My.. More replies than I expected!
Zee, Artie, Ron, Nick, Phil, Tel; Thanks a lot for checking in on the thread.
Zee, it's a common machinist's term, pretty sure.
Artie; Just pullin' yer chain, mate.
Ron, Thanks for the tip! I have a small piece of nice beveled edge thick glass around here somewhere, but I've moved things around the shop lately, and can't lay a finger on it. I usually use that, but the real thing would be nice.
Nick, like Tel says, there's a plate that goes on the cylinder. You'll see it down a bit in this post.
Phil;
1) Drill rod, but CRS works just as well.
2) It was just one that I had already made up. Yes, a shorter one would be more rigid. The last cuts have to be pretty shallow with a light duty bar like this one.
3) Yes, hardened and tempered, like if you were making most other kinds of cutting tool.
4) The mic sits right on top of the cross drilled hole when measuring. The hole is a smaller diameter than the pads on a mic, by about half, so it doesn't interfere with measurements.
Another way to do it is to make a gauge from a small rectangular piece of steel. Just cut a slot in the piece of steel to the same depth that the cutter on the boring bar will need to stick out for the final cut. You can judge your other cuts by eye, and when it comes time for the finish cut, use the gauge to set the cutting bit.
5) Oh yeah. I sure would. Use the largest diameter boring bar that is practical.
Tel, you got it!
Here's the piston work;
I started with a kind of over long piece of brass stock for the piston..
Seriously, I don't like cutting working sized pieces of brass off of longer stock, simply because
it's so expensive. By the time I cut a piece long enough for work holding and making the part,
half of it would end up as scrap box material. So, I chucked up a longer piece I had and put the
steady rest on it. Then, when I part it off, the majority of the longer piece will be intact.
This is a mistake. I caught it one second after "just in the nick of time" happened. Got
carried away roughing out. Another piece for the scrap crate. (I'm way beyond scrap
box.)
Everyone does this kind of stuff. Some people keep it to themselves...
Try again, and this time, measure well before I think I'm "about there". Here's the good piston
having a hole reamed through it. Then it's parted off.
Then, cut a piece of 1/8" drill rod and thread the end that will go into the cross head slipper.
Then the piece is parted to length.
I put this picture here mainly so I could mention something about the small straight edge rule
behind the threaded piece. When taking pictures of little bits, and you have your camera in
macro mode, if you put something directly behind the object you want to be in focus it will help
the camera "see" it. Sometimes on a thin piece that has a large background, the camera wants
to focus on something other than the small bit. Putting something right behind it, the camera will
pick up on the contrast and focus on the smaller piece. This is just for auto focus cameras.
Next, the steam chest is milled out. A straight forward milling job, and everything was
located by coordinate.
I milled the piece as shown, and when I got to the last .020" or so in the bottom of the slots
you see here, I milled through first the two longer slots, then one short end, letting the thin
web of the other short end hold the waste piece in place. Then, put a little pressure on the
top of the waste piece with a pencil eraser as I cut the final short side. This helps keep the
piece from pinching the end mill as the last cut is taken, which would cause a ruckus.
Then milled the end of the piece that will form the valve slide rod bore and packing guide, and
drilled and tapped the needed holes. Those M&M's just came out of nowhere.
Milled slots in the valve face plate.
Next I turned my attention to the fasteners needed to attach the steam chest, valve plate,
and cover plate to the cylinder. The print shows studs and nuts. I've made enough of those
for the time being, and since I had some 1/8" stainless hex rod, thought I would use cap screws instead.
This one shot tells what was done, but just in case, it was like this; Turn the hex rod down in
steps to the diameter needed for threading. Thread the end. Pull a little more of the rod
through the chuck, and part off the end of the screw to what looks good to me. Then,
(adjust the parting tool, and,) do it seven more times.
This is what I've got so far.
Here's how the cylinder pieces go together;
The cylinder.
The valve face plate.
The steam chest.
The cover plate.
And everything buttoned down tight.
I'm thinking I might make that cover plate again. Not sure yet. It was cut from a stock
piece of 1" wide brass flat, and the edges are rounded over a little. It's also a different kind
of brass than the rest of the cylinder parts, and has a slightly off color.
That's it for now.
Happy Thanksgiving.
Dean