A selection of lathe change wheels for Harrison L5 lathe. My tech whiz son http://www.thingiverse.com/logan12358 has edited the original files to work with Customizer so that you can readily make a gear with any number of teeth you want. You can also tweak the bore and keyway settings to optimize the fit.
I have made an extensive array of different sizes of change wheels using PLA and find them to be quite durable and much quieter than steel - just don't run two plastic gears together.
See this thing http://www.thingiverse.com/thing:37795 for a good description of the calculations needed to convert diametral pitch to the right numbers for the Frost library that this code has incorporated to generate the gear teeth.
I printed with 0.3mm layer height and 80% infil and found this worked well. I stopped the first print after a few mm build height and used that as a test piece to check the fit on the lathe. Tweak bore and keyway settings to make it fit well.