Ken Campbell Iowa
10 February 2019
rudely butting in ( g ) .. i thought lathe truing bases improved the accuracy of my 22 castings. i used standard 5c collet blanks bored to size in my hardinge chucker, chucked on the groove diameter as close to the base as possible ...very little chuck pressure and a very very sharp tool ... probably about 45 degrees of front rake ... to put the least load on the casting. alloy was 92-6-2 hardball not heated. i fed into the casting base axially to lessen the load.
i don't think it is critical the amount you take off within a couple thou, and the improvement was with and without gas checks added later . i also played with the base angle on plain base with no difference, they don't seem to need a 90 degree base, and i would fantasize that a bevel base doesn't damage so bad in handling.
however, i thought the same improvement came with " bumping " or " swaging " the bases flat in a die, and that was much less hassle .... well, after making a die, of course ...
hope this helps, i would like to see more reports on cutting or swaging " better " bases . the best cast groups in my 222 were with " improved " bases . this from base pour; nose pour might not need that ??