For several months I have been building an engraving mill and not producing any reels. So now I am back on reels, and have to re-familiarize myself with the processes. At the center of the reel is a critical part made of Delrin. It is the bushing for the spool, and it is one piece with the wheel of the clicker.
I have been calling the toothed part a “ratchet”, but that may not be correct. Dictionaries say that a ratchet allows just one direction of rotation. A clicker has to allow bidirectional rotation, but the drag may be biased.
Although the teeth are cut with an “involute gear cutter” it is not really a gear either, since it does not mesh with anything.
I managed to scrap 3 parts before producing a useable bushing/clicker wheel. So here is a photo record to help me the next time I do this part.
This is the simple fixture that I use, just a piece of shaft material drilled and tapped at one end, plus a clamp screw, washer, and spacer.
When a brittle material like metal is drilled, the hole is likely to be a little larger than the drill bit. But when drilling a tough material like Delrin, the hole is little smaller than the drill bit.
So when I push the fixturing shaft into the new hole, it is a firm fit.
I next turn a .900 inch diameter (a little smaller than the gear dedendum circle) for a length of .97 inch, just .01 inch shorter than the shank of the finished part.
So far, concentricity of diameters has not been critical.
But the gear OD has to be concentric with the bore. So I re-do the press of the part on the fixture, letting the shaft protrude from the toothed end.
Then I center the fixturing shaft in a 4 jaw chuck.
I can then remove the fixture and ream the bore.
This reamer is 6.4 mm diameter, or .252 inch. Like a drilled hole, the reamed hole is a little smaller than the tool. It is a good running fit to a .250 diameter spindle.
At this point, I measure the bore of the mating spool.
My spool drawing calls for a .4375 inch reamed bore, but the truth is that my Sherline lathe does not have enough low speed torque to make this. So I have to use a boring tool, somewhat less accurate. Also, the spool is anodized, which reduces its bore.