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Z-offset plugin -- can't take a negative value

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Posted · Z-offset plugin -- can't take a negative value

LOVE the Z-offset plugin by fieldofview. The idea of having the Z-offset set by the profile instead of me trying to remember to do it when switching filaments just tickles me.

 

But... it can't seem to take a negative number. Cura (3.6) gives a error that it is unable slice "due to some per-model settings".

 

My Z-axis homes with a BL-Touch, I believe which is why I need to use a negative value, since it's homing from above the bed instead of below. I might be wrong.

 

Full disclosure, I am using an Ender 3 and not an Ultimaker. Hope this doesn't get me thrown off the forum. But this is where I saw that fieldofview hangs out.

 

Thanks.

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Posted · Z-offset plugin -- can't take a negative value

Never mind. I found an adjustable mount for the BL-Touch so I can lower it enough that my Z-offset becomes zero for PLA and a positive number for PETG.

 

Sorry to bother.

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Posted · Z-offset plugin -- can't take a negative value

The minimum value for the Z-Offset is the negative of the Initial Layer Height. If the Initial Layer Height is 0.3mm, you should be able to enter -0.3 as the Z Offset.

 

Specifying a value lower than (- Initial Layer Height) would result in a negative Z value in the gcode. The firmware would - at best - ignore the negative value, or give you an error. The firmware assumes that Z=0 means that the nozzle touches the buildplate. A negative Z would mean that the nozzle is below the top surface of the buildplate (ie: the nozzle pushes through the buildplate). Needless to say, the nozzle actually pushing through the buildplate would be "less than desirable".

 

PS: fieldOfView is known as @ahoeben on this forum.

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Posted · Z-offset plugin -- can't take a negative value

PS: you are more than welcome here. No need to apologise (for your printer or your question)

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Posted · Z-offset plugin -- can't take a negative value

I understand a negative Z offset might cause issues with some firmware, but would it be possible to enable it, but with a warning and highlighted in red? 

Reason being, with Chitu a negative offset works perfectly fine and is incredibly useful for tuning the first layer height in conjunction with an ABL. I can position the inductive sensor much lower causing it to trigger with the nozzle much higher above the bed (+4mm), which works well for glass. The higher nozzle height also means any blobs of filament will not interfere with the bed during mesh leveling. 

 

I'm currently manually changing the G-Code Z offset to a negative value but reading through forums it seems like quite a few users have asked about this same issue of having a negative Z-Offset to setup their ABL. 

 

Or if you know of any other methods I could use to edit the G-Code it would be greatly appreciated, thanks. 

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Posted · Z-offset plugin -- can't take a negative value

Vesley,

I'm not the author of this plug-in, I only posed the issue where I, like you, wanted it to accept a negative z-offset. 

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Posted · Z-offset plugin -- can't take a negative value

Sorry, I was directing that query to @ahoeben.

 

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Posted · Z-offset plugin -- can't take a negative value

Let me reiterate that the plugin does in fact accept a negative value, but it is limited to the negative of the first layer height. IE if your first layer height is 0.3 mm, then you can enter -0.3 as the Z Offset.

 

I really don't want to deal with people complaining that this plugin broke their printer/scratched their beds. The plugin is not meant to fix improperly calibrated beds; it is meant to make minimal adjustments to improve bedadhesion. If you want to handle a 4mm offset in your calibration, then you are going to have to do that in your start gcode snippet.

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Posted · Z-offset plugin -- can't take a negative value

Apologies, I didn't really consider the full consequences, but you make perfect sense!

 

Yes, it does work for negative values up to the layer height thickness but I'm currently running it much higher. 

 

I think I should be able to edit the G code so it's negative -4.5 which will then allow me to use your script to bring it up to the correct positive level, so I can have different initial layer heights for different profiles.

Thanks for pointing me in the right direction, really appreciate it!

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