Today’s python programming project: Programmatically generating g-code that makes spherical holes using a flat-ended bit.
My plan is to make a chinese checkers set (on the Shapeoko) and be able to cut nice holes for the marbles to sit in. When I’m finished, this code will take an SVG with elements, and convert it into a bunch of spherical holes of any size.
My other idea is that I could use very similar code to mill a huge magnifying glass lens out of clear acrylic. 
frensel lens could be super cool! I have thought about doing this with my laser cutter… But i am not sure it would work that well as the laser makes it a bit cloudy.
I’ve looked into fresnel lenses a little bit. I don’t think I could control the surface angle that well in small strips like I would have to. If I did a regular lens, I would sand the whole thing with fine sandpaper, then learn how to flame polish it.
Yah I agree.
Very nice idea! Any plans to open source or otherwise make the code available for others to extend the concept?
Can’t you just rotate the axis of the arc commands?
It would probably be faster to just do a toolchange and use a suitable bit though.
@Craig_The_Fabricator I’ll probably upload to github, but I haven’t gotten around to it yet.
@William_Adams If I did arcs, I would have to plunge the entire depth at once. This way I can go down in levels and not risk breaking a bit. I might still figure out how to do some kind of criss-crossing circular pass to smooth out the ridges, but I haven’t figured that out yet.
I’m doing this to make any arbitrary size of round hole. In the chinese checkers example, the best result and most suitable bit would be a 5/8" ball-nose endmill, but that’s an added expense and maybe not something that would work with the Shapeoko.
A smaller ball-nose bit would probably achieve smoother walls, but that would take a lot more calculation to get to where I am now. My current code leaves me with jagged walls, but with the part of the wall that juts out at exactly the diameter that I want (in this case, just touching the marble).
Do a rotating series of arcs, starting at the center w/ a very small one, set to a size == to the bit diameter, then do a slightly larger one rotated at 90 degrees, then do two more of increasing sizes @ 45 and 135 degrees, then work out the math for doing 4 more at 22.5 degrees, 67.5, &c. and continue until you’ve cleared the pocket — once you’re done, a spiral path in to the bottom going clockwise in and then out should give you a decently nice finish.
I believe you could get down to a surface which could be nicely smoothed w/ just a bit of sandpaper wrapped around the end of a rounded off dowel.
@William_Adams Thanks for the ideas. I haven’t tried doing arcs in the vertical plane before, but that would definitely be interesting.