The Design Process
Updated Sunday April 23, 2007
Here's a TurboCAD 6 drawing file of a wheel test board I've created. The tooth profiles are not cycloidal, but a profile called "SPYR" that I recreated free style (i.e. no formula, just made it look like the tooth profile shown), from an image I found on this watch website about 2/3's the way down the page. The mod of the wheels are 1.2, and are the smallest I've been able to reliably reproduce on the scrollsaw. Mod 1.2 is relatively small, and I have to use a #2/0 blade with a 5x loupe mounted on the saw to sight through while cutting, but there's nothing to stop you from scaling it up to say mod 2.0 or 3.0, but if you do, just remember to adjust the studs on the board and holes in the wheels to a standard dowel size. Note: I didn't "drill" the 0.1344" holes (for 1/8" studs) in the wheels, I cut them with the saw. If you drill them, it's hard to get the hole centered exactly. If you have TurboCAD, download the file and give it a try.
Download testwheels TurboCad tcw file (Link will download the 46k file [testwheels.zip])
Below are some photos of the completed test board and wheels. Click on each photo to view a high res version, but please note that the images are somewhat large, so download times may be long on a dial-up connection. (Please note that the wheel in the "saw with loupe" photo was already completely cut-out, I simply re-mated the finished wheel with its scrap to show how it would look if it were actually being cut. Also, some of the wheels and pinions shown in the photo of the "10 wheel test board" (the three in the upper left), and all the wheels in the three wheel board, are actually cycloidal, but the others are of the "SPYR" profile. I found that with the inherent inaccuracies introduced by cutting such a small mod on a scroll saw (or most likely my poor cycloid design), the cycloidal ones would bind, but the SPYR ran very smooth regardless of any variances. All tooth profiles in the TurboCAD file are SPYR.) And yes, my wheels are cut from 0.170" Masonite, but any good quality Baltic or Finnish Birch plywood should work well.
