17 years ago
lathe. I found replacement gears at $90 each (plus shipping) and
decided to make my own. I thought that I could hob them, but measuring
the gears revealed that I'd need a hob with 5.38 tpi (4.72 mm pitch).
Ok, maybe I could make them the hard way (one tooth at a time on the
mill). Well, I did and they work just fine!
Of course, it was a rather drawn out process. To make the gears I needed:
1. a blank. I chose aluminum and I cast one and needed:
- a pattern
2. a cutter. I ground down a plain milling cutter, for which I needed
- a fixture to hold my Dremel in the lathe tool post
3. an indexer for the mill. I bought one, but needed to make:
- an adapter plate to hold it on the mill, and
- a spanner to tighten the index plate
This was the worst case of "making a tool to make a tool" that I have had.
When I ground the cutter on the lathe, I ground off the relief that the
original cutter had. I thought that *maybe* I could get away with none,
since I was using an aluminum blank. WRONG! I got nowhere when I tried
using it. I ground in some relief (by hand - it wasn't too bad). What
a difference - I cut the teeth in one pass!! .130 d-o-c! My first
tries involved a slitting cut as the first step, but I really didn't
need to do that.
I didn't do such a great job grinding the cutter and got teeth that were
not quite involute. I.e., they were straight. This resulted in all the
meshing contact to be at the ends of the teeth. It worked, but wasn't
really right. So I hand filed the ends (36 teeth x 2 sides x 2 gears)
and got them "close enough".
Now, I'm sure that it is obvious that all this did not result in what
you'd call a "precision" job. But the gears work and are just as quiet
as the ones that I broke. And the QC box is not really a very demanding
situation: low speed and small forces, so I'm comfortable with them.