The .444 Magnum Oscillating Engine

I got tired of cutting clock wheeels and badly needed a vactaion sooo....

One of the first projects the beginning "model Engineer" does is an oscillating engine. These are very simple engines, where the cylinder oscillates back and forth to expose the intake and exhaust ports. A complete video of a build of an "Ossie" (as these things are called) engine will be found on Emma Ritson's channel on YouTube, if you want  to see a blow-by-blow description.

What had been holding me up was the lack of suitable material to build the cylinder.  But I found, still at Chalupy (which has probably burned to the ground by now, there is  huge forest fire there) an expended .444 Marlin cartridge  case. This is cylindrical, no necking at all, so it seemed like a possible candidate. A test with calipers yields 10.47 mm and the drawings call for 10mm. Close enough. In this build I have followed Mr Stan Bray's book, "Simple Steam Engines" and I must say both the words and the music (drawings and instructions) leave something to be desired.

Anyway, while I was at it I built a finger plate. This is a gadget to hold things down while you drill or otherwise machine them. It is a piece of aluminum with holes drilled in them. I got the idea from Clickspring's Channel on YouTube. It has a 45 deg  groove in it, which I did by tilting the block 45 deg in the vise and using an end mill.

So, a bit of Aluminum later, we have a finger block.

Next thing to so is to mark put the port face, which will be soldered to the cylinder. [In retrospect, I should have not done this. I should have bored out the cylinder and made the piston fit it. I also should have drilled the pivot, but not the port hole. I plead just following directions in the book.]
You see the finger plate in action.

So next we solder the cylinder to the port block. This went very well.

I turned a rod out of a Dremel tool shank. These need to be turned down to 3mm and threaded. They are around 3.2 mm so it is delicate. The only 3mm tap and die set I have happens to be M3x0.5 so that's what it got. Both ends. This is the pivot shaft; the pivot will rock about this.

Next job is the frame. I took some pains to line it up. It is very fortunate that Ossies are very forgiving.

Then I drilled the port hole intake and exhaust ports. They are tiny, about 1.5 mm. Then I made some more little fiddly parts (go see Emma's video) And  then I discovered the holes would not line up. In fact the piston would not go in all the way. I soldered the original port block hole up.




So I had to bore out the cylinder. Of course. It is an expended cartridge. Who knows what egg-shaped sections lurk in the heart of an expended cartridge? Had I done this in the first place, I would have saved a lot of time. In a limp excuse, brass is unobtainium in Alaska, except for cartridger, expended of course. The problem was indicating it. Because the port block has already been soldered I canonly indicate 2/3 of the diameter. I put up the 4-jaw chuck and did what I could.

So I turned a piston and voila, Marlon the .444 Magnum repurposed.

Still not right. Of course. The original called for a much thicker port block than I have. The piston was too short and the port holes would not line up. So I turned a new piston. Here is Version 0.2.

BTW Cecil B. De Mille is excellent for spacing accurately placed holes.

 Today I drilled the hole in the port block. It seems to work.

So here we are. I will return, I hope.

Dividing head contiued

The last post (sorry for the delay)  showed the head mounted on the mill. This immediately showed a number of faults in the construction. One obvious one is that the slots in the head weren't long enough for the bigger gears in this clock. So take the head apart, and back to the mill. Make those slots longer. First to port...

and then to starboard.

So now we have the slots to proper size. A far worse problem was that the bearing of the gear wobbled.  This was major surgery. I pressed the gear off the shaft. I turned it down to 5mm, because I just so happen to have an M5x0.80 tap and die. Thread the shaft in the lathe, make up a corresponding nut. Ideally it would be knurled, but I don't have knurling tool. So I cut longitudinal grooves in the nut, and it worked very well. You can see the nut in the picture below. Middle of the picture. If it is tightened down, the gear will not move. I suppose the worm slips on its shaft. Urk. But it sure squares up the gear.

Another view from the business end of the device, my Proxxon spindle knock-off.
In practice the gear  is held on a fixture which I turned up. It has a 3.2 mm spindle, i.e 1/8" spindle. I had to turn up a similar fixture to hold  the fly cutter I propose to use. I think it may have made its appearance in a previous post. It fits the 3mm Proxxon collet. 

Well. I can't put this off any longer. Some previous experiments showed me that my fly-cutter was way off. But there are many variables. So let's try an official gear blank. I have tried power tools but they melt the plastic  I am using. So back to the Jeweler's saw. This is a piece of plastic about 3mm thick frome Home Depot at the stunning cost of $3. I doubt that anywhere in Alaska could I find the "compo brass" called out for this clock.

Having  roughed out the blanks with a saw, they are turned to the proper diameter on the lathe.

I am using my new ER-16 collet set, which I call the crocodiles, because they really, really grip. Goodbye, wimpy Taig collets. The new Taigs are bored out to accept ER-16 collets. OK, so we set this stuff up on the mill and proceed to cut gears.

Hah!  Not so simple a job as you might think. You have to (a) unlock the spindle (b) rotate the head the proper amount,  (c) lock everything down, (d) move the Y axis of the mill in 1.74 mm to cut the tooth. If you do not execute these steps in exactly that order, disaster is sure to follow. I am so glad I am using el cheapo plastic instead of brass! It is particularly important to remember when to lock and unlock the head.

My gears so far are a disaster. But we are now down to the profile of the fly-cutter. Today I made a gadget to help me judge that. But that's another post. Patience is the prime virtue of clockmaking. Just for fun I point out that the module of these gears is called out to be 0.6, which gives you a rough idea of the scale of this thing. Half a millimeter per tooth!  Acually pi times that. It is a small clock indeed. So small errors are hard to avoid.

Stay tuned for further adventures in gear-cutting.

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.