Heavy 15Kg bed + ball screws = problems with Z axis motor holding? I will have a very heavy (about 15 Kg) heated bed which will be raised and lowered via screws. I plan on using ball screws as I figure acme screws might wear quickly, also the friction would make it harder for the motor to raise and lastly ball screws would be more precise and accurate. I plan on using about a 3:1 ratio on the pulleys driving the screws which will help, but I am worried the motor ( a NEMA 23) may have trouble holding position with so much weight and low friction ball screws. I read on another thread someone recommending a motor with a brake. I guess like this one: Stepper with brake. Would that be a good idea? It would have the added advantage of stopping the bed slamming down in the event of a power failure. What would I have to do to configure my driver board (Duet WiFi) software for this type of motor? https://reprap.org/forum/read.php?4,797059,797059#msg-797059 Mon, 16 Mar 2026 18:00:59 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?4,797059,797660#msg-797660 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797660#msg-797660 forums.reprap.org]
There might be something there for you...]]> the_digital_dentist Reprappers Thu, 23 Nov 2017 08:00:19 -0500 https://reprap.org/forum/read.php?4,797059,797659#msg-797659 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797659#msg-797659 Thinking of trying a carbon fiber square tube for the x axis with a 9 or 12mm rail mounted on top.]]> SplatHammer Reprappers Thu, 23 Nov 2017 07:58:31 -0500 https://reprap.org/forum/read.php?4,797059,797658#msg-797658 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797658#msg-797658 SplatHammer Reprappers Thu, 23 Nov 2017 07:56:17 -0500 https://reprap.org/forum/read.php?4,797059,797231#msg-797231 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797231#msg-797231 MechaBits Reprappers Mon, 20 Nov 2017 16:08:49 -0500 https://reprap.org/forum/read.php?4,797059,797229#msg-797229 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797229#msg-797229
Quote
SplatHammer
A poster on another thread wrote as if the brake could be engaged by the software after lowering the bed a step. I was dubious so thanks for confirming my suspicions! : )

Sometimes a break will engage/disengage during regular operation but such cases are rare. The main situation where you will see this is when you want to lock the axis and then apply extreme forces that would overpower an unassisted servo.

An example would be CNC mill-turn or high speed indexed 4th/5th axes. The axis can be positioned at high speed, then locked in place to withstand cutting forces. (As an example, [ca-en.dmgmori.com] uses hydraulic clamps)

There is no point doing this for a 3d printer because there are no extra forces applied to a stopped axis. You could lock the Z axis for each layer - but the motor would be fine on its own so there is no benefit. As well, engaging and disengaging the brake will take some fraction of a second and might wiggle the shaft a few encoder counts, so it tends to degrade motion quality unless implemented very carefully.]]> 691175002 Reprappers Mon, 20 Nov 2017 15:58:50 -0500 https://reprap.org/forum/read.php?4,797059,797199#msg-797199 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797199#msg-797199 Thanks for that - I wasnt sure if the brake just came on after the bed had moved or if it was more for power loss. I am learning by reading posts
and unfortunately some people post without really understanding what they are talking about - a poster on another thread wrote as if the brake could be engaged by the software
after lowering the bed a step. I was dubious so thanks for confirming my suspicions! : )]]> SplatHammer Reprappers Mon, 20 Nov 2017 13:53:55 -0500 https://reprap.org/forum/read.php?4,797059,797198#msg-797198 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797198#msg-797198 Thanks, that does help! I am probably going to go with the ball screws, I worked out that with 16mm diameter screws with 4mm lead and 2 or 4 times advantage with pulley size I shouldnt have a problem
I think ball screws will be smoother and more accurate, plus I get a nice kit with thrust bearings and a mounting block for the ball nut. A 1604 ball screw means that you are only looking at 4mm for about 50mm
of thread (circumference) so its not putting much force on the motor (its like a wedge that goes 4mm higher for 50mm length), especially with mechanical advantage of the pulleys. I would play around with different options
but the time delay and DHL shipping costs (plus Spains €50 charge just for processing import tax) means I want to keep the number of packages to the minimum!]]> SplatHammer Reprappers Mon, 20 Nov 2017 13:50:40 -0500 https://reprap.org/forum/read.php?4,797059,797190#msg-797190 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797190#msg-797190
Brakes are used when the axis will back-drive without power. The brake is designed to close automatically when the machine loses power so that the axis doesn't fall to the bottom of its travel every time you turn the device off.

A brake will not improve performance while the printer is operating, and honestly should not even engage while the machine has power.]]> 691175002 Reprappers Mon, 20 Nov 2017 12:54:27 -0500 https://reprap.org/forum/read.php?4,797059,797128#msg-797128 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797128#msg-797128 deckingman Reprappers Mon, 20 Nov 2017 04:12:16 -0500 https://reprap.org/forum/read.php?4,797059,797123#msg-797123 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797123#msg-797123 SplatHammer Reprappers Mon, 20 Nov 2017 03:28:23 -0500 https://reprap.org/forum/read.php?4,797059,797075#msg-797075 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797075#msg-797075 deckingman Reprappers Sun, 19 Nov 2017 15:02:18 -0500 https://reprap.org/forum/read.php?4,797059,797074#msg-797074 Re: Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797074#msg-797074
The bed might lower to the bottom with a power failure, but I wouldn't expect it to slam down.]]> etfrench Reprappers Sun, 19 Nov 2017 14:59:29 -0500 https://reprap.org/forum/read.php?4,797059,797059#msg-797059 Heavy 15Kg bed + ball screws = problems with Z axis motor holding? https://reprap.org/forum/read.php?4,797059,797059#msg-797059 I plan on using ball screws as I figure acme screws might wear quickly, also the friction would make it
harder for the motor to raise and lastly ball screws would be more precise and accurate. I plan on using about a 3:1 ratio on the pulleys driving the screws which will help,
but I am worried the motor ( a NEMA 23) may have trouble holding position with so much weight and low friction ball screws. I read on another
thread someone recommending a motor with a brake. I guess like this one:
Stepper with brake.
Would that be a good idea? It would have the added advantage of stopping the bed slamming down in the event of a power failure.

What would I have to do to configure my driver board (Duet WiFi) software for this type of motor?]]> SplatHammer Reprappers Sun, 19 Nov 2017 13:13:08 -0500