Driving Two Leadscrews With One Stepper Using a Belt This design has the two leadscrews driven by one stepper to eliminate the problems that can occur with driving two z leadscrews each with their own steppers. The leadscrews hang from the top of the printer. Inside the cylindrical housing is a thrust bearing supporting the leadscrew. Radial bearings position the leadscrew left and right [but see point 3 below]. The bottom end of the leadscrews sits in a protector bracket but is free moving. I have some concerns: 1) Can the single stepper support the x cross member when it's powered off? Or will the weight of the assembly pull down enough to turn the stepper? (The leadscrew is Tr8*8) 2) Could there be enough play between the belt teeth and the GT2 pulley so that z movements will not be precise enough? 3) Will it be difficult to position the leadscrew centered axially over the leadscrew nut? My concern is the leadscrew isn’t a tight fit inside the two radial bearings (one inside the lower cylindrical housing and one in the upper hosuing) and there might be the tiniest bit of slop. When the belt is tensioned the leadscrew will be pulled tight against the inside of the bearing. The leadscrew nut mounted to the x cross member can move left and right to adjust it's position under the center of the leadscrew along x, BUT it cannot move front and back (y) at all because the leadscrew nut housing is a fixed size. When the belt is tensioned in the way I have drawn it here there will be some rearward pull (y) on the leadscrew. This could pull the leadscrew out of axial alignment with the leadscrew? Two idler pulleys could be added to the belt path so it would only pull directly to the center of the machine, thus eliminating that problem but I'm wondering if that is even needed? I'd appreciate comments if this is a good arrangement or should I consider another? Thank you. [Sorry the belt isn’t drawn properly around the stepper pulley.] [attachment 85384 leadscrews.png] https://reprap.org/forum/read.php?14,717302,717302#msg-717302 Sat, 11 Jul 2026 01:11:20 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?14,717302,721286#msg-721286 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,721286#msg-721286
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the_digital_dentist
Draw the thing in CAD, measure the lengths of the straight belt segments, add to that the lengths wrapped around the pulleys. That will get you into the ball-park. Then make the motor or pulleys adjustable to adjust tension. Make sure you pick a belt that's a little longer than you need- you can always take up slack, but there isn't much you can do if the belt is too short.

That's what I had thought to do as well. Old school would be to wrap string around the pulleys and measure? That might be easy and quite accurate? Drawing/calculating should be bang on too I suppose.]]> Garry Bartsch Mechanics Mon, 07 Nov 2016 18:13:42 -0500 https://reprap.org/forum/read.php?14,717302,721283#msg-721283 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,721283#msg-721283
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Origamib
I have a similar system rigged up to mine. The stepper can easily be moved left and right to make it tighter, as well as the two central pulleys. This means the belt can be any length (within reason) and then just move the stepper to take up the slack.

Cool setup. How's the print quality from this machine? Do you have any pictures of the entire machine?]]> Garry Bartsch Mechanics Mon, 07 Nov 2016 18:10:20 -0500 https://reprap.org/forum/read.php?14,717302,721277#msg-721277 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,721277#msg-721277 the_digital_dentist Mechanics Mon, 07 Nov 2016 17:45:36 -0500 https://reprap.org/forum/read.php?14,717302,721249#msg-721249 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,721249#msg-721249

]]> Origamib Mechanics Mon, 07 Nov 2016 16:08:18 -0500 https://reprap.org/forum/read.php?14,717302,721186#msg-721186 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,721186#msg-721186
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dthomas6184
How did you go about picking your belt length? i'm looking to implement a similar 2 screw 1 motor setup myself to drive my bed instead of a cantilever bed setup.

I haven't gotten to that point yet so it's a bridge I'll have to work on crossing eventually.]]> Garry Bartsch Mechanics Mon, 07 Nov 2016 12:36:03 -0500 https://reprap.org/forum/read.php?14,717302,721183#msg-721183 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,721183#msg-721183 dthomas6184 Mechanics Mon, 07 Nov 2016 12:31:55 -0500 https://reprap.org/forum/read.php?14,717302,718659#msg-718659 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718659#msg-718659
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the_digital_dentist
If they are properly heat sunk (soldered to a large ground plane in a PCB), they can deliver more current than it they are not properly heat sunk (plug-in modules).

Great explanation. I have a feeling I will need to review the electronic section of your SoM Instructable. It seems maybe you are hinting there is more information about this there.]]> Garry Bartsch Mechanics Mon, 31 Oct 2016 12:31:30 -0400 https://reprap.org/forum/read.php?14,717302,718630#msg-718630 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718630#msg-718630
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Garry Bartsch

I'm remembering (maybe): amps are pulled not pushed? Drawing too much current from the driver will fry it? From the above it sounds like I can use a NEMA-17 anyway without overworking it.

The drivers act as current sources and will modulate the waveform sent to the motor to achieve the rms current you have set the chip to deliver. The driver chips are not 100% efficient, so setting current too high will cook them. If they are properly heat sunk (soldered to a large ground plane in a PCB ), they can deliver more current than if they are not properly heat sunk (plug-in modules). Gluing a tiny heat sink to the top of a plastic chip is not proper heat sinking. The data sheet for the driver chip has a maximum operating current rating based on proper heat sinking. You can't operate at that maximum current if you don't get rid of the heat.]]> the_digital_dentist Mechanics Mon, 31 Oct 2016 10:37:06 -0400 https://reprap.org/forum/read.php?14,717302,718485#msg-718485 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718485#msg-718485
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the_digital_dentist
I used a 5mm pitch XL belt because I had the 42 tooth pulleys for the screws and the 20 tooth pulley for the motor. In my machine, the X axis weighed about 4-5 kg. I would not have felt comfortable with 6 mm GT2 belt. Maybe 9 or 10 mm would be OK.

My x axis weighs very close to 1.5 kg. so I'm guessing finding a NEMA-17 that can lift this will be easy even if I use a 20 tooth pulley on the z screws and the motor. But a 40 tooth on the screws would be really safe.

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the_digital_dentist
I drove NEMA-23 motors with a RAMPS board for a long time. As long as you keep the current within the driver's capabilities you can drive any size motor. The NEMA-23 motors I used were not especially high torque for that size motor and were rated at 2A. I used a small one that delivered about 100 oz-in holding torque which can be done with a NEMA-17 motor, and a couple 130-150 oz-in motors.

I'm remembering (maybe): amps are pulled not pushed? Drawing too much current from the driver will fry it? From the above it sounds like I can use a NEMA-17 anyway without overworking it.]]> Garry Bartsch Mechanics Sun, 30 Oct 2016 21:43:34 -0400 https://reprap.org/forum/read.php?14,717302,718472#msg-718472 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718472#msg-718472
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the_digital_dentist
I think the main problem with over tightening belts is that it can cause the motor or other pulleys to tilt if they aren't mounted very solidly (one of the problems with non metallic printer frames) resulting in the belt teeth engaging the pulley's teeth at an angle. That will wear the belt quickly.

My friend who supports the end of the stepper shaft broke a shaft because the belt was too tight. Sounds crazy and he was surprised. But now that he supports them he doesn't have trouble with wear likely for the reason you mention: the shaft isn’t tilted at all.]]> Garry Bartsch Mechanics Sun, 30 Oct 2016 19:26:36 -0400 https://reprap.org/forum/read.php?14,717302,718471#msg-718471 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718471#msg-718471 the_digital_dentist Mechanics Sun, 30 Oct 2016 19:16:13 -0400 https://reprap.org/forum/read.php?14,717302,718467#msg-718467 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718467#msg-718467
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JamesK
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My x and y steppers have the ends supported

Out of interest, how did you arrange that? The shaft on my motors isn't long enough to pass through the pulley and into a bearing.

Indeed the shafts are barely long enough. For y I printed a block that holds a bearing. The stepper shaft doesn't protrude through the bearing enough shaft is in the bearing to support it. Both ends of x are similarly supported in a block (the idler end has a toothed pulley with two bearings).

[attachment 85587 2016-10-30_16h15_28.png]]]> Garry Bartsch Mechanics Sun, 30 Oct 2016 18:59:47 -0400 https://reprap.org/forum/read.php?14,717302,718466#msg-718466 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718466#msg-718466
I drove NEMA-23 motors with a RAMPS board for a long time. As long as you keep the current within the driver's capabilities you can drive any size motor. The NEMA-23 motors I used were not especially high torque for that size motor and were rated at 2A. I used a small one that delivered about 100 oz-in holding torque which can be done with a NEMA-17 motor, and a couple 130-150 oz-in motors.]]> the_digital_dentist Mechanics Sun, 30 Oct 2016 18:57:54 -0400 https://reprap.org/forum/read.php?14,717302,718458#msg-718458 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718458#msg-718458
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My x and y steppers have the ends supported

Out of interest, how did you arrange that? The shaft on my motors isn't long enough to pass through the pulley and into a bearing.]]> JamesK Mechanics Sun, 30 Oct 2016 17:55:00 -0400 https://reprap.org/forum/read.php?14,717302,718455#msg-718455 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718455#msg-718455
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JamesK
Yes again to 6mm GT2 belt. I think it's adequate for the job, but the relatively shallow profile does seem more prone to jumping a tooth than the chunkier belts I've seen. I don't think you will have any problems with the belt path you now have, and given that your frame looks plenty rigid enough to carry adequate belt tension.

My x and y steppers have the ends supported so those belts can be snugged right up (I guess tighter is better for consistent nozzle positioning) and they should not slip because of their almost full wrap on the pulley. I could do something similar for the z arrangement but likely won't because of DD's advice before about belt wear. However, I do have a friend who run his belts really tight and he said he isn’t wearing them out. Maybe there are different grades of belts?

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JamesK
We'd all like to have layer registration like DD's! Mine can't match that, I think because of the overly flexible (whippy!) 8mm smooth rods in it. The next build will hopefully be a lot more rigid using linear guides.

That's my goal. If I don't achieve it I won't be happy. With linear guides on z there is no play so as long as the layers are a consistent height, and x and y move the same distance repeatedly, the edges should be perfect. My first printer was a commercial UP! Plus using linear rails and surface finish was gorgeous so I knew I wanted to make one with linear rails.]]> Garry Bartsch Mechanics Sun, 30 Oct 2016 17:46:00 -0400 https://reprap.org/forum/read.php?14,717302,718445#msg-718445 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718445#msg-718445
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But if I did as you with larger pulleys on the screws then the smaller stepper would be fine? I'm just learning as I go and relying heavily on experience like yours and others. Your belts are 6mm GT2?

Yes, if you use larger pulleys on the screws and a smaller one on the motor you get a gearing advantage that reduces the load on the motor. So with a 20T pulley on the motor and 40T on the screws I get a 2:1 reduction that lets the nema17 cope much better than it did before. I have a relatively heavy X axis with a dual direct extruder setup, so my guess is that a nema17 will cope for your design too. The other place you can get some mechanical advantage is to use a smaller lead on the screw. I've been thinking of getting some T12 with 2mm lead.

Yes again to 6mm GT2 belt. I think it's adequate for the job, but the relatively shallow profile does seem more prone to jumping a tooth than the chunkier belts I've seen. I don't think you will have any problems with the belt path you now have, and given that your frame looks plenty rigid enough to carry adequate belt tension.

We'd all like to have layer registration like DD's! Mine can't match that, I think because of the overly flexible (whippy!) 8mm smooth rods in it. The next build will hopefully be a lot more rigid using linear guides.]]> JamesK Mechanics Sun, 30 Oct 2016 16:53:16 -0400 https://reprap.org/forum/read.php?14,717302,718438#msg-718438 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718438#msg-718438
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the_digital_dentist


Great pictures. I can see nicely how you did many things. I WANT layer alignment like you. That is just killer.

Your machine has a heavy belt for Z. Can I expect not to have trouble using 6mm GT2? Or is a heavy belt required?


]]> Garry Bartsch Mechanics Sun, 30 Oct 2016 16:14:56 -0400 https://reprap.org/forum/read.php?14,717302,718437#msg-718437 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718437#msg-718437
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JamesK
Looks good. What size motor are you using for Z?

This machine is in the design stage so I haven't settled on a stepper but I'm wondering if I should be considering a NEMA-23? Can NEMA-23 run off the same driver as a NEMA-17? But if I did as you with larger pulleys on the screws then the smaller stepper would be fine? I'm just learning as I go and relying heavily on experience like yours and others. Your belts are 6mm GT2? (Please see my question to Mark about belts.)]]> Garry Bartsch Mechanics Sun, 30 Oct 2016 16:12:01 -0400 https://reprap.org/forum/read.php?14,717302,718329#msg-718329 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718329#msg-718329
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Garry Bartsch
[attachment 85429 beltpath.png]

This is how I had thought to route the belt so it would pull inwards only. Plus it would give the belt contact with the stepper pulley as Mark advised.

That's almost exactly how I did it in my first printer and it worked perfectly. I put the motor off to one side so I could feed filament from the central part of the frame.
You can see the pulleys and just a little of the motor to the right of the filament spools. I used 42 tooth pulleys on the screws and a 20 tooth pulley on the motor. The screws were (and still are) 4 starts, 1/2" lead.



No Z artifacts at all in spite of dire warnings about using imperial screws:



I used a NEMA-23 motor (I don't recall the torque spec) because I had one handy. My X axis was very heavy and I doubt a NEMA-17 motor would have been able to lift it.
]]> the_digital_dentist Mechanics Sun, 30 Oct 2016 08:19:44 -0400 https://reprap.org/forum/read.php?14,717302,718321#msg-718321 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,718321#msg-718321 JamesK Mechanics Sun, 30 Oct 2016 07:45:09 -0400 https://reprap.org/forum/read.php?14,717302,717602#msg-717602 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717602#msg-717602 the_digital_dentist Mechanics Thu, 27 Oct 2016 00:36:17 -0400 https://reprap.org/forum/read.php?14,717302,717597#msg-717597 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717597#msg-717597
This is how I had thought to route the belt so it would pull inwards only. Plus it would give the belt contact with the stepper pulley as Mark advised.]]> Garry Bartsch Mechanics Wed, 26 Oct 2016 22:44:59 -0400 https://reprap.org/forum/read.php?14,717302,717589#msg-717589 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717589#msg-717589
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the_digital_dentist
No, not nearly that tight. If you make the belts too tight they wear faster. In the Z axis, it probably won't wear much at all, anyway, but you don't want the tension causing unnecessary loading on the motor, either.

The belt should be just tight enough... ;)

I like it ... just tight enough.

On the advice of a friend I have supported the ends of the y and x stepper shafts. This way the y and x belts can be fairly tight without putting stress on the stepper bearing or the shaft. But I'll be careful not to over tighten them because of the wear issue.]]> Garry Bartsch Mechanics Wed, 26 Oct 2016 20:54:55 -0400 https://reprap.org/forum/read.php?14,717302,717583#msg-717583 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717583#msg-717583
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o_lampe
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DD
You will wonder, as I do, why anyone messes around with dual motor arrangements

Maybe because you'd need a rigid printer frame to cope with the belt tension. Something I wouldn't dare to try with my cheap acrylic framed Prusa I3...

I wonder about acrylic frames, too.]]> the_digital_dentist Mechanics Wed, 26 Oct 2016 20:19:26 -0400 https://reprap.org/forum/read.php?14,717302,717582#msg-717582 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717582#msg-717582
The belt should be just tight enough... ;)]]> the_digital_dentist Mechanics Wed, 26 Oct 2016 20:18:30 -0400 https://reprap.org/forum/read.php?14,717302,717544#msg-717544 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717544#msg-717544 Garry Bartsch Mechanics Wed, 26 Oct 2016 15:23:40 -0400 https://reprap.org/forum/read.php?14,717302,717483#msg-717483 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717483#msg-717483
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DD
You will wonder, as I do, why anyone messes around with dual motor arrangements

Maybe because you'd need a rigid printer frame to cope with the belt tension. Something I wouldn't dare to try with my cheap acrylic framed Prusa I3...]]> o_lampe Mechanics Wed, 26 Oct 2016 12:08:35 -0400 https://reprap.org/forum/read.php?14,717302,717310#msg-717310 Re: Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717310#msg-717310
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Garry Bartsch
This design has the two leadscrews driven by one stepper to eliminate the problems that can occur with driving two z leadscrews each with their own steppers. The leadscrews hang from the top of the printer. Inside the cylindrical housing is a thrust bearing supporting the leadscrew. Radial bearings position the leadscrew left and right [but see point 3 below]. The bottom end of the leadscrews sits in a protector bracket but is free moving.

I have some concerns:

1) Can the single stepper support the x cross member when it's powered off? Or will the weight of the assembly pull down enough to turn the stepper? (The leadscrew is Tr8*8)

It is unlikely that the weight of the X axis will turn the motor, allowing the X axis to drop, but if you used larger pulleys on the screws than on the motor you'd get increased resolution (not that you need it) and the X axis would be less likely to drop.

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Garry Bartsch

2) Could there be enough play between the belt teeth and the GT2 pulley so that z movements will not be precise enough?
Compared to what, two motors driving two screws that get out of sync every time you look at them? It will work fine.

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Garry Bartsch
3) Will it be difficult to position the leadscrew centered axially over the leadscrew nut? My concern is the leadscrew isn’t a tight fit inside the two radial bearings (one inside the lower cylindrical housing and one in the upper hosuing) and there might be the tiniest bit of slop. When the belt is tensioned the leadscrew will be pulled tight against the inside of the bearing. The leadscrew nut mounted to the x cross member can move left and right to adjust it's position under the center of the leadscrew along x, BUT it cannot move front and back (y) at all because the leadscrew nut housing is a fixed size. When the belt is tensioned in the way I have drawn it here there will be some rearward pull (y) on the leadscrew. This could pull the leadscrew out of axial alignment with the leadscrew?

Two idler pulleys could be added to the belt path so it would only pull directly to the center of the machine, thus eliminating that problem but I'm wondering if that is even needed?

I'd appreciate comments if this is a good arrangement or should I consider another? Thank you

The bearings should fit tightly. If they don't, get the right size bearings or turn the screws down to fit properly. If there are bearings anchored to the frame rear-ward forces due to belt tension shouldn't matter any more that the forces pulling toward the motor. You definitely don't have enough teeth on the motor bearing engaging the belt. You'll need a couple pulleys to wrap more belt around the motor pulley. I read on one of the belt manufacturer's web sites that belts should engage 6 teeth or 90 degrees, whichever is greater.

Here's the way I arranged things in my printer:




Once you have the mechanism put together, you will discover that besides keeping the X axis in permanent alignment, it will be MUCH easier to work on the extruder or X axis with the single motor. You won't have to turn on the printer and computer, then step through multiple menus to jog the Z axis. All you have to do is pull the belt whether the power is on or off. Leveling and zeroing the bed becomes fast and trivially easy. You will wonder, as I do, why anyone messes around with dual motor arrangements.
]]> the_digital_dentist Mechanics Wed, 26 Oct 2016 00:15:47 -0400 https://reprap.org/forum/read.php?14,717302,717302#msg-717302 Driving Two Leadscrews With One Stepper Using a Belt https://reprap.org/forum/read.php?14,717302,717302#msg-717302
I have some concerns:

1) Can the single stepper support the x cross member when it's powered off? Or will the weight of the assembly pull down enough to turn the stepper? (The leadscrew is Tr8*8)

2) Could there be enough play between the belt teeth and the GT2 pulley so that z movements will not be precise enough?

3) Will it be difficult to position the leadscrew centered axially over the leadscrew nut? My concern is the leadscrew isn’t a tight fit inside the two radial bearings (one inside the lower cylindrical housing and one in the upper hosuing) and there might be the tiniest bit of slop. When the belt is tensioned the leadscrew will be pulled tight against the inside of the bearing. The leadscrew nut mounted to the x cross member can move left and right to adjust it's position under the center of the leadscrew along x, BUT it cannot move front and back (y) at all because the leadscrew nut housing is a fixed size. When the belt is tensioned in the way I have drawn it here there will be some rearward pull (y) on the leadscrew. This could pull the leadscrew out of axial alignment with the leadscrew?

Two idler pulleys could be added to the belt path so it would only pull directly to the center of the machine, thus eliminating that problem but I'm wondering if that is even needed?

I'd appreciate comments if this is a good arrangement or should I consider another? Thank you.

[Sorry the belt isn’t drawn properly around the stepper pulley.]

[attachment 85384 leadscrews.png]]]> Garry Bartsch Mechanics Tue, 25 Oct 2016 23:13:26 -0400