Print Shifts after First Layer

Recently, I've noticed that my prints have start to shift a bit after the first object layer. By "shift a little bit," I mean that starting at the second layer, the print head seems to print the object from then on with about a 1-2mm shift on the Y-axis. After this first layer shift, the print finishes fairly well. The shift happens regardless of the gcode having the base layers (raft) being turned on or not. It's always the first layer of the object to be printed.
Has anyone else had this happen to them or would have any suggestions?

Thanks,
Chad C

Correction...
both the X and Y axis shift on the first layer..

It prints the perimeter fine then when it starts doing the infill, it moves over and ruins the print quite quickly.
Chad C

Edited 1 time(s). Last edit at 01/24/2011 12:03AM by Chad C.

Kind of hard to tell from that picture, but I'm guessing that either your stepper motors are skipping steps because the toque is too low or your pulleys are slipping.

If the pulleys are slipping, use a couple drops of super glue to lock them in place. Don't let the glue run down the motor shaft and into the motor!

If the torque is too low, try adjusting the trim pot on your stepper drivers so that it drives the motor harder. Make sure you don't increase it too much or you will overheat the stepper driver chip.

The x and z axis were both loose but i couldnt get the y axis pulley off so i assumed it was fine.
The stepper control boards have also slowly lowered their power setting over time i believe as they were a bit underpowered.
i corrected both of these and it seemed to fix the problem.

Thanks for the help,
Chad

I have a similar problem except it occurs every 15 layers or so. i have mendel-parts.com electronics and nophead's RP parts, how might i solve this? I haven't changed firmware at all nor messed with skeinforge yet, i'm just using repsnapper so far.

Loose pulleys, motor current too low or perhaps blobs of plastic catching the nozzle.

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