Laser Cutting Printrbot 3D Printers via Inkscape
I support a host of laser cut Printrbots including a Printrbot Jr, Printrbot LC, Printrbot Plus and Printrbot Makers kit. These printers vary widely in condition. The Printbot Jr was used extensively for demos and is in rough shape. Several of the printers were assembled by students last year. Over time, laser cut wood can crack, break or warp. Assembly by inexperienced makers is also hard on wood cut parts. I need to be able to repair and upgrade these printers.
Luckily, the Printrbot printer designs are open source and the plans for the printers and upgrades are available on YouMagine. https://www.youmagine.com/users/printrbot The files for the laser cut pieces are in DXF format.
Unfortunately, whenever I have tried to import the DXF files into the open source vector program Inkscape, the files looked to be incomplete or corrupt with line segments missing. I’ve hit this road block before and was usually able to find or make a 3D printed part. Unfortunately, almost all the laser cut Printrbot printers I support are now in need of an overhaul. Laser cutting replacement parts is a top priority. Looking online I found reference to others having problems and having to create their own part designs from scratch. I assumed there was something wrong with the published DXF files. Digging deeper, I found that the problem was that polylines in the DXF files weren’t being imported into Inkscape.
My guess was that the Printrbot designs were created in a commercial CAD package and that a proprietary file format was being exported to DXF for the community. I was frustrated that I couldn’t use open source software tools to prepare part designs for laser cutting. When I tweeted about the problem, Printrbot replied back that the files needed to be converted from Adobe Illustrator.
Realizing that Printbot was using Illustrator, I was able to open the DXF file in my school publication lab using Illustrator CC and all the lines were complete. I ran a 2D print of the file and the outlines matched an existing part. I quickly converted the file to SVG format and moved on. Scalable Vector Graphics, SVG, is the native format used by Inkscape. Later, I opened the file in Inkscape and prepared a cutting plan for an Epilog Zing laser cutter. Preparing the file involves matching the document size to the bed of the laser cutter and setting the line widths for vector cuts to 0.001″. I cut the parts on the laser cutter but they were too small and they didn’t fit together. I haven’t used the laser cutter in a while and figured I did something wrong so went through the process a second time. Again, the parts were too small. I was frustrated. I printed a 2D copy of parts from Inkscape and compared to the print out from Illustrator. Somehow the Inkscape version of the SVG file was smaller than the Illustrator version!
Note: The Printrbot designs typically have ~6mm square holes for connecting the 6mm thick plywood. These can be used as a quick reference for checking scale.
It took some digging to find a forum entry that mentioned the sizing issue. Adobe Illustrator assumes 72 dpi while Inkscape assumes 90 dpi. https://forums.adobe.com/thread/1397645 . Scaling the files by 125% in Inkscape created correctly sized parts. I was then able to laser cut parts that fit together!
Having access to the open source Printrbot 3D printer designs and a school laser cutter empowers me to maintain the fleet of printers. Student researchers are empowered to modify the printers to fit experimental print heads and attachments based off the original dimensions.
My school has an Epilog Zing 50 watt laser cutter. I used 6mm plywood available in 2’x1′ sheets from AC Moore. These plywood sheets fit perfectly on the print bed. The K12-Fab Labs group recommends looking at the Full Spectrum 5th Gen Hobby Laser https://groups.google.com/forum/#!topic/k-12-fablabs/d0cWAZxJ51w.
You don’t need a laser cutter to benefit from these files. You can import the SVG files into 3D modeling programs like TinkerCAD and 123D Design. You can then extrude these shape and create assemblies that will print in a single model rather than multiple lasercut pieces. You can also use the original designed pieces and create modifications. You may need to create offsets when 3D printing the files as there is a small kerf in the laser cutting process which makes the part slightly smaller than the outlines.
Note: I converted all the Printrbot DXF files on YouMagine to SVG and sent the files to Printrbot. Hopefully, other educators/makers/hobbyist using open source software like Inkscape will benefit from the converted files.