180-degree stepper lead screw coupling methods

[techvette]

I'm in the middle of a redesign, replacing some plywood sections with 1/2" aluminum and generally stiffening things up.

My previous design had the motors in line with the screws, using flexible shaft couplers. I've had issues with the couplers "stretching" leading to significant inaccuracy in the machine.

I'd like to mount the motors for my Y and Z axes next to the lead screws and drive them with a short belt, sort of like this:



I'm a little lost on where to source short belts - the stepper shaft and lead screws are only a few inches apart, though I have some flexibility here as I haven't yet mounted the motors.

My motors are dual-shaft NEMA23s with 1/4" shafts, using 8mm lead screws. I've found lengths of GT2 belt that are open-ended, but that won't work for this.

Suggestions?

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[ger21]

SDP-SI, or bbman.com

[louieatienza]

I'm in the middle of a redesign, replacing some plywood sections with 1/2" aluminum and generally stiffening things up.

My previous design had the motors in line with the screws, using flexible shaft couplers. I've had issues with the couplers "stretching" leading to significant inaccuracy in the machine.

I'd like to mount the motors for my Y and Z axes next to the lead screws and drive them with a short belt, sort of like this:



I'm a little lost on where to source short belts - the stepper shaft and lead screws are only a few inches apart, though I have some flexibility here as I haven't yet mounted the motors.

My motors are dual-shaft NEMA23s with 1/4" shafts, using 8mm lead screws. I've found lengths of GT2 belt that are open-ended, but that won't work for this.

Suggestions?

SDP/SI... But for couplers, either spider type (with zero backlash) or Oldham couplers would work better than the cheap helical couplers...

[wizard]

In many cases i prefer a belt drive so im with you in that regard.

Your first task is settling on a timing belt design or type. There are many types to choose from including the old trapzoidial, HTD, GT and others. Personally i like HTD.

Next you have to find a source. SDP has already been mentioned but is you live near a reasonably sized city there should be suppliers of bearings, belts and other motion control products. Kaman has branches all over the USA for example, but there are plenty of other vendors to choose from. So a quick look in your local area will likely turn up a supplier.

Then nationally there are all sorts of businesses that serve the online community. Simply looking for timing belts, bearings or motion control products will turn them up.

When searching on line it really helps to have a part number to search with. Manufacture web sites can help here as generally you want to buy stocked sizes.

Now all of that being said it should be pointed out that you can buy anti backlash couplings for inline mounting that work fine. To each his own but one reason to prefer belt drives is to reduce stick out. Depending upon the stepper, inline mounted motors just add too much to an axis. Use a belt drive and your stick out can approach zero.

[techvette]

Thanks, everyone, for the very helpful suggestions! This is exactly what I needed. I like the Oldham couplers for my X axis (center drive under the table), think I’ll do the belts for Y and Z.


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[techvette]

I got some decent belts and pulleys off of Amazon. Test fit looks good. Now I just have to figure out how to make a tensioner.

All of the tensioners I’ve seen online are for non-circulating belts, I think.


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[coherent]

I use this place for drive belts. Good price and selection.
Industrial Timing Belts & Pulleys Polytech Design Inc Clifton NJ 07011

I'm assuming your stepper mount screws are in slots so you can adjust belt tension? That should give you a little leeway regarding belt size.

[wizard]

I got some decent belts and pulleys off of Amazon. Test fit looks good. Now I just have to figure out how to make a tensioner.

All of the tensioners I’ve seen online are for non-circulating belts, I think.


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The easy way to do this is to bolt the motor through slotted holes.
The second easiest way is to bolt the motor mounting plate with slotted holes.

A idler/tensioner isnt bad either but it does involve more components. Some times you get better results with and idler/tensioner especially with longer belts and servos. In the old days anyways belt tension was critical for servo drives. Steppers should have less of a problem but you still beed proper tension. Another thing with idlers is that they can increase wrap significantly which can be useful if you are trying to implement a ratio.

[louieatienza]

The easy way to do this is to bolt the motor through slotted holes.
The second easiest way is to bolt the motor mounting plate with slotted holes.

A idler/tensioner isnt bad either but it does involve more components. Some times you get better results with and idler/tensioner especially with longer belts and servos. In the old days anyways belt tension was critical for servo drives. Steppers should have less of a problem but you still beed proper tension. Another thing with idlers is that they can increase wrap significantly which can be useful if you are trying to implement a ratio.

I'd tend to agree... an idler is really only needed when one pulley is very small compared to the other, over a short center distance, that there is not 180 degree tooth engagement on the smaller pulley. I've used the slot method on a stepper mount plate (which I believe in yet not many people use), and also on a plate with a pivot and curved slots at the other end - which happens to be a little easier to tension and lock with two hands.

[techvette]

I like the curved slot idea. Just have to figure out how to cut those in 1/2" Al.


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[wizard]

I like the curved slot idea. Just have to figure out how to cut those in 1/2" Al.


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A hand held router can cut those in aluminum, control your depth of cut and use jigs and fixtures to control movement. Of course be careful doing this. It most likely would be easier to set up to do slots for linear movements of the plates with hand tools though. Linear displacement mounts are also easier to guard.

Either method works but there are other considerations. For use with aluminum you will want to make up some thick washers to avoid crushing the slots. Thick washers help to reduce tightening damage and make fine adjustment easier. Second; it can be worthwhile to consider jack screws. As noted you sometimes want to have thre hands adjusting these, a jack screw can make life a lot easier. Third, make sure fir what ever belt series you use that you have clearance for a belt that is wide enough. Properly sized a belt drive will run for a very long time.

[elfrench]

I like Royal Supply for timing belts. They are less expensive compared to sd-spi.