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Backlash Nuts, face up or down

Posted by Dunston-UK 
Backlash Nuts, face up or down
October 17, 2019 07:42AM
Hi

Which way is the correct way or the best way to mount the backlash nuts on a CoreXY, some say when facing down the bed is quasi resting on the spring. Does it not matter? as long as the two parts are placing the spring under enough tension that it's force is arresting the over/under turning of the lead screw?
Re: Backlash Nuts, face up or down
October 17, 2019 10:48AM
It don't think it matters which way you put the nuts, but...

When you're moving a load horizontally with a screw, when the screw reverses direction you can get backlash because there is a gap between the screw and nut threads. An antibacklash nut uses a spring to keep the threads engaged in both directions by pushing two nuts against the screw threads (which increases friction).

When you're lifting a load against gravity, no matter which way the screw turns, gravity is pulling down on the load and keeping the screw and nut threads engaged. As long as the mechanism drops freely under gravity (without the screws connected), there's no need for antibacklash nuts on a vertical screw drive. If the mechanism doesn't drop freely under gravity, the guide rails may be out of alignment and that should be corrected.

Edited 2 time(s). Last edit at 10/17/2019 10:52AM by the_digital_dentist.


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Re: Backlash Nuts, face up or down
October 17, 2019 10:57AM
Quote
the_digital_dentist
It don't think it matters which way you put the nuts, but...

When you're moving a load horizontally with a screw, when the screw reverses direction you can get backlash because there is a gap between the screw and nut threads. An antibacklash nut uses a spring to keep the threads engaged in both directions by pushing two nuts against the screw threads (which increases friction).

When you're lifting a load against gravity, no matter which way the screw turns, gravity is pulling down on the load and keeping the screw and nut threads engaged. As long as the mechanism drops freely under gravity (without the screws connected), there's no need for antibacklash nuts on a vertical screw drive. If the mechanism doesn't drop freely under gravity, the guide rails may be out of alignment and that should be corrected.

The Bed drops freely when the Nema17s are not energised so the rods are in alignment, I fully understood what and how the backlash nuts work, plenty of online information about it all, but I was unable to find out a definitive, this way up or that way down rotation.
Re: Backlash Nuts, face up or down
October 18, 2019 02:57AM
I would expect the main nut to be produced with higher precision than the backlush nut, so I would place the main nut near the bed.
Re: Backlash Nuts, face up or down
October 18, 2019 03:29AM
-It makes sense to have the "main" nut (that is fixed to the frame) support the weight of the bed (Note, nuts precision is the same, made with the same tooling !!!!! Statement above irrelevant).

-If the set up is OK meaning there is no binding, the antibacklash mechanism won't be used.

Therefore it doesn't make sense to use an antibacklash nut here.

Edited 2 time(s). Last edit at 10/18/2019 09:19AM by MKSA.


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Re: Backlash Nuts, face up or down
October 18, 2019 04:45PM
Quote
MKSA
Note, nuts precision is the same, made with the same tooling !!!!! Statement above irrelevant).

Thank you for sharing your knowledge about the production process.

I would have expected high precision from the nut and expected little friction and low precision from the antibacklash nut, because with the antibacklash nut it is not precision but low friction that is important.

Edited 2 time(s). Last edit at 10/18/2019 05:05PM by JoergS5.
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