Without know which specific alloy it is, one can only guess, but see:
my inclination would be to sandwich the tin in-between two pieces of MDF and then make a pair of cuts:
(make that cut with things clamped from the side)
(make that cut with things clamped at top and bottom)
attached as a v7 file.
cribbage_bottom_plate_v7.c2d (52 KB)