Printer lost position
For about a week now i have some problems with my printer (MK3S MMU2). It "forgets" it's position sometimes.
Problem is only occurring at the start of the print. If it gets past the first layer, the printer works flawless.
I did a factory reset, self test, XYZ-, and first layer calibration. Checked if the extruder doesn't bump into anything. All seems ok.
I'm testing Vesconite bushing at the moment (HiLube) and i did notice a lot of friction on the X-axis. I loosend the screws on the back of the extruder a bit and thing are ok-ish. Not as smooth as i expected them to be, but acceptable.
Just did a 16 hour print without problems. Want to start next print, crash ( see attached movie).
One problem that i'm having for a while now is i have to reset the printer after a print before i start the next print. If i don't do that, the printer just stops (without a message on the screen) before the first layer is done.
Any suggestions?
RE: Printer lost position
Your X belt is way too loose. You really need to tighten it up. Good time to check the Y belt, too. At least one notch tighter, maybe two.
-- ps: the belt numbers in the LCD display are motor torque readings; ignore them when tightening the belt.
While you are at it, triple check the belt drive gears are properly aligned to the motor shaft flats. If the gears are also spinning, the set screws were tightened in the wrong order: they must be tightened on the shaft flat first, then tightened on the shaft round. When loosening the set screws, loosen the shaft round screw first, then the shaft flat screw.
RE: Printer lost position
Your X belt is way too loose. You really need to tighten it up. Good time to check the Y belt, too. At least one notch tighter, maybe two.
-- ps: the belt numbers in the LCD display are motor torque readings; ignore them when tightening the belt.While you are at it, triple check the belt drive gears are properly aligned to the motor shaft flats. If the gears are also spinning, the set screws were tightened in the wrong order: they must be tightened on the shaft flat first, then tightened on the shaft round. When loosening the set screws, loosen the shaft round screw first, then the shaft flat screw.
I'm a bit confused about the right tension. At the time of the crash the X-belt tension was 200. I thought that was to tight as lower numbers means higher tension. I could feel the belt was not super tight so i have tighten the belt as you advised. Run a self test and belt tensions are:
Y: 277
X:220
So, are lower numbers tighter or looser? The X-belt feels like a guitarstring at the moment and i hesitate to test now with this kind of tension.
I forgot to mention in my previous post i have realigned the pully/gear on the steppermotor a bit yesterday, although nothing seemed to be out of the order.
Thanks.
RE: Printer lost position
The 220 means you have excessive friction on that axis, causing the motors to draw excess power to move. Belt tension affects the number maybe 5 points if you really over stretch the belt. 10 if you stretch the belt to the point it is bending the frame.
When building my printer, I had set my belts to over 30 pounds tension trying to get down to a 240 reading, I had to prybar the belts on to get even a small change: it was like 268 to 264. Later I learned the maximum rating for a 6 mm Gates GT2 is 25 lbf, and the motors are rated about 6 lbf max, and I loosened the belts.
When I replaced my first set of bearings, and actually greased them per the bearing manufacturer, my LCD numbers went to almost 300. I have been running my belts at 8 lbf (higher than I should), and my LCD usually reads 295 and 296 (my last reading was around 291 ... but my bearings are dry and need replacement). Each printer will vary, but the LCD numbers are not a reliable indicator of belt tension.
Belt tension needs to be measured. Pulling up on the middle of the lower belt with about 6.5 ounces force should deflect the X belt about 15/64". 6.5 ounces pull on the Y belt should deflect it about 12/64". These set the belt tension to about 6.6 lbf, and the belts will stretch down to 6 lbf ... about the max rating of the motor shaft bearings. I use a trigger pull spring scale, others use fishing or luggage scales that have low ranges.
And here's a little secret to dual set screw gears:
Flat First: Drive gears must be tightened flat-first.
1) Start with both set screws fully loosened so the pulley is free to spin on the motor shaft.
2) Align one set screw dead center with the flat on the motor shaft, slowly tighten the screw until it fully contacts the flat surface.
3) Torque the flat set screw to spec.
4) Now tighten the jam set screw, and torque it to spec.
Once tightened, never touch the flat set screw unless the jam screw is first fully loosened.
Why Flat First? Set screws have flat ends. If you tighten the jam screw first the set screw on the shaft flat doesn't fully contact the shaft, only one small edge of the screw surface is biting. Reversing torques can easily shift the shaft to a position the flat screw no longer contacts the shaft. This lets the jam screw wriggle loose. And after a while, vibration loosens the screws until the gear is free to rotate.
RE: Printer lost position
The 220 means you have excessive friction on that axis,....
I have replaced the X-axis Vesconite bushings with the stock bearings. The extruder is sliding much smoother now.
Run the usual tests; XYZ, first layer and self test.
Results of the self test:
X:268
Y:278
Much better now.
I have restarted the print and it didn't crash, whoohoo.
I will do some more prints before i tag this thread as "solved", but i think it was the friction of the bushings.
Thanks for your help Tim.
The trick with the dual set screw is something i already knew but probably very valuable for other people who read this thread.
Thanks again.