When I first saw the title I mis-read it and thought it said "turned" parts.
But that's ok, this bit fits either way:
I had a good-sized sprocket that was supposed to go on a crank with a different BCD, so I got a bit of 6061 aluminum sheet and turned an adaptor on my dad's (now mine) lathe. Was a good project, a bit tricky as the necessary offsets to make it flush left little margin for error. Spot the one I did make....
And if anyone is tempted to do the same, remember to take the skin off *both* sides of the sheet, otherwise you'll have unbalanced residual stress, and it'll bow.
(I just posted a photo of the complete bike in the show-us-your-bike-that-no-one-else-has thread.)