I decided that I was going to make some stocking stuffers for my great-nieces and nephews for Christmas. I got the STL files from Thingiverse for 3 point, 4 point, and 5 point fidget spinners that use 1/2-13 nuts for the weights and started printing. The 3 point spinner looks like a ninja throwing star. It looked cool, but I had print issues with the points wanting to lift of the print bed, so I re-designed it to be minus the points - no more lifting issues.
I didn't want any little fingers getting stuck in the threads of the nuts, so I designed a 1/2-13 plug that screws into the nut to make them finger-safe. This was the first time I had tried designing a 3D thread, so it took me 5 different prototypes and more than that many hours before I got a version that worked. I have discovered that it's a stone cold bitch to design an imperial thread using a drawing package that thinks in metric, consequently I'm fairly proud of that 1/2-13 plug.
It took me a while to convince myself, at least 4 prototypes, that the design for the plug was correct. The thread spec's were correct, but on the first couple of prototypes I had been applying the internal thread specs' to an external thread - the root radii are different. I eventually determined that the stinkin' printer was printing about 2% oversize. Up to this point I had always had fit issues between parts that usually required some fettling to get them to fit - this 2% oversize discovery explains those problems away. I thought it was just the way 3D printed parts were going to be, and was happy just to be able to get the part to print. I am now printing a prototype at 98% scale and checking fits before I move on to the next part.
I don't have any pictures right now, so I know that this adventure obviously didn't actually happen. But, if anybody wants to see the parts, I'll take a family shot tonight when I get home and post it tomorrow.
Don