Setting the Z Probe

Desperately trying to zero the printhead, what am I doing wrong here?
My understanding is that using Pronterface sending the G92 Z0 command should define Home (as long as the power is on)
The Get Pos do respond as expected with Z:0.0000
..and yet the Z Home command crashes the printer head in the same position every time nomatter where on the Z axis I define Zero?

Erik

You are defining a home position, with G92, then telling it to 'Home' afterwards? You don't need to Home - you've already told it where that is. Home doesn't take it to the home position; it tries to FIND the home position, using the parameters you have set - eg setting G31 Z1.8 P656 means that is moves the Z axis down until the proximity sensor reads 656, and sets Z to 1.8mm, then moves down 1.8mm to Z=0. This is the homing sequence. If you haven't set these parameters, re-read the 'Setting the Z Probe' section of the 'Axis Compensation' instructions.

Ian
RepRapPro tech support

for my understanding:
when I use Z home and the printer head crashes into bed, I can move Z manual to the corrct position and send the command G92 Z0, the systems accept this as new z homeposition rather the position that come from the z home sequence?

thank you
helm

@new-3D and Ian

Quote

eg setting G31 Z1.8 P656 means that is moves the Z axis down until the proximity sensor reads 656, and sets Z to 1.8mm, then moves down 1.8mm to Z=0. This is the homing sequence. If you haven't set these parameters, re-read the 'Setting the Z Probe' section of the 'Axis Compensation' instructions.

... I have the opposite issue. With say the G31 Z1.8 P656 command in my config file the Ormerod homes correctly, but due to variations presumably in the z height sensor or the ambient lighting, my probe is too high.
Using Pronterface I use the z move at 0.1mm until it is in the correct position (sheet of paper thickness) away from the printing surface.
Do I need to issue another G command for this position, or just print from here?
I 'think' in the past I just continued my print (via USB from file) and this was successful, but it would be good to clarify.

@new-3d: well, it *shouldn't* crash into the bed, if it's set up and working correctly, but that method works, and is fine (if a bit 'manual')

@Treth: If the Z homing is too variable, due to ambient light or some other issue, that's a problem, because consistency is what we're striving for, especially for the first layer. We'll be looking at improving the proximity sensor in the New Year. But yes, move the Z axis to the correct height, and set G92 Z0. The bed compensation should still be working - remember to load it before starting to print.

Generally, for *really* good first layers, it's worth setting the bed height with the bed at temperature; there's can be a bit of movement in the bed as it heats up.

Ian
RepRapPro tech support

Quote
Ian
@Treth: If the Z homing is too variable, due to ambient light or some other issue, that's a problem, because consistency is what we're striving for, especially for the first layer. We'll be looking at improving the proximity sensor in the New Year. But yes, move the Z axis to the correct height, and set G92 Z0. The bed compensation should still be working - remember to load it before starting to print.

Generally, for *really* good first layers, it's worth setting the bed height with the bed at temperature; there's can be a bit of movement in the bed as it heats up.

@Ian, many thanks for clarifying. Good point regarding the bed heating up.

Sounds like I should turn on the bed heater and let it come to temperature in setbed.g, between homing the axes and running the auto bed levelling procedure.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].