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Z axis - screw opposite linear support?

Posted by rmlrn 
Z axis - screw opposite linear support?
February 25, 2016 09:00PM
I'm trying to figure out how to build my Z axis.

A common configuration seems to be a cantilevered bed supported by two linear rods with a drive screw in between:

R--S--R
|--------|
|--------|
---------

I'm wondering why this is used instead of having the screw support the opposite side of the platform, like this:

R-----R
|-------|
|-------|
---S---

What I'd actually thinking of doing is a single linear rail instead of two rods, with a leadscrew on the opposite side. Any drawbacks to this?

Edited 2 time(s). Last edit at 02/25/2016 09:02PM by rmlrn.
Re: Z axis - screw opposite linear support?
February 26, 2016 07:05AM
Ok after reading some more I think I understand - if the platform rotates perpendicular to the linear guide, then it will bind the screw.

So the screw "support" only works if the linear guide and platform are stiff enough not to need supporting.
Re: Z axis - screw opposite linear support?
February 26, 2016 07:49AM
Cantilevered beds can bounce/sag at the side opposite the guide rails/screw. I think adding a second screw to that opposite side would make the platform much more stable, provided the second screw is driven by the same motor as the first screw. If you use two motors, all bets are off - you're liable to create a new problem.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Z axis - screw opposite linear support?
March 11, 2016 01:13PM
If you're gonna use two screws and two rails, I suspect this is the ideal arrangement:

R------S
|---------|
|---------|
S------R

This allows for the maximum distance between elements, giving better leverage. Also, the bed's weight is evenly distributed.

Any disadvantages you can see?

Edited 1 time(s). Last edit at 03/11/2016 01:14PM by epicepee.
Re: Z axis - screw opposite linear support?
March 11, 2016 01:47PM
I wouldn't build it that way. I would put the guides closer to at least one of the screws to reduce the chances of it binding.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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