Wednesday, April 29, 2015

The romantic tale: mill meets dividing head.

In this episode, we put the dividing head together. Some fancy milling was involved getting the worm shaft support to match with the tilted arm, but it got done. I spring-loaded the sector arms and they work fine. There is a collar that is pressed on to the crank arm, held down with a setscrew..

You will see that I have not cut off the worm shaft yet. No matter, will do that later. The thing to do is now to bolt the thing to the mill and see if it fits. Cecil, meet Ms. Head. Now the question is, does it fit? Is this true love?

 Well, pretty much. There is enough clearance, the plates do not scrape on the table. But as in all romances, there are some rough spots. We can see this in the following picture. I have installed a fly-cutter in the mill to illustrate the problem: the Y-axis travel is insufficient. I could cut the 30-tooth gears with this setup, the diameter is but 30 mm or so. But the bigger gears will give me a problem.  The biggest gear in this clock is 90 mm diameter, if I remember correctly. I cannot move the Y axis back any further. I will have to think about this, so stay tuned for more romantic tales.

But I am quite pleased. I have actually built a dividing head that fits my mill.

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.

Computer table finale

This is the finale on the computer table. After a few coats of linseed oil, the frame is complete.

The house came with a couple of boards. One of them, cut in half  (also oiled) gave me a nice top. Beaacuse of all the knots, it was a bear to plane.

And finally we put the thing in place.

It is an enormous relief to have a decent computer table. I am rid of the sawhorse and board arrangement I have had ever since I moved to Chalupy! It was at best uncomfortable. I am very happy with my new table.

Tuesday, April 7, 2015

A table interlude

For the last ten years my computer table was an old door set up on sawhorses purchased from Lowe's in Wasilla. When I got here I set up the same old sawhorses with a top I had made for some side tables in Juneau. It was bugging me to death because it was too narrow, so it is time to make something better, thereby interrupting my dividing head work. Hence, a woodworking interlude.First step, go to Lowe's and buy some cheap 2x4. Next step is to plane the stuff.

This was an ordeal. The wood is gnarly. Well, at $2.67 for a 2x4 you can't expect much. I tapered the legs on the bandsaw,  then planed them. Even so I used every plane in my arsenal. Now, for interest, I decided to arch the crosspieces. I rigged some trammel points. The arc I wanted turned out to be a meter ten!  Here are the tramel points in action. I then cut the arches out on the bandsaw. The trammel is a total inprovisation. A meter plus is a long radius indeed. I am glad my woodworking bench is so long.

Next step: the bandsaw. Cut the arches out. My usual hate of power tools was abrogated in the interests of getting this thing done in a non-geological time frame. The results are rather ugly:

These are the pieces I cut out on the bandsaw, freehand.  They still need some manual work, so I broke out the spokeshaves.

Now we look a little better.  Here's an example. I decided to use my usual saddle joint at the ends, so I cut, by hand, the mortise and tenon. I had a lot of trouble with this. Out of practice, and wrong ryobi saw.Still, it looks OK and that is my main concern.

 So, some tediun later, we have something that looks approximately like a table frame.
 I already have the top cut out from a board that came with the house. I hate it, but 'twill do, 'twill suffice. Here's another view.

I am not proud of the saddle joints, but I am not about to redo them. Also I do not like the taper. What I don't like is the top of the joint. This is a measurement error on my part. In excuse, I did it in inches! It should be straight, at right angles to the top. Too bad. I could fix it, but I have been on this thing for a whole week, and I am getting tired of it. This, like the dividing head, is composed and not designed.

After the first coat of linseed oil this morning, the thing actually looks pretty good.

Next, the top goes on. I regard this as a temporary top just to get me out from the sawhorses. Now I can get back to the dividing head.