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.

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.

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.

Ividing head saga, part 3

In our last episode we had gotten rid of the plastic stuff. Now it is time to do something more substantial.The first thing to do is to bolt a piece of steel onto the angle iron. You have seen another view of this before. There is a plastic spacer between the gear and the shaft. Now we have to make an upright to support the worm gear. There it is at the bottom of the picture..

But wait. The gear will not clear the shaft. So we have to mill out a 4mm pocket for the shaft. In steel and with a tiny mill (Cecil) this is an ordeal -- the biggest end mill is 3 mm and the pocket is maybe 30 mm. wide at the bottom. But the shape does not matter in the least, and there is less milling if you make it approximately circular. So there it is cut out. Now we have to attach it to the angle iron.

So to do this I had to drill and tap two holes in the angle iron. Thing about small stuff like this is that it vibrates like a reed, and bends over with drill pressure. So you have to support it. I used one of my micromachinist's jacks.

I made these machinist's jacks some time ago. I have two of them, and they are indispensable. A useful project for an apprentice. The paper underneath keeps the jack from slipping. Once you have the holes drilled, tapping is simple. Now we spot in the holes for bolts and screw in the worm support shaft. Voila (or is that voici?):

Now I have to drill a hole at an angle for the worm shaft. The angle has to be quite exact. Too shallow, the worm will miss the gear. Too deep, it will jam. So I am thinking about this one now. Yes, I know. If I had designed it in CAD all would be easy. But just as in music, some people can only play by the notes and others can improvise. Just look at Johann Sebastian Bach. In his day, he was famed as an improviser, and people came from afar to hear him play. Nowadays, everyone plays him by the notes. I think there is a moral there. I am slowly learning CAD, but after decades doing software, I am enjoying improvisation. And there is only one critical thing in the whole project: worm and gear. That is already done for me by the kind CNC people who designed the printer or whatever gadget I salvaged it from.

Dividing head, part 2

In the last post we saw the dividing head in its proto form. As near as I could reconstruct it, that is. But it is very flimsy, even though I intend to use it to cut clock wheels (gears) in plastic. So it is time for an upgrade to stiffer stuff.

The first step was to substitute the flimsy plastic for something a little more solid, like angle iron.

As you can see I have some angle iron -- actually, a piece off an old bedstead I found cast off long ago. I milled the outside as best I could, and I say that because it vibrates llike a tuning fork. I should have used a machininist's jack to damp out the vibes, but I forgot I had made one. The inside of the angle iron has a bar clamped to it. This allowed me to mark out and drill holes for screws to secure the bar to the angle iron. The result is the new improved mockup.

Now we have to put up a vertical bar to hold up the worm. I have that bar milled out, but you will have to wait, because this is the original Topsy. She just growed.
Of course, angle iron is neither square nor uniform, even though I milled the outside edges. It was very clear the worm-holding bar was way off vertical, a whole millimiter. So I spent some time milling out the place where the new bar will go.

 

 

This was quite successful. I had to take off a full millimeter to get it flat.
Next step: square up the bar without moving anything. Then we will worry about the base, and if push comes to shove we will use shims to level it.

In retrospect, if  I had a casting why that would be the way to go. But I have no casting facilities. But so far this has been very enjoyable. Stay, as they say, tuned.

Genesis of a Dividing Head

One of the oldest problems in the world is dividing a circle into equal parts, like cutting a pie into exactly equal parts. We face this problem every time we cut a cake or pie -- how do we give everyone equal portions?  Well, I am trying to build a clock. The Isaacs clock, published long ago in Model Engineer magazine.A beginner's clock, to be sure. To do that I have to build gears. To do that I have to divide a circle into equal parts, corresponding to the number of teeth on the gear. I have a series in this blog (label "divider") on how I did it on the Taig. I built divider plates. Trouble  is, one of the gears on the Isaacs clock has 100-plus teeth. The radius required for a divider plate with that many holes in it is much too big to swing on the tiny Taig. I have learned since that there is a way around that, thanks to Tom Lipton. But at the time I hadn't watched his video.

So while I was still at Chalupy, and half my stuff was packed up, I had an idea. Every time I find a discarded printer, I take it apart. It is a treasure trove of supplies. Ground rod, plastic gears, racks, pinions, motors, name it. So I found a worm and gear of the same module (n.b. for techies, module is the reciprocal of diametral pitch, but expressed in millimeters). So I set out to build myself a dividing head. -- a gadget that will solve the cake-cutting problem very exactly.

This is a project I am making up as I go along. I regret that I seem to have lost the pictures I took at the time. I will attempt to reconstruct the process.

Above are the basic ingredients. The screwlike thing in the middle is called a worm. It is in fact a screw, rather coarse-pitch. It is on a shaft and bearing. The shaft is a piece of brass welding rod, about 3mm diameter.  Bearing is simply a square bar with a hole in the middle. Below is the gear. It happens to have 72 teeth. The gear will be pressed on to the shaft. The right end of the shaft is turned smooth. The left end is my best attempt to duplicate the Proxxon (Cecil B. de Mill) spindle, complete with collet closer. A major turning project which I did here in Anchorage. Then I can use Proxxon collets to hold the proto-gear that I wish to cut.
Now let us assemble the thing. I will cut gears  on Cecil. I have much more precise control on the speeds and movements of the mill table.

This is a real lashup which I will remedy. I hope. The clear plastic is a frame. You see the worm meshing with the gear. Now, an interesting property of worm-and-gear is thatevery time the worm turns exactly one revolution the gear advances one tooth. If we had to cut a 72-tooth gear, we would turn the shaft one turn, cut, turn one more rev, cut ... rinse and repeat. But if we wanted fewer teeth then we would have to turn more than one rev; if we want more teeth we have to turn less than one rev. We do this by using dividing plates. I have also made these things, but that will have to wait for another episode.

A commerical dividing head is quite expensive,and much bigger than my entire mill. No hope there. Proxxon builds a rotary table but very expensive. So stay tuned. This may or may not work!