Sunday, September 27, 2015

Termination dust, 2015

I see I have already posted on this phenomenon before, because I have created a label for "termination dust." In order to save you the trouble of searching this blog for that label, I will repeat myself, as Walt Whitman did indeed say.

In the old days, when a prospector's claim ran out, he would start getting dust instead of nuggets in his pan (or whatever system he was using), and this was termination dust. Claim done. So nature gives us a similar signal" summer done.

Unfortunately my zoom feature has ceased. I fear my camera has therefore deceased too. Well, out on the back porch, we can just see dawn, and snow dust on the Chugach range. But there it is. The Fireweed has folded up. The birches turn yellow. Winter is upon us. Part of the fun of living in Alaska. Here in suburbia I can't go out and cut firewood. But we must accept change. The year wheels.

Sunday, September 6, 2015

Dividing head woes

Things have been very awry. My clock wheels are in trouble. Fortunately they are acrylic, or I would be out a fortune. Problem is that while some of the teeth look fine, others have flat tops. After pondering this one for a while I finally came to the conclusion that the dividing head is running out. This means it isn't centered. It is wobbling. So let's check.

Observe my new elegant mini-dial indicator holder. It will hold both my Imperial supersensitive indicator (shown above) and a conventional DTI. It is being used to record the runout (wobble) on the wheel, which is is on a mandrel (shaft) held in a collet. These are my wonderful ER collets. They have essentially zero wobble.
 'Nother shot same thing, same results. Runout about .002" or about 4 "cents" (.04mm). Uh-oh. The wheel is quite acceptable for clockwork. Time to check the runout on the shaft of the dividing head. This is quite a production. The dividing head is mounted on the mill. This, except for the base, is made of non-ferrous metal, and the indicator base will not adhere. So I had left the vise on the mill. In it I clamped a piece of angle iron, aand the dial indicator will adhere to that!  So by now I had acquired a metric dial indicator, and checked the runout again. Horrors. A whole millimeter!
The runout is all in the shaft of the dividing head.

Then  I took the dividing head apart and checked its shaft. It needed no dail indicator to show it was bent. So I made a new one. I used my steady rest to hold things still. Here I am, parting offf the result. I claim a new method of parting off. I use my Dremel tool holder, one of the very fragile  cutoff wheels, and spin the lathe one way and the work i t'other. Got a nice clean part, and a very narrow kerf.

So the next thing was to do something about this. It is a very small dividing head, so my next idea was to add a new outboard support.  It is an aluminum block. Here it is under construction.

The results on divde head 2.0 are not encouraging. I measure the runout  on the new spindle:

It still comes to 30 cents. While better than a whole dollar it is not very good. Impasse. While I am figuring out what do do about this, I added a new feature to Cecil B. de Mille. Behold my Z-axis Digital Readout.

Just a super-cheap digital plastic caliper, a bit of angle aluminum, and some drill and tap, and now I know where my Z-axis is. Of course I can always use the dials. But the Count himself (on Sesame Street) would get confused  by the number of turns you made. And one turn off is a whole millimeter off. Worthwhile addition.