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

[Zenmaniac 0]

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.

[Zenmaniac 0]

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.

[ahoeben 1,965]

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.

[ahoeben 1,965]

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

[Zenmaniac 0]

Thanks. Your explanation makes a lot of sense. 

[Vesley 0]

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. 

[Zenmaniac 0]

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. 

[Vesley 0]

Sorry, I was directing that query to @ahoeben.

 

[ahoeben 1,965]

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.

[Vesley 0]

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!

[Dorian_S 0]

Hi,

 

I'm currently having a related issue to this topic. I use a Creality CR-10s Pro V2 (incl. BL touch system)

I changed my nozzle to a steel plated one and apparently it had generated new issue with the bed adhesion. It wasn't the case before I changed it.

After I changed to nozzle, which seem to be exactly the same dimension as the original, I've done again the bed leveling using the tool to make a gap of 0.2 mm between the nozzle and the bed. After that my prints were not adhering anymore.

 

So I was trying to play whith the Z Offset to squish it to the plate a bit more. Originally it was set to -1.5 already and I was able to push it to -0.4 mm. I tried it gradually and I could see the result a bit improving each time but not sufficient and I could not increase more. The value is in red in Cura 

 

Other param:

Initial Layer = 0.3 mm (i'm still surprised that, having an initial layer to 0.3, it still didn't grip the bed

Filam: PLA

Auto-Leveling of the printer is set to OFF

 

I have two questions:

1) Is there a possibility that the BL touch is causing an issue

2) Is there a possibility to push the Z offset more?

 

Best regards

 

 

 

 

 

 

Cura_Settings.3mf

[ahoeben 1,965]

I don't know about your printer or the BL touch. If you are really committed to trying to fix this in the gcode instead of fixing your printer, then you will have to edit the plugin. The minimum value that is accepted by the plugin is defined here:

https://github.com/fieldOfView/Cura-ZOffsetPlugin/blob/3.5/ZOffsetPlugin.py#L29