Most of the time my Prusa i3 behaves itself. Occasionally it jumps by 2.5-5 mm part the way through a print, only on the Y axis. When it does so there is a sound as though the belt is slipping. In fact this is what I think is happening. I reduced the frequency of this occurring by improving the belt alignment - the original stepper mount was weak and broke very early on IO replaced it with a steel one. Th bed attachment was also causing variable tension on the belt, so I modified that so that the tension remains constant throughout the travel of the bed. BTW the jumps only occur when the bed is near to the centre of travel. I can reproduce the sound by moving the bed backwards and forwards rapidly (when un-powered). Any further ideas greatly appreciated.
All the usual stuff applies. Once you're 100% sure the mechanism is smooth and free of binding, the belt is tight, and the drive pulley is tight on the motor shaft, start playing with motor current and acceleration settings.
Everything now seems fine after I changed jerk from 20mm to 5mm. Now I have another issue, but I'll raise it as a new topic. Thanks for advice, I managed 5 prints with no problems, all of which had had problems before.
