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Problems setting Z offset with new probe (Marlin) [FIXED]

Posted by David J 
Problems setting Z offset with new probe (Marlin) [FIXED]
June 03, 2015 06:28AM
Ever have one of those days when you can't get something to work right, even though you're sure you're doing everything correctly? I'm having one of those days...

My equipment is:
Prusa i3 (much modified)
Arduino/RAMPS 1.4
Marlin (configuration.h file attached)

Originally this setup was working very well, using an inductive probe for self-levelling. When that probe was installed I put the hot-end a paper's-thickness off the build surface, then moved the probe up and down until it triggered at the right point. After a bit of trial and error this has worked very well for many months, but I really wanted to get back to printing on glass as I found that far more useful and effective.
So I took off the inductive probe, fitted an IR probe in its place, and made the appropriate changes in Marlin's configuration.h file to make it work - and it does seem to work OK. I can auto-level and home the z-axis properly.

My problem is that the hot-end prints far too high off the bed. I have set Z_PROBE_OFFSET_FROM_EXTRUDER to a value that, if I send G0 Z0, the hot-end just grips a thin sheet of paper (0.08mm thick). Despite this, when I start to print the hot-end looks to be 0.4mm or 0.5mm off the bed instead of the 0.2/0.3 set when slicing; the filament just drops down and doesn't stick.

I have no Z offsets set in either Slic3r or Cura (I use either via Repetier Host) and, as far as I can tell, I have none elsewhere.

Can anyone suggest a place to look, or any other ideas? I could use some fresh clues!


Edited 1 time(s). Last edit at 06/03/2015 11:14AM by David J.
open | download - Configuration.h (35.3 KB)
Re: Problems setting Z offset with new probe (Marlin) [FIXED]
June 03, 2015 11:17AM
Tried again this afternoon - followed exactly the same procedure as yesterday and (after a few minor issues) the thing worked precisely as it should.

I have no idea what I did differently... but I did put a glass sheet over the heated bed, and I think the IR probe was a lot happier with that rather than the previous 'kapton on aluminium' surface. Maybe it was getting the wrong sort of reflections.

Or maybe I'm just going through the mentalpause...
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