Sunday, August 23, 2015

Big wheels on a small lathe

No matter how large a lathe you have, sooner or later you will come up with something too bigto turn. When I went to module 0.9 on the clock, I calculated the size of the biggest wheel and found I could swing it (that is, get it on the lathe without colliding with the bed). So I said, let us go ahead and do this thing with module 0.9. The following picture is the 50 tooth gears made so far. None of them are stellar. So we foresee problems ahead.

First thing was to cut the blanks out for the midsize wheels. I did this on the bandsaw. The first thing I did was to cut out masonite-type board slightly smaller than than the gear itself. When I put it on the lathe, it was very obvious that the regular toolpost was not going to reach to the rim and cut it. Impasse. Next morning I started designing a fixture that would move the toolpost -- and realized as I did I already had one, the compound slide. The Taig compound is very flimsy, so I usually don't use it unless I have to cut tapers. So up with the compound and success:

plus I have an extra 25 mm (1") by moving the tool to the outside groove.

So the last problem was to make a new dividing head plate. I did this my usual way, with my PostScript program. I used my optical center punch. Then off to the drill press. Just to make sure everything was centered, I used a fixture.

Then I put the dividing head back together and tried some more 50 tooth blanks.  None of them were stellar either. There is something wrong with the dividing head. But that will wait until the next episode.

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