paynterf
Posts: 14
Joined: Thu Dec 01, 2016 9:17 am

Skirt won't print if global z offset is negative and larger than layer height

Sun Dec 16, 2018 10:44 am

Hi,

I've been using a skirt on my small models, and for some reason it sometimes refuses to print. I searched around a while and found a note to the effect that if the global z-offset is negative and the value is larger than the layer height, skirt printing is disabled - WTF!!

Anyway, this is exactly what is happening with me using S3D 4.1.1

I need to be able to freely adjust the global z-offset to accommodate bed levelling inaccuracies, and having to screw around (again!) with bed levelling to work around an S3D problem is very frustrating

Regards,

Frank

horst.w
Posts: 852
Joined: Fri Oct 17, 2014 5:00 pm

Re: Skirt won't print if global z offset is negative and larger than layer height

Sun Dec 16, 2018 3:09 pm

You are right,
it pulls the skirt down under the zero-level. Perhaps it is the last call to have attention to a very unusual situation.
I'm printing any time with negative Z-Offset, -0,12 mm when the layer height is 0,20 (in sum positive)

But it seems that the program doesn't understand why you want to print under the table. Me too.


horst.w
GER

Have a look under my table ...
Offset greater than.png

paynterf
Posts: 14
Joined: Thu Dec 01, 2016 9:17 am

Re: Skirt won't print if global z offset is negative and larger than layer height

Sun Dec 16, 2018 5:34 pm

The problem isn't that I can't SEE the skirt because it is being displayed below the print bed, it is that the skirt ISN'T PRINTED AT ALL.

I would understand if the skirt wasn't shown (or was 'hidden' below the bed surface), but stayed in the G-code and was printed at Z = -0.4mm, which in my case would be right on the bed surface. But I don't understand why it would be in the G-code for Z = -0.1, -0.2, and -0.3mm, but not at -0.4.

Why does the slicer care about the Z offset anyway - it doesn't know where the physical bed is on the Z-axis. I could have my printer set up with the bed at Z = -50 mm (stupid, but...) and it should still print correctly.

Regards,

Frank

User avatar
dkightley
Posts: 2238
Joined: Tue Mar 10, 2015 4:09 pm

Re: Skirt won't print if global z offset is negative and larger than layer height

Sun Dec 16, 2018 5:45 pm

Any chance of a Factory file of an example where the skirt is not printing? It may help with you error report....
Doug Kightley
Volunteer at the National Tramway Museum http://www.tramway.co.uk
Railway modeller and webmaster at http://www.talkingtgauge.net

paynterf
Posts: 14
Joined: Thu Dec 01, 2016 9:17 am

Re: Skirt won't print if global z offset is negative and larger than layer height

Sun Dec 16, 2018 6:55 pm

dkightley wrote:
Sun Dec 16, 2018 5:45 pm
Any chance of a Factory file of an example where the skirt is not printing? It may help with you error report....
Sorry - I re-levelled my bed to get rid of the negative offset, so I'm not having that problem at the moment (and I don't want to screw up my currently-printing-fine setup :-) ). However, the next time I run across it I'll ship you a factory file.

Regards,

Frank
'

horst.w
Posts: 852
Joined: Fri Oct 17, 2014 5:00 pm

Re: Skirt won't print if global z offset is negative and larger than layer height

Mon Dec 17, 2018 2:53 am

paynterf wrote:
Sun Dec 16, 2018 5:34 pm
The problem isn't that I can't SEE the skirt because it is being displayed below the print bed, it is that the skirt ISN'T PRINTED AT ALL.

I would understand if the skirt wasn't shown ...
....

All parts of objects, situated below the digital print table are not printed, they are "brushed under the carpet".

The visibility of parts unter the table is urgently necessary to adjusting things you won't print or set a print angle line.
The transparency of the table is very helpful!


H.

Tipp: If your brim, set nearby with zero mm distance, undercuts the object, it doesn't stand fully on the table!

paynterf
Posts: 14
Joined: Thu Dec 01, 2016 9:17 am

Re: Skirt won't print if global z offset is negative and larger than layer height

Mon Dec 17, 2018 8:00 am

horst.w wrote:
Mon Dec 17, 2018 2:53 am


All parts of objects, situated below the digital print table are not printed, they are "brushed under the carpet".

The visibility of parts unter the table is urgently necessary to adjusting things you won't print or set a print angle line.
The transparency of the table is very helpful!


H.

Tipp: If your brim, set nearby with zero mm distance, undercuts the object, it doesn't stand fully on the table!
this seems to be a major defect in the software. Is there something about this "feature" that I don't understand that makes it a good thing?

S3D-Alex
Posts: 412
Joined: Thu Aug 30, 2018 1:23 pm

Re: Skirt won't print if global z offset is negative and larger than layer height

Mon Dec 17, 2018 11:06 am

Could you please post a Factory File for this? In our testing here we found that the skirt will still print even with a negative Z gcode offset that is greater than the layer height. It is possible your printer is not printing this though as some machines has firmware limitations or software endstops that might prevent a negative value being used for your Z.

horst.w
Posts: 852
Joined: Fri Oct 17, 2014 5:00 pm

Re: Skirt won't print if global z offset is negative and larger than layer height

Mon Dec 17, 2018 5:25 pm

Don't worry! Version 4.01 is the same, if the Z-Offset is negative greater than the layer height, the brim or skirt is going under the zero-line of the print table (and is not printed). It is not a bug, it is a feature!

It is absolutly unusual and it is dangerous to set the z-home to a negative value so that the nozzle becomes deeper than the real print table of the printer.
The bed- distance of my printers are set to 0.10 - 0.15mm and the endstop switch shut down the motor if Z reaches this point. To determine the distance of 0,10 mm I must adjust the tables screws up or down. Also the real printer table stands relatetd to the nozzle in
a negative value. Thats normal!

To print it is easy to calculate:

nozzle distance to bed = 0.10 mm
First Layer Height = 0.20
makes together 0.30 mm
Z-Offset in the G-Code-Tab = - 0.12 mm
effective layer height for the first layer = 0.30 - 0.12 = 0.18 mm

All settings are very well done for the extrusion of 0.20 mm height, so the first layer is well pressed on the table for best adhesion.

H.

paynterf
Posts: 14
Joined: Thu Dec 01, 2016 9:17 am

Re: Skirt won't print if global z offset is negative and larger than layer height

Wed Sep 18, 2019 8:50 am

This is still an issue in V4.1.2. I can print anything I want at any Z-axis value in the Global G-code Offsets dialog in the 'G-Code' tab EXCEPT a skirt/brim - WTF??

As an experiment I used three sheets of printer paper instead of one to level the build plate. Each sheet is about 0.1mm thick, so 0.3mm offset. After leveling the bed, I printed a small project with brim & ooze shield, and found I needed a Z-offset of -0.35mm to get proper first-layer adhesion. With this offset, the brim is displayed below the build plate and doesn't print, although both the ooze shield and the model are displayed and do print. So we have a project with three printing elements, two of which print fine with any Z-offset, and one element (the skirt/brim) that won't print with a negative Z-offset greater than -0.19mm.

So, in order to get the skirt/brim to print, I have to level the build plate without any paper spacing, in order to get the Z-offset down below 0.19mm. Can anyone please explain the logic behind this? Why in the world would the user have to make a HARDWARE adjustment to work around a SOFTWARE flaw - i.e. the fact that the brim/skirt feature doesn't honor the G-code tab Z-axis offset setting?

TIA,

Frank

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