Z Axis Screw Cover

Hi,
I design an additional part for my Ormerod.
The Z Screw is quite anoying some time it almost get in to my eye during trying to do some adjustment on the ormerod
So I design a cover and also utilize it for holding a bearing to smooth the Z screw rotation and make it less swaying.
hope it useful somehow. BTW the Bearing I used is 695Z

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Chaisaeng
Hi,
I design an additional part for my Ormerod.
The Z Screw is quite anoying some time it almost get in to my eye during trying to do some adjustment on the ormerod
So I design a cover and also utilize it for holding a bearing to smooth the Z screw rotation and make it less swaying.
hope it useful somehow. BTW the Bearing I used is 695Z

It is not a good idea to hold the top of the Z lead screw captive so that it cannot move in circles, as you are then constraining it in 3 places instead of two and it cannot self-align. Doing so transfers the movement due to it not being perfectly straight to lateral forces on the Z nut and hence the X-axis arm, leading to ragged vertical edges on the print. Consider the case where the lead screw is significantly curved. If it is constrained only at the bottom and by the lifting nut, the top will twirl around in a circle but the rod will automatically center itself between the bottom and the lifting nut and still work reasonably. If the top is held captive however, the curve will act to make the nut try to describe circles instead of the top of the leadscrew, and force the X arm to move instead.

Therefore, if you want a cover as a safety shield for the top of the leadscrew, put it over the top of the threaded rod or give it a large hole that the rod can move freely inside (or use a thicker leadscrew that will stay perfectly straight). My suggestion would be to remove the bearing and allow the threaded rod to move inside the hole.

Dave
(#106)

Edited 1 time(s). Last edit at 05/04/2014 08:18AM by dmould.

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dmould

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Chaisaeng
Hi,
I design an additional part for my Ormerod.
The Z Screw is quite anoying some time it almost get in to my eye during trying to do some adjustment on the ormerod
So I design a cover and also utilize it for holding a bearing to smooth the Z screw rotation and make it less swaying.
hope it useful somehow. BTW the Bearing I used is 695Z

It is not a good idea to hold the top of the Z lead screw captive so that it cannot move in circles, as you are then constraining it in 3 places instead of two and it cannot self-align. Doing so transfers the movement due to it not being perfectly straight to lateral forces on the Z nut and hence the X-axis arm, leading to ragged vertical edges on the print. Consider the case where the lead screw is significantly curved. If it is constrained only at the bottom and by the lifting nut, the top will twirl around in a circle but the rod will automatically center itself between the bottom and the lifting nut and still work reasonably. If the top is held captive however, the curve will act to make the nut try to describe circles instead of the top of the leadscrew, and force the X arm to move instead.

Therefore, if you want a cover as a safety shield for the top of the leadscrew, put it over the top of the threaded rod or give it a large hole that the rod can move freely inside (or use a thicker leadscrew that will stay perfectly straight). My suggestion would be to remove the bearing and allow the threaded rod to move inside the hole.

Dave
(#106)

I wondered about that too Dave.

The top of my threaded rod moves in 10mm circle, and although I bought another rod it wasn't much better. It definitely makes the Z Nut creek on long Z moves, and there is significant blackening of the thread. (I have replaced the nut with a longer was as suggested in another thread)

I assume if you change the rod for something else you would need the same thread pitch or can this be altered by software/firmware?

Regards,

Les

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Pointy's Things
Pointy's Blog

Thanks for your suggestion. I'll test to print a square block to see whether it is ragged vertically.
If so i'll take the bearing out

There is also this one [www.thingiverse.com].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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Pointy
I wondered about that too Dave.

The top of my threaded rod moves in 10mm circle, and although I bought another rod it wasn't much better. It definitely makes the Z Nut creek on long Z moves, and there is significant blackening of the thread. (I have replaced the nut with a longer was as suggested in another thread)

I assume if you change the rod for something else you would need the same thread pitch or can this be altered by software/firmware?

Regards,

Les

You can have any pitch you like, just change the number of steps per mm in your config file (same command as used for the extruder, use Z instead of E). In my experience you will battle to get a thin threaded rod perfectly straight - if you need a straight leadscrew it should be a pretty beasty affair, but so long as the rod is constrained at only 2 places (the drive end and the leadscrew nut), a bit of flap won't do much harm. It's when you hold it at both ends that it becomes extremely important that it is straight.

In my experience dedicated leadscrews usually have a square cut thread. I suppose you could make up a custom leadscrew with a diameter of 10mm or more and modify the Ormerod accordingly, but I am not sure that it would make any significant difference to the quality of your prints.

Dave
(#106)

During the print before i have this screw cover, the thread rod sway more in the lower layer than the upper.
Not sure this is normal behavior of the thread rod supplied with the kit or not.
BTW. I just test print a simple cube and the quality of this test print is better than what i ever produced from my printer.
Any good explanation? Are there any bad effect if I left the bearing on the mount.

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Chaisaeng
During the print before i have this screw cover, the thread rod sway more in the lower layer than the upper.
Not sure this is normal behavior of the thread rod supplied with the kit or not.
BTW. I just test print a simple cube and the quality of this test print is better than what i ever produced from my printer.
Any good explanation? Are there any bad effect if I left the bearing on the mount.

Yes an unsecured rod end will normally sway more at the lower layers than upper layers because in effect the nut is acting like a fulcrum - the closer to the upper end it is, the smaller the movement at that end, and of course when the nut is at the very top the rod will not move at all because the nut will be acting just like your bearing. With the top held in a bearing the greatest forces trying to move the X axis will occur about half way up (assuming the rod is evenly curved) and the least forces at the bottom and top - so the worst effects will occur at a print height of about 100mm. If it has not degraded your print quality then stay with it, but it is not that change that was likely to have been responsible for the improvement you have seen.

Dave
(#106)