Initial calibration fails - The extruder movement is not smooth across the axis
 

Initial calibration fails - The extruder movement is not smooth across the axis  

  RSS
lee
 lee
(@lee-9)
New Member

Hi Folks

I have recently built my mk3s printer but it fails it calibration.

The extruder movement is not smooth across the X axis

The belt tension stats are y=260 and x=119   but I understand the these numbers are more relavent to the motor resistance rather than belt tension.  Belt tensions seems ok to me, both x and y have a nice twang to them.  Tried loosening the belt, lubing the rods and loosened the screws on the that hold the extruder to the axis, to no avail.

 

If it was a belt tension issue I'd expect the axis movement to be equally "sticky" across the lenght of the axis.  When moving the extruder it varies between slow (sticky) then smooth at the same points of the x axis drive motor rotation.  IE sticky for 3/4 of the drive motor rotation then smooth for the final 1/4 rotation.  Which repeats a number of times as the extruder is moved across the axis.  Could that indicate a motor issue?

 

Auto homing never finds the left hand side location, it usually sit just to the right.  If I auto home again the extruder dances and moves to the right again.

I have confirmed the pindar sensor works

When I run xyz calibration the extruder moves to the top of the z axis.  Asks to confirm the nozzle is clean then moves down and immediately fails.  There is no attempt to find home location once it moves down.

 

Any helpful suggestions out there ?

 

Many Thanks

Posted : 28/04/2020 6:00 pm
Agkirk
(@agkirk)
Trusted Member

I recently built a mk3S and experienced  a similar problem on the X axis.  I used a few drops of light synthetic oil (from my skateboarding sons days) on the rods and that seemed to fix the issue.  The stickiness  was not uniform across the rods, the top rod seemed to be the issue and several reports suggested the supplied grease might not get past the linear bearing end seals/wipers.  Likely a batch of bearings from Prusa that didn't get properly lubed.  I have used the unit for perhaps 70 hours with no problems.  I did oil again after 50 hours, just to be proactive.

Posted : 28/04/2020 7:40 pm
Peter M
(@peter-m)
Noble Member

Check if no cables or cable holders are hitting the x-axis, see backside and move x-axis to the end left and wright.

In the forum I read sometimes, loosening extruder, underneath are the bearings could help.

Bad bearings? put new grease in bearings, but you have to disassemble the rods.

Posted : 29/04/2020 11:31 am
lee
 lee
(@lee-9)
New Member

[video width="1280" height="720" mp4="https://forum.prusaprinters.org/wp-content/uploads/2020/04/X-Axis.mp4"][/video]

 

Oiled the rod to no avail

Added a video, where you can see the movement.   Does anyone elses move like that?

 

Posted : 29/04/2020 6:37 pm
lee
 lee
(@lee-9)
New Member
Ok,  have made some progress.   I unscrewed the grub screws that attach the x drive cog to the motor with a view to remove the cog gear and see it the stickyness persists.   But after undoing the grubs and wiggling the cog gear the sticky movement along the z axis disappeared.  So I can only assume that the gear was off center and causing the belt to rub on the motor bracket.
So with the stickyness gone, I attempted to auto home.  Success auto home works every time, where ever the extruder starts.
But, calibration stills in the exact same place.  Z axis moves to the top, check nozzle request.  Z axis moves straight down but does not  land on the home position and calibration fails.
 
Would appreciate any further suggetions
 
Many Thanks
Posted : 30/04/2020 3:29 pm
lee
 lee
(@lee-9)
New Member

All sorted now.   The hot end was mounted too low.  Corrected that, completed calibration and have done a test print

 

Thanks for your suggestions folks

Posted : 02/05/2020 6:50 pm
Share:

Please Login or Register