Wednesday, April 22, 2015

Dividing head coninued

It is unprecedented for me to post twice in an evening, but the Computer table needed a finale. So I finale-d it.

So we are back to the dividing head. The critical part of this is getting the angles right, so that the gears will mesh.

My original idea was to make the support post vertical. Then I had to measure the angle at which the shaft hole would be drilled. This was very difficult. The thing is very small and really there are no reference surfaces.

 I resorted to my surface plate -- the flattest thing in this house, and possibly in Anchorage -- to measure the appropriate positions of shaft and angle. I did the best I could. Alas, I was a whole millimeter off. I fixed this by a slight tilt of the support bracket. This still leaves me with plenty of clearance for the plates.

While I was at it I decided to add a right-side support. This is to keep the worm from going forward, instead of turning the gear. I clamped it up and was able to drill the holes -- but in the wrong places! I had drilled and tapped the hole for the worm end in the wrong place :((.  I rescued this  with a plain old 10-32 screw. I can adjust this screw to compensate for the "endshake" (as we clockmakers say) in the worm. It is unsightly but it works.

 The next thing to do was to machine a spacer, which keeps the dividing plates away from the support arm. This was a nice piece of milling, because the support arm is angled at a very arbitrary angle -- in fact, the angle which allows the worm to engage the gear. I did not get a photograph of this process; too tricky. The spacer, the support, and the backer for the plate are J-B Welded together. Hope it holds. So on goes the plate and the sector arms:

 The sector arms must be locked in place once you have determined the spacing of holes. This depends on the number of teeth you are going to cut. Simple, I said. Just use a couple setscrews. Yes, but the setscrews push the sector arms apart! Aargh! I should learn General Relativity instead of this machine shop biz. However, a spring load on the sector arms should do it. So I found a suitable spring (I hope) in my odds and ends bag, and now I have to machine a suitable spring-hold-downer. This is a job for the Taig:

 I have a piece of scrap in the Taig chuck; I am machining the thing to two diameters, one to fit the crank and one to push down on the spring. I will use a setscrew to hold this thing down on the shaft, maybe a spot of Loctite, too. I have cross-drilled the thing,. Tomorrow, tap it, file a flat on the shaft. There are lots of things to be done yet, but I have made progress. Sufficient unto the day is the evil thereof.

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