The Hell Ya Beller Fun with hot, pointy, sharp, and caustic stuff.

19Jul/150

Dogfooding with FreeCAD Path

"Eating your own dog food, also called dogfooding, is a slang term used to reference a scenario in which a company uses its own product to validate the quality and capabilities of the product"

I have a whole pile of old Altoid tins that I use to store small screws and such.  The tins had migrated into a physical pile on top of another storage container and were occasionally knocked over while I was looking for something.  I thought it would be nice to have them in a rack mounted on the slat-wall.

Laser cut acrylic seemed the natural choice.  The glued finger joints are plenty strong but need to be accurately cut.  Since the project was pretty simple, I decided to try to do the whole thing in FreeCAD including the gcode generation with the new Path module.  I know Path is still incomplete but I've been watching the improvements for months and thought I might be possible.  Here's how it went.

The parts were simple sketches padded to the thickness of the acrylic - 3mm.  The important thing is to make the depth dimension of the tabs match the acrylic thickness and the position match the corresponding slots.

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I used the assembly2 workbench and built the assembly.  Assembly2 is very slick and I caught several boneheaded mistakes that would have cost time and plastic otherwise.

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I used Assembly2 again to make a second assembly.  I didn't set any constraints, I just laid out the pieces to fit on the raw stock in the laser cutter.  This way, if I need to change any of the parts, I can just refresh the assembly and regenerate the gcode.

Next I built the profile operations.  This was the hardest part because Path is very new and only the simplest operations are working.  I ended up with separate operations for each outside profile and each hole.

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I hid the solids and just focused on the gcode backplot. It's very easy to see any problems with operations and make whatever changes are necessary.

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When things started looking good, I tried exporting the gcode and loading it in LinuxCNC. There were a few problems that I could easily have fixed by hand but decided to try automating the process as much as possible.

My laser needs a couple commands in the preamble to set the power output. I copied the linuxcnc_post.py file to my FreeCAD macro directory and renamed it laser_post.py. For FreeCAD to see it as a post processor, it needs that name format. The first part can be anything you want but it must end with _post.py. Editing was just a matter of pasting the lines into the preamble section.

At this point, I could select the project node in the tree and use the export menu.  Select 'GCode' for filetype and give it a name.  FreeCAD will prompt with a list of post processors.  I select my new customized post, and click 'ok'  The code is written and ready to be loaded in to LinuxCNC.

That last part is a lot of clicks and I tend to repeat it many times as I'm working out the last little bugs.  FreeCAD has a couple conveniences to simplify things.  The project node has a property for the output file and the Machine node (see picture above) has a property to pre-select the post processor.  With these set, you can click the 'Post process' icon on the toolbar and it's done!

The pieces cut out beautifully.  I glued them together like so:

IMG_1547

 

This was a quick one-day project while I was cleaning up the workshop.  The toughest part of a project like this with my other tools would be the fine tuning to get the slots and tabs to align right.  With FreeCAD, that was really easy.  The Path workbench still has a long way to go and it's not usable for anything but the simplest operations right now, but it's improving fast.

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