Machining piston height

[darkroad]

I have a question for those of you that have done this. I have access to a mill and lathe. Whats the best way to cut .030 off the top of a 6.2 piston to lower compression? I fiddled around with it for about a hour the other day both in the lathe and the mill. Do I need to make a jig of some sort?
I remember someone saying that the diesel pistons are barrel shapped. I couldn't find a good way to get them mounted straight. Any help would be appreciated.


Thanks

Darkroad

[grape]

you need to make a set of aluminum jaws that grab in the oil ring groove, it is round and true to center.