Design size is different in Luban than source

[gamemaker]

I need to carve out a quadrilateral shape, with a very specific size. It’s a trapezium - think a rectangle with one sloped side.

File attached, created in Inkscape:

It’s 9mm tall, the top is 20.6mm, and the bottom is 25.2mm

When I bring it into Luban:
a) it imports TINY:

it’s less than 2-3mm tall, looks like
b) the proportions are different (if I scale it up so it’s 9mm tall, then the bottom is over 30mm wide:

If I make it so the blue outline is the correct size, then I get the proportions I want, exactly:

I guess the question is, why is there a margin around the black shape?

Appreciate any help.

[gamemaker]

Hm. Well, I went with it anyway, and it turns out the black shape is NOT actually where it’s going to etch.

I had it generate gcode, and it’s correct - according to my svg file - but it does NOT line up with the black image.

I suspect something to do with the stroke settings in Inkscape, maybe? Weird.

[Atom]

@jepho, I know you have done a lot with cnc, do you think you can explain this? Is it just a bug?

[sdj544]

The file you attached is png not svg, so can’t tell for sure.
I think the problem is with the image in inkscape.
I think you’re right about stroke. I think you have black fill with white stroke over a white background. So while it looks like nothing there, it’s just blending with background.
-S

[jepho]

S has identified the issue partly. Vector lines are always single lines (there is no need for them to be anything else) and bitmapped files will have dimension and stroke as two of their parameters. FWIW, the dimension interpretation in Luban is not consistent with the interpretation in Lightburn. The illustration I have linked shows a laser image in Lightburn on the left and the same image in Luban.

Grayscale not engraving

OK, as I suspected the other software is better… the Snapmaker runs quieter and the results are so much better. [Lightburn vs Luban] This image of two burns says a lot about Luban. to keep within the 98mm square 2mm plywood borders, I set the size of the .svg file to 85mm in Luban and Lightburn. The Lightburn image is on the left and it is much larger than the Luban image, despite both being cut from exactly the same .svg file. The Luban image has a lot of smoke staining but the cut is reaso…

My first port of call is to try a different CNC software. Luban tells you as you open the CNC section that it is alpha software. This may explain the inability to transfer files at the size you expect.

I create all of my designs in vector design software so that I can account for their accuracy. I take my final size of the image and place that on a transparent background to the same X & Y dimensions. I don’t use Luban any more but when I did I made certain not to give Luban the option to adjust the size. I enter the X & Y dimensions of the piece and Luban is forced to produce a design of the correct size.