[Solved] Layershifts in direction of travel  

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mickebarnes
(@mickebarnes)
Active Member

[PRUSA i3 Mk3S (v3.9.1-3518) | Layer Shifts in direction of travel]
√ Calibration(BeltStatus) X:256, Y:268
√ Pulley's @Steppers have been checked tight and aligned (belt rides in center of toothed section).
√ Axis bearing rods have been checked/aligned, lubricated.
√ Initial/new calibration performed/ all self checks passed.

[SYMPTOMS]
1) Multiple layer shifts observed -only when/if printhead travels during print.
2) Not observed on simple or single object prints with little or no travel during print job.

Any advice/insights?
I've read the documentation on layershifts. My belt tensions are w/in spec and pulley's are secured.
I'd like to increase 'Z-Hop' on travel but can't find that setting in the PrusaSlicer.

--thank you

[IMAGES]

Posted : 23/10/2020 11:55 pm
mickebarnes
(@mickebarnes)
Active Member

I just found "Z-Hop" as "Lift Z" under [Printer Settings].

I've changed it from the default .6mm to 1.00mm and am running a test print now.

Posted : 24/10/2020 12:37 am
mickebarnes
(@mickebarnes)
Active Member

Simple test print completed successfully w/ 1.00mm Lift-Z change. 
I'll start a complex/production print and report/close/expand this post when complete.

Posted : 24/10/2020 2:10 am
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 -2
(@-2)
Illustrious Member

Belt status is meaningless for belt tension. It shows axis friction. So if a number is lower than 300 you have sticky bearings.

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 24/10/2020 3:57 am
mickebarnes
(@mickebarnes)
Active Member

[FINAL] 
Production prints are coming out well and without layershifts.  -these are fairly complex prints with overhangs and multiple object/parts on all areas of the print bed (Ikea Lack enclosure pieces).  I'm satisfied w/ the results. --closing.

Posted : 25/10/2020 12:57 am
mickebarnes
(@mickebarnes)
Active Member

@tim-m30

I can see how  'belt tension' and 'axis friction' are different phenomenon.  How would you quantify each?  How would you resolve each as a separate issue? 

Posted : 25/10/2020 1:01 am
--
 -2
(@-2)
Illustrious Member

Belt tension is the force within a belt, or roughly, how much the belt is being stretched.  Gates specs GT3 at 2 to 25 lbf for a 1/4: section. The stepper motors have a maximum radial shaft force around 8 to 11 lbf.  I set my belts to around 6 lbf tension.

Friction is the force required to move an axis. Stiction being the force required to start movement, friction the force to maintain it.

The readout "belt tension" is a crude measurement of axis friction based on motor drive currents available to the TMC motor controllers. This number has zero to do with belt tension, unless there is no other friction in the system, which, there always is. 

I think somewhere early in development someone had the bright idea that you could measure belt tension as a factor of bearing friction.  That is, the friction in the one roller bearing in the idler pulley the belt rides through. Unfortunately, the rubber seals on the linear bearings alone swamps that friction. And when you add all the places extra unwanted friction is added (ungreased bearings, crimped bearings are two biggies)... well, the friction the belts add to the drive system currents is unmeasurable.

This post was modified 1 month ago by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 25/10/2020 3:40 am
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