so will nee a much higher ratio than the 40:1 for your little motors to drive it

Do you understand the end use of this system? ''Rotary table'' in this case is just a description of the function rather than a tool that machinists think of, this is actually more like a lazy susan, it is not for machine tool use. Rotational loading is almost zero and the RPM requirement is in the 1 to 2 RPM range. Extreme accuracy is not required either. Cost and weight are major considerations also. All of this taken together is the reason I suggested going this route.

[mactec54]

Do you understand the end use of this system? ''Rotary table'' in this case is just a description of the function rather than a tool that machinists think of, this is actually more like a lazy susan, it is not for machine tool use. Rotational loading is almost zero and the RPM requirement is in the 1 to 2 RPM range. Extreme accuracy is not required either. Cost and weight are major considerations also. All of this taken together is the reason I suggested going this route.

Yes a very large 3D printer by the first post, if he is printing anything it will have to be quite accurate at that diameter it will also have to have very little backlash also

[mactec54]

Black Forrest, I will take a look at those. I don't have an issue with belt and pulley, Just It seemed like large pulleys were pretty expensive. And this is a very budget project:-)

mactec54, I do like the idea of a separate belt to the worm drive so I'm not locked into a final ratio. Until I get this moving a bit, I'm not 100% sure of the final RPM Min Max. I hope to get all the electrics wired up and see what looks right. I think my motor torque chart showed around 200 RPM as its sweet spot, So I'd need towork my way back from that.

Thanks to all for your advice.

I've solved a ton of little engineering problems. Often simplifying and removing weight and costly parts.:-)

So if 200 RPM is where your best torque is then you would need 100:1 ratio to have the 2 RPM of the platform , so if you use the Ring gear you would only have approximately 32RPM at the motor for 2RPM of the platform

[disneytoy2]

Even though I don't anticipate 360 degree rotation. Like a record player I will need some speed to travel from point to point even though its angle is small. As the print head moves to the outer radius a small rotation will have a much larger effect in the Theta.

[mactec54]

Even though I don't anticipate 360 degree rotation. Like a record player I will need some speed to travel from point to point even though its angle is small. As the print head moves to the outer radius a small rotation will have a much larger effect in the Theta.

So having a low ratio gives you the best of both worlds, your motor can work in it's best power range for normal work, then can use higher RPM or lower if it is going to rotate back and forward, which most would be doing while printing, you would have to have near zero backlash at that diameter also, any Backlash at 28" diameter would be multiplied X the radius

So probably T5 or GT Timing Belts and pulleys would give you the best results, so to get a low ratio use a worm drive which you can adjust for almost zero backlash and use timing belts and pulleys to get what ever ratio you need to make your motor work

Now if you wanted to do something ridiculous, be creative, you could turn you 28" disc into a timing pulley and drive off the outside diameter you could use a T5 belt for this glued to the disc, or machine some timing pulley segments and fasten them to the disc, this could be under the top on a smaller daimeter