Unknown origin Z offset

Hi everyone!

A few days ago, I finally got quality prints on my Prusa Mendel after months of calibration using much of my free time.

To celebrate this success, I decided to print a box for my RAMPS. I didn't notice how high it was and hit the Z height soft limit during the print. After clenching my teeth in frustration, I decided that it would be a great occasion to switch from my old Sprinter to Marlin FW, as I heard much good of it. After many problems unrelated to this post (bad comments in the config file), I got Marlin to work and started a first print with it, and worked successfully with minor enhancements from the same object printed with the old FW.

I then decided to speed up the printer a little (it was on very slow mode), enable GCode arcs and update the firmware with minor corrections (like Z soft limit). Obviously, things went awry.

Now, when a print starts, the first thing the printer does after homing (at low Z endstop) is upping the Z axe a few millimeters. Yes, I had a soft Z offset, of 0.03 mm. This adds about 2mm of Z height! Falling back to default slicing settings, (no Z offset, no lift, slow speed) and it still does the same thing. I reloaded my old firmware, and it happens again.

I have absolutely no clues as of why this is happening. So far, I did undo all my steps (well, I think so) and this keeps happening.
This might be a very stupid and trivial error, but I can't find it!

I'm using Pronterface with Slic3r.

Anybody got any ideas about what could cause this?

Thanks!

Dan

Edited 1 time(s). Last edit at 05/15/2012 12:43PM by N0M4dIC.

Look at the g-code itself, is Slic3r instructing your printer to do this, or is it doing it without any specific commands to do this? If Slic3r is doing it, look in the advanced g-code tab at the start g-code sequence, perhaps that got adjusted?

It seems Slic3r is the origin. Modifying the Gcode to avoid all Z height gain proved effective. I also noticed that slic3r was instructing an offset of 0.33 mm. It also seems slic3r is adding the layer height (0.3) to the Z offset (0.03). Modifying these parameters proved this. As I understand it, I would now need to adjust my Z height to the absolute Z zero or use a negative offset to compensate for my actual Z endstop position. I'm trying this now.

However, if it was working before, what changed?

Thanks.
Dan

EDIT: Inverting Z compensation values seemed to work. I have some new minor calibration to do, but well...

Edited 1 time(s). Last edit at 05/15/2012 01:33PM by N0M4dIC.