Tuesday, July 28, 2015

Life at module 0.9

In the last episode, we nade some lantern pinions. Measurement revealed that they were actually module 0.9. So this is really a  blessing. Since I am making my own cutters, the larger module will be easier to work with. So I am now embarking on the process of cutting the wheels. The first problem is to make the cutter.  I use Dremel 3mm tool shanks from expended Dremel tool cutters. Cheap, and they are good steel. they can be hardened and tempered. I am making a fly cutter, a one-point cutting tool.

Now a fly cutter does not actually cut teeth. What it does is cut the space between teeth. A clock tooth is supposed to have a cycloidal profile. This is the profile generated by a circle rolling on another circle. Yuk. However, this is approximated by a straight cut with a "rounded  over" circular radius at the tip. The radius is something like 1.7 mm at module 0.9.

So as a first task I made a button gauge.

I turned down a piece of steel to the proper radius, say 1.7 mm. I am too tired to go consult my notes in the shop. I drilled two holes the proper distance apart. This was done on the mill, you could never hit it by eye. The button gauge will be used see if I am on target with the radius. There is the problem of depth of cut, but if I overdo this I can always grind it off. Off to the mill.

Here we have an expended Dremel shaft put into a homemade fixture, a piece of square stock with a setscrew to hold it in place. The fixture is clamped in the mill vise.

I have available 3mm, 2mm, and 1mm. end mills. These are diameters. Hmm. If I were to cut 1.7 radius I would need a 3.4 mm cutter. Unicorn. Uncomfortable. But the 3mm guy will go 1.5 mm aand for now that will do. It is quite difficult to center up the cutter. But above you see it taking shape. So I did this. Now we heat it up red hot and quench. This will harden the steel.

I use my handy furnace and water-quench, and then temper, a difficult job on a piece smaller than your little fingernail.

Having done this, we take a test cut on a leftover blank we happen to have. The diameter is completly off, we just want to see if the cutter works at all.

So I mount this random blank on the dividing head and cut a few teeth. The diameter is wacky. But it does work -- i.e. it cuts teeth. Spacing all wrong of course.

Next step is to turn up a proper blank on the lathe. I cut them out on the bandsaw. The scrollsaw would be better, but it melts the plastic so the bandsaw wins.

Now we can cut teeth properly. I did a whole bunch of them. There are so many errors you can make. You can forget to tighten the dividing head, for instance. This will chew the blank. You can forget to loosen the dividing head, which will mean slippage in the gear train. Maybe I should loctite the worm. But I don't want to do this yet.

Anyway, at the end of several days work,  I came up with some wheels.

The leftmost wheel is complete chowder, as Tom Lipton would say. As we go left to right, we see gradual improvement, as I correct my mistakes, so the rightmost wheel is almost usable. But there are two problems. The tooth profile is off. Also the spacing is irregular. The tooth widths vary. This is a problem with my homemade dividing plate. In the next episode we del with these problems.

Sunday, July 12, 2015

The saga of the lantern pinions

In a clock, the gears that convert the movement of the pendulum to the movement of the hands are of two types. If the gear  has 12 teeth or less it is called a pinion. If it has more than that, it is called a wheel. The Isaacs clock has 8 toothed gears for the pinions and other numbers for the wheels. Pinions are small fiddly things, about 6mm diameter. That's about 1/4" for the metrically challenged. Now there are several ways of doing pinions. First is to buy a commercial pinion cutter. Messrs. Thornton in England will sell you one, at what I consider an exorbitant price, 40 quid or about $80. Second, make tour own pinion cutter. I am really challenged here, because my mill is a real micro. The largest collet it will take is 3.2 mm (1/8") so the  7mm diameter of the hole in Messrs. Thornton's cutters is far too big for my tiny Proxxon mill. Second, make your own cutter. I looked a lot into this and they are quite a complex problem -- again because I have such a tiny mill. I will deal with this some other day. I can do it, I think, but I will have to rescale a lot of things.

The third way is to make lantern pinions and this is what I did. Essentially a lantern pinion is a very small hamster cage. It is two circles for the side of the cage, and 8 bars to the cage. Eight bars work out conveniently to 45 degrees at a side.

So I made up a wheel divided into 45 degree increments. A production,  but possible. I then used my aformentioned Dremel tool holder to drill the 8 holes. Simple, eh? Not really. First I had to make a mandrel, a shaft that fits into my "crocodile," the ER-16 collet on my Taig. I threaded it US 4-40 because that is the smallest tap and die set I own, about 2.4 mm. Then I had to make a special nut to fit the 4-40 thread and not interfere with the boring of the holes. A standard 4-40 nut is too big. The diameter of the hamster cage is 6.1 mm at module 0.6.

So now we turn up a bunch of hamster cage circles to the proper diameter, which is about 12mm. This can be done en masse, four sides at once. Then I laboriously cut up some music wire into cage bars. Regardless of its name, music wire has nothing to do with music, and worse, it is often called piano wire, although it has little or nothing to do with pianos.

The first result is shown above. It is a valid lantern pinion. It is sitting on top of a ski wax container. I use the ski wax on bandsaw blades and it really helps.

Now I made up an index stop out of an old saw blade and a broken Dremel mini-drill. I have lots of those, they are are very easy to break. The ones I am using are about 0.7 mm but unfortunately the wire is 0,77 mm.
The index stop is saw blade attached to a magnet., super-glued to the saw blade. I works.

And fortunately, looking through my supplies, I found a wire (from Michael's) same gauge as the music wire, slightly less stiff, and far less expensive. And much more obtainable. I have bought out Lowe's supply.

So here is the final mise en scene (forgive the lack of a grave accent). These are the tools I used to make 9 lantern pinions. I should only need 7, but better safe than sorry. There are pliers, of course. Then is my Archimedes drill. This has a piece of music wire in it, which is used as a drill/reamer to bring the holes in the cages to final size. It was quite a feat to grind that thing properly so that it would actually drill.

 There is an 8mm wrench that belongs to the mill. I use it to cinch up the pin vise, the invaluable object on the right, which holds the wire while you get it through the holes. Sitting in the pin vise is the last of the hamster cages.

When it was all over I measured the diameter of the pins in the cage. It was supposed to be 6.11 mm and came out to 7.7mm. Ouch! This is a major blunder. A real Bozo, as Tom Lipton would say. However I think it is a blessing disguised as a blunder. I worked out what the module actually is, and is 0.9 instead of 0.6. I think this module will be much easier to work with. Of course I will be into a redesign of the clock because the spacings will be different from the plans. But since I can calculate all of this, the redesign will not be too bad a deal. I can still swing the biggest wheel on the Taig. Stay tuned.

Sunday, July 5, 2015

A bookcase for the shop

It ocurred to me that it would be an excellent idea to have a bookcase in the shop. I have some books to which I often refer. Notice that I did not end a sentence with a preposition. Notice that it sounds clumsy to modern ears. Anyway,  I was inspired by Paul Seller's work. If you search for him, you will find everything. But Paul's YouTube videos deal with hand tools only. Just my ticket. So I went to Home Depot  (by accident, because I was looking for somehing else) and found a nice piece of cedar, sold as fencing and very cheap. About $1.69 as I recall. I decided I would use it as a bookcase and as a box for my dividing head. I lopped off what I needed for the case and that left me with some cedar. I planed it off, an excellent cardio exercise. So I want a dovetail case.

 I realized ex post facto that I should have done this backwards. You see above I am cutting pins in the uprights, Should have cut the tails instead. Simply a matter of appearance, joint is the same. One of Mr Seller's most interesting ideas is that of the "knife wall" and it did manage that correctly. When it came to putting it together it was another thing, I erred. Still, it came out all right. Not perfect. But 'twill suffice. Hand tools only for this thing.

So now it holds my essential references, and I am happy with that.

Back to the clock,  but that was a pleasant interlude.Coming next: making lantern pinions for the clock,