Belts constantly slipping: correct tension?

The belts on my prusa i3 seem to consistently slip (not sure whether they slip because of binding of the carriages or something else, but I can sometimes hear the loud grinding noise of what I'm guess is teeth slipping on the pulley when it happens). It was happening more for the x axis than for y. As a fix, I tried adding some homemade tensioners to both the x and y axis, as both felt rather slack despite my efforts to tighten at the carriage connection points. Now the x axis does not seem to slip, but the y is slipping more instead... When I loosened the tension, it seems to have started slipping by smaller amounts. Still slips though, even though the y axis belt now feels considerably more slack than the x axis one (which no longer seems to slip).

ll probably remove the y tensioner entirely to see if it helps, but I wanted to hear a professional opinion on what the correct tension should be on the belts. It was my understanding that overtension can cause binding of carriage/bearings and hence slipping of the belt, while undertension tends to cause backlash. Is there some good way to tell when the tension is just right? I'm getting tired of restarting print after print and have no idea how long it'll take me to find the "perfect" tension by trial and error.

For example, is slipping always evidence of a belt that's too tight? Or can it slip both if too tight and too loose. If I loosen it too much, will backlash immediately manifest itself in the form of skewed shapes, or will I start seeing more axis shifts of unknown origin?
Thanks for reading.

Sometimes the motor will slip but it will sound like the belt is slipping. You can check that by making a mark on the drive pulley with a marker or a piece of tape. When the noise occurs is the pulley actually turning or is it stuttering without turning because the motor is slipping? If the motor is slipping, check the current, speed, and acceleration settings. Make sure the grub screw on the pulley is tight, too.

If you have any tension on the belt at all and it slips you probably have a mechanical alignment problem that needs to be fixed. Take the belt off and try moving the carriage or print bed by hand. It should move smoothly and easily without binding. If it doesn't you need to fix it so it does. Then put the belt back on and apply a little tension and try again.

The grub screws are definitely tight, first thing I did was recheck all of them.Realigning the y slightly and increasing the belt tension via the y idler tensioner seems to have helped somewhat. At least right after I did it the print went from slipping y every layer to normal, at least for now. Strange thing is, the x axis was also slipping a bit along with the y, and that seems to have fixed itself as well with the y realignment... Hopefully it lasts. Thanks for that suggestion.

Edited 1 time(s). Last edit at 03/06/2015 05:35PM by anvoice.

Seen the same thing before and like digital dentist said it was the motor actually, and mine was because the belt would bind up just a little causing the motor to make a sound like it the belt was skipping. I put paint marker line on the belt and pulley to test it out.

The fix for me was to loosen all the pulleys and get it sliding smooth and then tightening them all down.

Edited 2 time(s). Last edit at 03/09/2015 03:29PM by AquaticsLive.