Prusa won't get calibrated

Hi there,

After 2 Weeks of calibrations i finally think i need a few hints.

First of all my Reprap Setup.
- Sanguinololu 1.3a with Sprinter Firmware 52f7f30
- ABS Prusa parts with LM8UU Ballbearings
- Mechanical Endstops
- Polyurethan (PU) T5-Toothbelt 5 mm
- 0.5mm GRFF / Wades Extruder
- 42BYGH4803-04 Steppers

I tried to calibrate the X and Y Axis with a digital caliper to run smoothly 100mm.
The Extruder was calibrated to extrude 10mm and the Z Axis to run 50mm.
I got it to work within 0.1-0.05mm tollerance, but if i let the Axis travel for example the half or double way it gets more and more inaccurate.
(See Attached calibration.xls for more details)

Do you have the same problems?
Does somebody knows a fix for that?

I calibrated the Pololous with following method.
1. All potentiometer to the lowest value.
2. Go up until the motors stop jittering and run smoothly
3. Add 1/8 turn.

Best Regards,
Boulway

Either backlash or missed steps can make it very difficult (if not impossible) to calibrate.

For measuring backlash, LashMaze is quite useful.

For calibrating X and Y, I print a 100mm x 100mm x 1mm hollow square, and then measure it both for distance and for square, while it is still on the printbed, and before it has too much of a chance to cool.

For calibrating the extruder, I remove the nozzle, and then run 100mm of filament back and forth until I get it to within 1/2 mm.

Hi Raldich,

I modified a few thinks on my Prusa yesterday.
-checked if ballbearings running smoothly
-oiled the smoothrods
-tightened the Z Axis mounting
-installed Marlin Firmware

After i calibrated the X Axis it looks a lot better.
It seems that you are right with the backlash. The motors are not loosing steps but seem to travel 0.01 - 0.03 more or less each turn.
But this constantly.

I will print the LashMaze at the weekend and give you more feedback.

Best Regards,
Boulway

Double-check the pulley. With the motor powered, is it easy to turn the pulley a small amount back and forth? If so, tighten the set screw.

Double-check your belts. They should be tight enough that when plucked, they make an almost musical note (think bass guitar).

With the motor turned off, slide the carriage back and forth and feel for tight or rough spots. If the axis rods aren't perfectly parallel, it will cause binding.

The easiest way to check for lost steps is to print a 20mm cube. If the sides are slanted, or wobble about by more than .5mm, then you're losing steps.