Post by Deleted on Oct 29, 2008 22:15:49 GMT
Finished the pistons today: nobody told me that PTFE expands once it's been parted off! I say this because I used my usual slip guage method to get the width to fit the piston groove, but when I took the ring to the groove the ring had 'grown' about 8 thou! A whole new method of turning was opening up!
The W & M says to machine the pistons in three separate ops: one to rough turn the length, re-chuck to drill and mount piston rod for concentricity, make a collet, mount piston rod in collet, turn and face the piston to size.
As I'm basically lazy, (and the chatter potential is huge) I decided to make the pistons at one setting, not bothering with rechucking and making collets. If anyone's interested: face off, drill for tap, drill halfway for piston rod interference fit, tap for rod end, turn piston to finished diameter, turn ring groove, part off most of the diameter, insert piston rod and tighten using tailstock chuck, leave piston rod lightly supported in tailstock chuck, continue parting off. Reverse, face to width. Done as shown below.
I made a brass carrier for the piston valve rings, but it was a bit heavy, so used a nice piece of aluminium instead. The cheeks are only one mm thick, but support the thing quite well, and, to my surprise, facilitate some 'adjustment' to the ring size if tightened up! How it will stand up in practice remains to be seen.....
End covers: I'm using 1/8th brass plate hacksawed to a pentagon, and using the linisher to get close to 1 13/16ths. I'll finish it in the lathe aka the suggestions as to finishing copper discs.
What ever happend to the coupling rods.....
JB
The W & M says to machine the pistons in three separate ops: one to rough turn the length, re-chuck to drill and mount piston rod for concentricity, make a collet, mount piston rod in collet, turn and face the piston to size.
As I'm basically lazy, (and the chatter potential is huge) I decided to make the pistons at one setting, not bothering with rechucking and making collets. If anyone's interested: face off, drill for tap, drill halfway for piston rod interference fit, tap for rod end, turn piston to finished diameter, turn ring groove, part off most of the diameter, insert piston rod and tighten using tailstock chuck, leave piston rod lightly supported in tailstock chuck, continue parting off. Reverse, face to width. Done as shown below.
I made a brass carrier for the piston valve rings, but it was a bit heavy, so used a nice piece of aluminium instead. The cheeks are only one mm thick, but support the thing quite well, and, to my surprise, facilitate some 'adjustment' to the ring size if tightened up! How it will stand up in practice remains to be seen.....
End covers: I'm using 1/8th brass plate hacksawed to a pentagon, and using the linisher to get close to 1 13/16ths. I'll finish it in the lathe aka the suggestions as to finishing copper discs.
What ever happend to the coupling rods.....JB
