Pistons
I am back at it, finally. The Thanksgiving holiday was filled with wallpaper removal and ressurecting a boarded up and plastered over laundry chute. The wife is happy, and I did the near impossible, loosing weight over the holiday, despite eating everything in sight.
I tweaked the drawing a little, adding .1" to the piston in various places above the wrist pin, and shrunk the connecting rod by .1". I also ordered a piece of A2 to make a ring groove cutter, and picked up a reduced shank 9/16 drill bit. Minor tooling additions, but they made a big difference.
I start with two pieces of 2024 about 1-3/4". It is a bit of a waste for a part just under 3/4" but there is no substitute for having a decent piece of stock to grip on, and a little clearance from the chuck jaws helps a lot too. The stock is squared up in the 3jaw with a dial indicator and gentle taps of a plastic hammer, then faced off to make a measuring datum and drilled .662 deep with a 9/16 drill.
Now the fun really begins. I move the drilled and faced blanks over to the 5C spindex, which has had a little attention paid to its lateral play since the last attempt. It was rather ,so it was greased up, and tightened up, best as I could. The wrist pin hole is drilled and reamed under power, .351" from the face. Then we move up to .478 and drill the 16 .0625" oil drain holes in 140 degree arcs between the wrist pins. I used a parabolic flute drill, and after bringing the drill bit to just spot itself, it was drilled under power from the quill. These holes just broke into the shoulder of the earlier 9/16 drill hole. This worked wonderfully, and the power downfeed probably saved me a drill bit or two because I couldnt get impatient.
Back at the lathe we do the same centering trick with the plastic mallet and dial indicator, helped a bit by keeping the written bar identification under the same #1 chuck jaw each time, we sucessfully recentered the part in the 3 jaw with under .001 runout. Then we turned a minimal amount of skin of the 1" bar to the .948 diameter.
The piece of A2 tool steel was earlier machined down to .037" width and hardened. I carefully aligned it to center and optically zero'ed it to the earlier faced off bottom of the piston. The carriage was moved so that the bottom side of the tool was bisecting the oil holes and the oil ring groove was cut .045 deep. It cut like butter and I couldnt have been happier.
No further drama ensued as I stepped up another .070 to cut the compression ring groove .039 deep. This was a great relief as my earlier hand ground form tools did not leave the ring groove square and wandered around a bit. These grooves came out quite clean and square. Cleaning up the work from this side of the piston, we bored the bottom interior .23" to .886" id.
This piston has a 15 degree crown, and previously I attempted to part it off only to shatter a toolbit and give up, hacking it off semi flat. This time I centered the work with the 4 jaw and using the crosslide set to 15 degrees, I ran the lathe in reverse and trimmed the part from the backside. This left me with only one problem, that I could not measure the overall length of the part with the other side firmly in the chuck. I scribed a line .611" from the face where the crown starts, then I used a small measuring pocket microscope to determine how much to move the carriage. I can happily say that one part was only .002 too short, and the other .006. Close enough for that measurement in my book.
Now I have two happy pistons.
Identical enough in every respect, I am pleased and quite relieved it is all over. I will likely take a ball mill to the inside later, when I set the rotary table up, but that falls under the "pretty" heading more so then a functional one.
As always, feel free to chime in if I am doing something the wrong or hard way, or especially if I am ignoring the obvious. I am self taught from a lot of reading, but not a lot of doing. I have learned a lot on this forum and others, so if you see a teaching moment, dive right in.
Next up? These pistons look a little naked, so I will probably make the jigs to heat treat and skim the rings. I likely wont do a write up on the wrist pins themselves, but its getting time to finalize the connecting rod drawings and they will likely be the next major pieces.
