Z offset is not correct
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We are using a Modix 3D printer with the Duet 2 Ethernet board.
I am following the set up instructions on the Modix site.
I touch off the BL touch sensor, then touch off z offer calibration (using a price of folded paper between the nozzle and the bed).
At that point I'm given a number to enter in the G31 line for the z offset (which should be the difference between where the BL Touch probe triggers and the tip of the nozzle, as I understand it).
When I run a print, the nozzle is way too far from the bed to make a print, usually around 2.5 mm rather than the .3mm that it should be.
The people at Hartsmart who sold the machine, so far have no answers.
Can anyone here figure out what might be wrong? -
You need to determine the value for the Z Trigger Height parameter for the G31 command used to configure the Z probe.
One way to do this is with an object of known height, say a precision 1-2-3 block or something similar.
Let us say the height of the object is precisely 10mm.
- You place the object on the bed under the nozzle.
- You jog the Z axis until the nozzle is just touching the block.
- You execute a G92 Z10 command setting the logical position of the Z axis to the 10mm height of the object.
- You execute a G30 S-1 command which probes the bed and reports the trigger height.
At the point you have the value needed for the Z Trigger Height parameter of the G31 and can edit it into your existing G31 command.
Or you could execute a G30 S-3 command instead of the G30 S-1 command. That variation actually updates the Z Trigger Height setting of the Z probe.
To persist that change you would need to execute M500 P31 and have a M501 as the last command in your config.g file.
Frederick
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@fcwilt ok, a bit over my head, but the probe height is entered first per the instructions provided by the machine maker, then the z height.
Point is I get a difference number that I enter, but it's as if the machine ignores it.Our workaround is to start a print, then stop it, and measure the height of the nozzle from the bed. We then change the z offset by that amount, minus the .3mm we need to be from the bed. It works, but it's not right and would like it to work properly.
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You can always determine the Z Trigger Height parameter value for the G31 command by trial-and-error.
Starting with whatever value you have and change it. A larger value will move the nozzle closer to the bed, a smaller value farther from the bed. Change it by 0.1 mm each time.
Of course you have to reboot or reset the printer to get the new value to take effect.
And of course at some point you have to execute a G30 command at the center of the bed to to insure that Z=0 has the nozzle just touching the bed.
Frederick
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@fcwilt yes, that's what I have to do,
I'm wondering why it doesn't work the way it's supposed to though? -
@ritz said in Z offset is not correct:
@fcwilt yes, that's what I have to do,
I'm wondering why it doesn't work the way it's supposed to though?Do you have a link to the instructions you are following?
Most any approach has to do what I outlined, in one form or another.
You first have to have a reference dimension that is independent of the current probe settings.
I use a 1mm thickness gauge but a piece of paper is commonly suggested. The problem with paper is that it deforms and can give false readings. Something like my thickness gauge will not deform.
The reference dimension allows you to set the physical Z position to a known setting. Then you sync the logical Z position to the physical. Then you measure the probe trigger height.
Frederick
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Where on the bed surface are you measuring the trigger height?
Where on the bed surface is the probe using to actually home the Z axis with the probe?
Where on the bed is the print physically placed?
If all three of those locations are different, they should be made the same.
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@ritz One mistake I see is people keeping the negative modifier in the G31 value, as the default value we provide with the printers is G31 Z-3, just so that in the initial setup it
So if you'd for example get a value of 1.25, from the Z-offset maco, and you don't erase the -, but just replace the 3 with 1.25, you'd get a G31 value of Z-1.25 instead of Z1.25. And with that, the nozzle would be 1.25+1.25 away from the print surface.
You can always reach our support directly at support@modix3d.com, preferably with a copy of your config.g files so we can check that as well.
