I wanted to try out AutoDesk 123D for designing parts to be 3D printed on the RepRap, so I designed a holder for a Dremel Flex-Shaft so I can mount it on my Zen Toolsworks 7x7 Mill.
Drawing the model in 123D was fast and easy. I'm looking forward to using it for other things. I constructed this by starting a sketch in the XY plane and drawing the long rectangle, the two concentric circles for the holder part, two three-point arcs for the fillets (it may be able to do that automatically, I didn't experiment with that), and a couple of rectangles for the tabs. The sketch lets you multi-select the areas defined by the lines, so you can then extrude just the parts of the sketch you want. For the horizontal holes I started sketches on the faces where the holes needed to be (just a circle), then push/pulled it through the solid. Very simple construction process, and it maintains all the sketches and push/pull operations in the Browser, so you can easily go back and change them later.
I drew all the holes to the exact size. I know that the RepRap typically makes the holes a little small, but I wasn't sure if it would be better to draw them a little bigger or drill them out.
Once I had the model done I saved it as a .stl file and got it going on the printer. This is about as easy as it could be. The printer has home switches on all the axes, so it's just a matter of opening the file and clicking 'print'. It takes it a minute or two to warm up, then it's off and printing.
It took about 15 minutes to get both parts printed. They came out pretty good. The horizontal mount holes are only 5mm from the edge, and I noticed that the layers were a little wobbly on that narrow part, but nothing serious. I think in the future I should probably try to provide more material around horizontal holes like that.
I ran a drill bit through all the holes to bring them to the target size. It seems to make them about 0.5mm too small. That works out pretty well because the drilled surface is more precise and smooth anyway. Since the back of the part that mounts to the tool plate on the mill is a bit wavy I decided I'd face it on the mill to make it flat and square with the bottom of the part( which is glass-smooth from the bed of the printer).
Milling the plastic part works pretty well, but you have to be careful to not go too deep. Because the interior of the part is an open network (I'm using 30% fill) you can't cut away very much wall and retain the strength of the part. Also, where the filaments stick to each other isn't nearly as strong as the plastic itself, so if you try to cut nearly through a layer it'll tend to peel off in strings. It's probably best to plan to cut not more than halfway through the filament depth, or possibly to impregnate the part with epoxy (or maybe wax) before milling. I ran the parts on the big mill with a fly-cutter, and other than tearing up a few filaments, the milled face came out great.
Mounting the part on the mill was fast and easy, all the holes were exactly where they were supposed to be, and it was all square and flat. It bolted right up and is good to go.
Fortunately, my Flex-Shaft is the old-style with a simple 12mm tube, so no funky ergonomic shapes to deal with.
I think next I'll make an adapter plate system with some magnets in it so I can quickly swap out simple tools, like a pen holder, magnetic field sensor, touch probe, etc.