Monday, March 30, 2015

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.

Monday, March 23, 2015

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.

Wednesday, March 18, 2015

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!

Sunday, March 8, 2015

A pipe tool and a pantograph

A strange mixture of topics. But bear with me. I got so exicted about using the graver on the Taig that I decided to make something useful on it. The result is a pipe tool. This is the thing us pipe smokers use to tamp down the pipe, clean out the bore, and scrape out the pipe bowl.

The handle was turned on the Taig out of Aluminum. Freehand, with the graver. I am not yet in the brass-turning league, I am working my way up to it. The wire stem cleaner is "music wire" from Lowe's. It says "easily bent for school projects." Hah! Easily bent  by Superman, yes. I had to anneal it to forge the loop. The blade is an ex-hacksaw blade ground to shape and moderately sharpened. There is a slot milled in it, and a brass rivet to hold it all together. It works like a charm. Note the taper at the end of the handle; all by hand. It acts as the tamper. Altogether an extension of the Taig lathe.

The above pic will give you and idea of scale.

So the next thing for this week is that I got all exited about Stefan Gottteswinter's YouTube channel (q.g.) because he has a marvellous precision engraving machine. It is based on the pantograph principle. So what is a panotgraph? It is a device that allows you to reduce, or expand,  a basic pattern in a given ratio. If you are trying to make something very small, it is an advantage to make it twice (or more) times larger and then reduce it via pantograph. So what is a pantograph?

A simple paralleogram. The corners can all pivot. Across the bottom bar are a row of holes,   into which I stick a Sharpie. The midpoint gives me a 2:1 redusction. 1/3 of the way across gives me 3:1. To the right of the midpoint, I get magnification. Not too interested in that.

This is a crude mockup. I am using Sharpies in the holes and tracing the image of a crude letter O on the paper; I did the O freehand. The pin next to the big wood O is the tracer end. The whole thing is a flimsy contraption, built in a few hours, but I got the principle of the thing down with it.

Next thing to do is to rebuild this thing out of metal and adapt it to take a Dremel tool. Then I can do some serious stuff. Stay tuned.