Lightburn 2D shape vs DXF

Friends, A penny for your thoughts:

  1. Create a circle.
  2. Export circle as DXF
  3. Import DXF back to Lightburn
  4. Cut both wih same settings

Lightburn native circle cuts through nicely vs the imported dxf of the same circle which does not. I would have guessed this is due to DXF format which includes many more line segments but this is not the case with perfect circles.

Right one is the re-imported circle as DXF

Please enlighten me.

K40 & Gcode.

Ran some more tests. Looks like Convert to path is the culprit.
Imported DXF As-is: cuts through clean
Imported DXF > Convert to path: does not cut as clean and leaves a thin layer of wood which makes it harder to push the parts out of the playwood. feels like running 30% slower makes both shapes cuts evenly.

Still investigating.

Tried to duplicate what you did. LB DXF exports DXF circle entities, and also imports them as “ellipses” with “Rx” and “Ry” equal. Whether I convert 1 circle to a path, or leave it alone, and save Gcode for both entities, I get the exact same results when I look at the Gcode. The start points of each shape are different, but each shape has the exact same number of facets to recreate the circle.

‘Convert to Path’ shouldn’t actually change anything - it just takes the already generated path and switches the object from being a dynamically generated circle (4 splines) to being a path object that’s just those 4 splines.

Hi Ralph,
Interesting. Obviously there are differences cause native circles cuts clean at 20mm/s and DXF at 10mm/s - quite a big difference.

I Just saved 3 gcode files

native 20mm circle
dxf 20mm circle
dxf converted to path

it does looks like path and original dxf are same files. very interesting cause my physical results are different. maybe my issues is not the convert to path but with native shapes and dxf. huge difference - twice the time to cut dxf files.

I guess I need to run more tests.
I must understand why my DXF projects needs to be cut at much slower speeds.
I ran into this issue during a big DXF based project. i replaced drill holes with native circles and the outcome made me wonder what goes on.

A lot depends on what program created the DXF code. LB DXF export creates short line segments that approximate arcs, and all shapes are defined in DXF as polylines. It also exports DXF circle entities. When LB creates Gcode, it does the same thing, except it also facets the circles. The Gcode export and DXF export (less the circles) is pretty similar. If you are importing DXF files into LB that contain faceted polylines or splines with a lot of line segments, that can also be a problem.

I have created a rubber band shape and export/import as dxf. I will later test and see how these two behaves and report back.

Upper shape is native LB rubber band
Lower is the imported DXF.

The upper / native just drops off clean, the dxf still bites to the plywood and holds in place. not by much, i can force it out but there are differences which I like to know why.

I recreated your shapes, and exported the bottom shape to DXF. Deleted the original bottom shape, and DXF imported the bottom shape I exported back into LB. I then created a Gcode file of both shapes. When I look at the code, the number of facets on the larger arcs is 16, which is the same number of facets from the imported DXF file. Maybe check that the shapes are both being cut in the same direction - clockwise vs counter clockwise.

Thanks Ralph. you taught me some new terms. I will run some more tests. I really like to get to the bottom of this and if this is a smoothie firmware and/or hardware that is to blame. I do tend to break shapes and rejoin shapes to fix bad/broken dxf files so the laser head will not jump around. It will help to know if Smoothie somehow changes the laser power during specific segments / shapes.