Cura Bug: Layer Numbering

[CrazyIvan2 1]

Okay, so it's not critical, but I was viewing a Cura-generated .gcode file with the intention of editing it manually*, and I couldn't make the number of layers add up.

 

According to the preview, the slider on the right went from layer 1 to layer 13.

 

When I looked in the gcode, the ";LAYER:" comment lines went from -5 through 0 to 8.  That's 14 layers.  I couldn't figure out what was going on for a while.

 

Then I discovered there was no ";LAYER: -1"!  It goes -5, -4, -3, -2, 0, 1, 2...!!

 

So, what is the intention of this layer numbering?  Why not keep it the same as the layer numbers when previewing?  I can see the negative numbered layers might be intended to represent the raft or other support, but is 0 the first actual layer or is 1?

 

I know, you're going to ask which version of Cura, but I don't have that info accessible right now.  It's not the recent release, it's whatever was current back in June.

 

* Why would I want to edit gcode?  FreeCAD won't pad disconnected parts of a sketch without them being on some kind of support, because they produce disconnected solids.  The easiest way forward was to put them on a plinth and then delete the plinth from the gcode.

[Slashee_the_Cow 418]

1 hour ago, CrazyIvan2 said:

So, what is the intention of this layer numbering?  Why not keep it the same as the layer numbers when previewing?  I can see the negative numbered layers might be intended to represent the raft or other support, but is 0 the first actual layer or is 1?

0 is the first layer. There is no -1 because it leaves an air gap between the raft and your model so that you can easily remove the raft.

 

1 hour ago, CrazyIvan2 said:

* Why would I want to edit gcode?  FreeCAD won't pad disconnected parts of a sketch without them being on some kind of support, because they produce disconnected solids.  The easiest way forward was to put them on a plinth and then delete the plinth from the gcode.

Yeah, I %$&^ing hate the single body rule. You can extrude a sketch from the Part workbench, then go to the Draft workbench, downgrade your body (in my case it downgraded into a bunch of faces) and maybe the extruded sketch you just made (you'd have to try it), go back to Part workbench, select all the things, and create a union of them.

 

Or you could just extrude your other sketch using the Part workbench and export the body and that part separately then just bring them both into Cura.

 

Also, unless it only takes up like, a single layer, removing an object from the g-code is incredibly hard, especially if it's been combined with other parts in the slicing process.

[CrazyIvan2 1]

So this isn't a bug but intentional?  Thanks.

[CrazyIvan2 1]

19 hours ago, Slashee_the_Cow said:

Also, unless it only takes up like, a single layer, removing an object from the g-code is incredibly hard, especially if it's been combined with other parts in the slicing process.

Not that hard, once I had identified the relevant layers, because I specifically arranged the supporting plinth to be in layers which were dedicated to the plinth only.

 

I now realise what I should/could have done is leave the plinth in the print and inset an air gap layer between (although consideration would need to be applied to the slicer settings so that there was actually solid print below and above the post-slicer insertion of the air gap).  The air gap could (maybe?) be achieved simply by modifying the z movement at the start of the layer.

[CrazyIvan2 1]

...however I've just realised there is a problem with absolute z coordinates.

 

I (accidentally) worked around that, because I orientated my model in Cura with the plinth at the top, so I only had to delete the final layers.  It turns out that was a good choice!

 

Nonetheless, I see no reason z coordinates could not be dealt with using global edits.

[Slashee_the_Cow 418]

34 minutes ago, CrazyIvan2 said:

Nonetheless, I see no reason z coordinates could not be dealt with using global edits.

I'll definitely concede that one. When you're getting rid of entire layers, yes, that's easy, and there's no particularly good reasons I know of not to do it manually (although if it was me, even if I was only going to do it once, I'd probably write a post processor to do it for me, because I'm sure it'll save me time - or more to the point, I'm just that kind of weird).

It's just removing an object which isn't the only thing on its layer is difficult, even if it's isolated from everything else, because you still need to figure out its coordinates relative to the bed and remove any moves in/to that area without breaking something else in the process.

[CrazyIvan2 1]

28 minutes ago, Slashee_the_Cow said:

I'd probably write a post processor to do it for me

 

I grew up with BASIC and procedural languages.  Writing add-ons to existing software (such as an extension for Cura) is a step too far for me.  My idea of a "post-processor" is an edit script or perhaps something in AWK... or even a spreadsheet.

 

32 minutes ago, Slashee_the_Cow said:

I'm sure it'll save me time

 

I sure recognise that one!