I work in a community Fab Lab where we offer laser etching and cutting services to the public. My problem is that we need to use Inkscape to send both rasters and vectors to an Epilog Laser cutter. The files need to be accurate in the real world - not the pixelated world.

To see the issue, I create a rectangle in Inkscape and size it to 100mm x 100mm. It prints accurately to an ordinary inkjet printer, but scales up by 25% to our Epilog Laser. (Yes, after saving as a PDF and printing from Adobe reader).

You don't have to have a laser cutter to see the issue. Just open the SVG file in Illustrator and it's 25% bigger there too.

I have done heaps of searching and it seems fairly well known that Inkscape stores SVG file dimensions in pixels assuming 90 DPI, and when the laser converts the file to print it, it uses 72 instead of 90 - thus creating a bigger output than expected (90 is 25% bigger than 72).

I have seen the suggestion, "just scale the image down first". This would mean that we have the situation where a 100mm dimension has to start out as 80mm in order to arrive at the right size. That doesn't seem right.

I have also seen people submit modified versions of the units.xml file in the share/ui folder. I have tried this but cannot seem to get a meaningful result. In fact I have tried modifying mine quite extensively and cannot seem to make any change to Inkscape's behavior at all.

Can anyone please suggest how I can get a 100mm square (for example) to print at 100mm on a laser cutter (or even open in Illustrator as 100mm, not 120mm)?

Thanks Heaps
Tonez.

Howdy,
I often send Inkscape files to Epilog cutters via PDF without scaling issues. I understand the problem, but I'm unsure why your result is different.

I tested opening files (the same image Inkscape SVG and PDF) in Scribus: SVG was scaled as you describe, PDF was not.

My workflow is often CAD>DXF>Inkscape>PDF>Epilog, but occasionally Inkscape>PDF>Epilog. (WinXP) I regularly work in inches or mm.

What does the PDF reader indicate for image/document size?
What size is the PDF if opened in Illustrator?
What OS, Inkscape version, Cairo version, Adobe Reader version?
Can you provide sample SVG and PDF?


Regards,
TD

Well, wouldn't you know it! I can no longer re-create the initial problem.

Now, when I create a 100mm square in Inkscape, it scales up as an SVG, but as a PDF it's the correct size!
This is not what we had before. The PDF was also scaled up. I know this because we always create PDF's (otherwise the Epilog Laser cutter won't recognise vectors) and they were printing too big (by 25%).

I won't actually know for sure until I get back to the lab in a couple of days, but the PDF file now opens as the correct size in Illustrator - so I'm expecting it to also print on the Laser at the correct size.

Thanks for your response Tyler. I'll keep you posted.
Tony.