01/25/2018 at 00:10 •
The whole design is drawn in Fusion 360, as anyone familiar will have guessed from the sketch screenshot.
Initially, I started to copy the geometry by taking a best-effort orthogonal photo of the original drive splines, importing that into F360, scaling it, and drawing over it. That quickly proved more trouble than it was worth, since the geometry is, in the end, relatively simple.
Once the image-based copy attempt proved fruitless, I just used calipers to take some very accurate measurements, and a few other best-guess style measurements. Namely:
1) diameter of spline valley to valley (minor spline diameter)
2) diameter of spline peak to peak (major spline diameter)
3) observe that the valleys and peaks appear to be semicircular and not some other more complex geometry
4) observe that the spline pattern is perfectly hexagonal
5) draw control points at all the measured peak and valley centers
6) draw semicircular arcs to intersect those control points
7) shrink by a small offset (.15mm) to account for tolerance of manufacturing on both parts.
Initially, I'd hoped that I could simply shrink the large spline shape with an "offset" command, but that changes the peak and valley geometry quite substantially to be non-semicircular. A version of this I believe worked almost-well-enough, but it was very sloppy. Ultimately, I performed roughly the same steps as above to come up with the smaller spline pattern, and I simply extruded the gap between them.
That's the part I'm using now, but I did observe that putting the motor on the blade can be difficult if the blade isn't pre-clocked to be close to the same rotation on the drive and shaft sides. To handle that in the final version, I added a bit of chamfer. Most 3D printers will only reproduce this to a limited extent, but any chamfer in the output part will prove helpful.
Overall, this was a fun experiment in reproducing geometry of a physical part, and I've now got a bunch of blender parts that work together instead of existing in my cabinets only to cut me while reaching for things.