Originally Posted by frank_ster
the only trick that isn't obvious to most people is the two equal cut final passes to get high precision on the diameter. other than that i'm sure david will figure it out!
I typically make the final cut nice and shallow as well, like .002" or .003" for a nice finish.
The soft jaws help avoid marring the machined surface of the piston by the chuck. I like the 4 jaw chuck better. Agreed on deburring any marks left by the chuck.
I'm thinking of cutting thin slices of large diameter PVC tubing to slip around the back side of the piston where it gets chucked. No marring, easier to adjust parallelism, and faster to chuck up. Match the ID of the PVC as close as possible to the OD of the piston diameter to be chucked, then cut the slice so that it will flex in/out to conform to the backside of the piston. That would make it easer to chuck the input piston as well, which has a fillet radius on the back side right where you want to chuck it. You need some type of spacer there anyhow. I used 4 random pieces of 1/8th aluminum the first time. The PVC spacers will be the way to go though.