Advice needed on Z Calibration

Ormerod 2

Have been printing with this unit for a while and mostly all has gone well. Have been having a few problems lately which I believe is because the print head is sitting just a little too high off the bed, as it occasionally pulls the printed filament along with it (as it has not been pressed onto the bed properly), causing high spots that then result in just a big mess.

My understanding was that the G31 command in the config file set the calibrated height for the z axis (e.g. G31 Z2.5 P598), but adjustments I have made to this do not seem to alter the printing height. So am I looking in the wrong place... or maybe I just need to make bigger adjustments?

Thanks a lot.

Ralph

The best is to check your Z zero height manually. Even when the automatic Z zero is working well, I always do a quick manual check before starting a print - it only takes a few seconds once you get the hang of it. Automatic bed probing (if your bed is not level) is not as big a problem, because any height errors are likely to be consistent for all probe points, which will result in the correct bed levelling even if the heights are not 100% correct.

I use a common method of manual height adjustment. (1) ensure the nozzle is clean (no plastic blobs or drips). (2) Do the automatic X, Y and Z homing (the Z home will be over-ridden later). (3) using the X, Y and Z buttons on the web interface or Pronterface, position the nozzle a few mm above the center of the bed. (4) Place a piece of ordinary copier paper under the nozzle. (5) Without touching the bed, commence sliding the paper back and forth under the nozzle whilst lowering the nozzle in 0.05mm or 0.1mm steps using the Z button. (6) Stop lowering as soon as you feel some resistance to the paper movement, but before the paper is gripped too tightly to move. (7) Send "G92 Z0" command.

If the first layer is too high (extrusion not sticking to bed) or too low (extrusion wide and blotchy - extruder skipping steps), repeat the Z homing process as above but allow the paper to be gripped more strongly or weakly than before - you will soon learn what amount of resistance gives the correct height.

Dave

Hi Dave,

Thanks for the feedback.

And for some solid advice. I now seem to be able to get consistent first layers coming out. Can't help feeling this should be included in the main calibration information.

This all came to a head (no pun intended) by the way as I have started using some new filament which, I suspect, is not as good a quality as that originally supplied with the printer. It seems to be very sensitive to the nozzle spacing from the bed - some prints have worked just fine and others have resulted in a tangled mess. It also seems to produce the occasional thicker 'blob' on the print that can then get caught and mangle things up - but that is maybe a topic for another thread.

Am happy to now know how to get the z cal right though - so thanks a lot.

Ralph

Quote
rjmusto
This all came to a head (no pun intended) by the way as I have started using some new filament which, I suspect, is not as good a quality as that originally supplied with the printer. It seems to be very sensitive to the nozzle spacing from the bed - some prints have worked just fine and others have resulted in a tangled mess. It also seems to produce the occasional thicker 'blob' on the print that can then get caught and mangle things up - but that is maybe a topic for another thread.
Ralph

If the blobs are not only on corners, what you describe can be due to water in the filament. The filament is hygroscopic - it absorbs water from the atmosphere. If not kept in sealed bags by the supplier and by the user when not in use, water can accumulate in small voids in the filament which "popcorn" when they get to the nozzle and eject a spurt of plastic. You can dry the reel by placing it in a sealed bag together with silica gel or dry rice and storing in a warm place for a few days.

If the blobs are only on corners you could try lowering the temperature by 5 degrees or so, and might benefit from upgrading to the latest firmware release which has smoother move code.

Dave

Dave,
Thanks once again for the tips - I suspect I may be seeing both of these problems as blobs on corners and on a straight run have been a problem. Slowing down the print speed has helped quite a lot with the corner ones, so will also look at upgrading the firmware.

Ralph