A project log for Concrete CNC

This is an attempt at a cheap but rigid CNC machine (budget approx. 2000€)

David RisbergDavid Risberg 11/24/2020 at 14:202 Comments

Would you believe it? It's actually finished and was used for a first project yesterday! I don't even want to check how long ago it was that I started this project. Far too long...

There are no visible differences to the last log post (except for for a retractable arm holding the interface laptop), so instead of another picture I'll start with some video action:

First ever project was pocketing some hardened stainless steel. After a few slight issues the end result turned out amazing. Zoom in on this picture to see the surface finish:

I'm really happy with the rigidity and minimal backlash of the machine, it handled this tough material well. The only real disappointment was the milling spindle. I knew a cheap high speed spindle would have issues machining steel since it requires lower RPM and higher torque than aluminium or plastic. But with a 2,2kW spindle I didn't think a 5mm endmill would present such a challenge.

Still, I expect I will mostly be milling aluminium and hopefully it will rip through that like butter. The recommended speed range is 8000-24000 RPM, and I was trying to cut at 4400 RPM.

And with that I declare this project completed! Although I may still post more logs with upgrades, modifications, or maybe just to show another milling project. This started out as one of many big projects I have initiated, but ended as one of the few I actually finished. Fantastic!


morgan wrote 11/24/2020 at 19:12 point

How do you make your Single Speed even lighter? Build a concrete mill of course.

Nice build and  nice to see FreeCAD adaptive milling in use, I don't think I've used that part of Path WB yet.

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David Risberg wrote 11/24/2020 at 19:41 point

Haha yeah, that's pretty much how this happened. Although I originally started building it for another project, to make impellers and other components for an electric surfboard. Stupid thing to do, the surfboard project stalled partly because of it so all I've ended up doing is this sprocket. Time and money well spent!

I was very pleased with the FreeCAD path module. It took me maybe 30 minutes to figure it out and create the operations both for alignment marks and pocketing, despite not having used it before. Great that they have adaptive milling as well, it really is the way to go to increase speed and extend tool life in roughing operations.

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