Another belt tension post  

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D Baker
(@d-baker)
New Member

The one thing making me crazy about my mk3s is the belt tension. Random loose pulley errors (always on x), error then 3 good passes then a couple of error notices and then ok with no changes made and pulley definitely tight.

Physical belt tension is inconsistent with readouts. My x axis will display 244 and my y axis 271, yet I can pluck the y belt and get a audible note in the 130 hz range and plucking the x provides a dull 60.  What's going on?

Posted : 11/11/2020 4:38 pm
karl-herbert
(@karl-herbert)
Illustrious Member
Posted by: @dennis-baker

The one thing making me crazy about my mk3s is the belt tension. Random loose pulley errors (always on x), error then 3 good passes then a couple of error notices and then ok with no changes made and pulley definitely tight.

Physical belt tension is inconsistent with readouts. My x axis will display 244 and my y axis 271, yet I can pluck the y belt and get a audible note in the 130 hz range and plucking the x provides a dull 60.  What's going on?

I secured the screws of the pulleys with medium strength Loctite. In principle you could also use lacquer. I always check the belt tension with my thumb and index finger method. With light pressure it should not be possible to compress the belt so far that the inner sides touch each other. I don't pay attention to the Prusa LCD display, because too many factors can influence the values (stiff linear bearings).
But this is only one of many possibilities - many roads lead to Rome.

 
Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 11/11/2020 5:15 pm
--
 --
(@-2)
Illustrious Member
@dennis-baker

The drive gear set screws must be fastened in order: FLAT FIRST. If you don't do this, you will need locktite to hold the screws in place, but the gear will still loosen on the shaft.

  1. Loosen both set screws so the gear is free to spin.
  2. Align and tighten the set screw to the flat of the motor shaft. 
  3. Tighten the jamming set screw - the one on the shaft round.

You are done.  To remove the gear, loosen the jam set screw first, then the flat set screw.

To measure belt tension you must use the deflection method. The firmware menu is - well - a waste of time.

  1. Power off the printer.
  2. Push the extruder far left, the bed far rear.
  3. Apply about 7 ounces; 200 grams force to the lower belt of the pairs (longest free length).
  4. Measure the belt deflection:
  5. X should be about 15/64s; 6mm
  6. Y should be about 12/64s; 5mm. 

This provides about 6 lbf tension in the belts.
 -- The Gates 6 mm belt is spec'd 2 to 25 lbf.
 -- The stepper motors are spec'd for a maximum of 8 or 11 lbf radial load - depending on who made them.

 

This post was modified 5 months ago by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 12/11/2020 12:24 am
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