Y Belt tension issue - very strange please help
As I have discovered that belt tension is key to print quality, and that they have to be tighter than you expect I have done the following.
Downloaded Y belt tension-er : http://www.thingiverse.com/thing:2786671
Downloaded X Belt tension-er : http://www.thingiverse.com/thing:2990861
I made a small mod to the X Belt adjuster as the hinge point snapped when inserting the screw, so thickened this up and made sure it cleared OK.
I also invested in new good quality re enforced belts Gates Powergrip® *2GT* Belt 6mm x 100mm. As I found even with adjuster the belts would stretch and would never get below 270-279.
So X Belt great at 249 now and happy with that.
But I have a real problem with the Y Belt . When I get the tension around 249 the carriage jams and auto home fails. Moving the carriage and can feel it binding. Loosed off the Y belt so its now at 273 and the binding goes away. Its like the tension distorts the geometry. How can this be as the specs say it should be in the 240-280 range ?
I have checked everything is nice and tight and no loose screws and and XYZ calibration is fine. Any suggestion greatly appreciated.
Re: Y Belt tension issue - very strange please help
Ignore the support menu belt status numbers.
They do NOT correlate well with belt looseness.
The printer cannot directly measure belt tension, it can only report motor rotation resistance. That is not the same as belt tension.
Loosen your belt tensions until pretty slack.
Take a 4-6 inch long rod and use the end of it to depress the middle of belt span. The rod's length gives you more sensitivity.
Notice how resistance changes as you gradually depress the belt. Initially, the change / amount of deflection is small. Then, as you begin to stretch the belt, the change increases faster.
Gradually increase belt tension until you feel that increase in required force happen at about 0.2 inches (5 mm) mid-span belt deflection. You don't need much more tension than that.
Observe the bottom half of each belt as your printer works. If the bottom portion is barely moving up/down as the carriages changes direction, you have enough tension. If you see it bouncing up and down a few mm, it's probably a bit too low tension.
Going too high distorts geometry, prematurely wears motor bearings, and causes extra motor heating.
Re: Y Belt tension issue - very strange please help
Thanks , that helps. So are we saying that the Belt status values are really irrelevant ?
Re: Y Belt tension issue - very strange please help
The belt status values seem to be more of a guide than an exact instrument... plus in my opinion very misleading as guy.k2 explained already.
I had a similar problem with my prints actually getting worse with higher belt tension (because I wanted them to get close to that 240 status value, too). Searched the web and found a good guide on youtube to calibrate the tension via the sound frequency (like a guitar string):
He is using a free tool that might not have the prettiest interface, but you can actually watch the frequency change as you tighten the belt and pluck it repeatedly. Only works if you have some kind of movable microphone of course.
For my Prusa Mk3 I ended up with X-Axis: 86Hz and Y-Axis: 76Hz (higher tone, because the belt is bit shorter).
Then after performing a selftest the printer showed the belt status values of X-Axis: 287 and Y-Axis: 295. So according to the official manual I'm outside the recommended range, but my prints are better and both axes move much more smoothly.
Hope that helps!
Re: Y Belt tension issue - very strange please help
Thanks , that helps. So are we saying that the Belt status values are really irrelevant ?
its not that they're irrelevant, its that they're not intended to be a scientific accurate measurement of "tension". 240 won't be the same for everyone, but if you get close to that its likely that you're in the ballpark at least.
240 is not "better" than 250, and if you're already sitting at 260 then you shouldn't stress about getting it lower.
it is entirely possible to stall out your motors with too much tension.