This week I started back on the Pennsy, with the next major subassembly being the Cylinder Cocks. They sound so easy, but there's quite a bit of mechanism to these since they have linkages that allow you to open and close the cocks from the cab.
Chapter 19.1 – Cock BodiesThe first part of the Cylinder Cock assembly is the cock bodies themselves. They are made out of bronze. I used 932 bearing bronze, which machines really nicely.
The smallest bronze I purchased was 3/8” nominal – which is really more like 0.412” I had to use a 27/64” collet to hold it. So first I turned it down to the specified 0.200” for the main cock body, then turned down the last 1/8” for 8-36 threads.
Then I drilled the main drain hole. This had to be deep enough to get close to the bottom of the drain cock, but not break through. I had to trust my math on this one.
The last step on the lathe was to narrow down the ‘bottom’ part of the cylinder cock and make a little taper, then cut it off from the parent stock.
I made four of these. The picture on the left shows where we’re headed. Still have two holes to drill crossways. The big one goes all the way through and is where the actual on/off valve will go. The lower smaller hole only goes in halfway to connect to the central drain hole.
To get these cross holes in the correct position, I fitted all four of the cock bodies in place on the cylinders. It was hard to get these in tight since there was nothing to grip on, and I didn’t want to use anything that would mar them. With them in position, I tagged them with a 1/16” number punch so that I could get them all back in the same spot. To mark the location for the holes, I colored an area with a black permanent marker, then used a small flat file to gently rub along the front leaving a very small mark at the correct location.
To drill these holes I followed Kozo’s directions and made a little jig to hold the cylinder cock bodies. There’s a ~0.200” hole in the side where you slide the cock body into, two holes on top for the locations of the two cross holes, and a set screw on the side to hold the cock in place. My additions to this little jig were to use a small spring behind the cock body so it would push out against my stop that I would position exactly 1/8” from the side of the jig. This made positioning the cock body much easier!
Here’s what the jig looks like in use. You can’t see the spring, but it’s in there behind the cock. The two 1/8” chunks of aluminum being held by the clamp are used to set the position of the top of the cock. I used tweezers to rotate the cock till I could see the witness mark and would adjust that till it was as close to centered on the holes as I could get it, then tighten down the set screw.
And now, drill the two holes. For the larger hole (the one I’m drilling in this picture) Kozo specifies to ream it to 0.100”. My problem with that is it’s hard to come by 0.100” rod in the states. I chose to make it 0.0938” (3/32”) which is readily available, and pretty close to 0.100”. So I drilled the holes with a #43 drill. The other hole was drilled with #56 with the depth CAREFULLY controlled since it only needed to go halfway through to meet the other central hole in the cock body.
After I did that for all the cocks, I went back through, lined them each up again, and reamed the large hole to 3/32”.
And here’s how the cock bodies look now:
The next part up is the cock plugs that go through the cock bodies and actually open and close the cocks.
Thanks for looking in on me!
Kim