Hi Amy,
Not that big, all things being equal.
Meanwhile, that Harper press is just a dressed up Harbor Freight
1ton arbor press. Can be had for about $50. I use something similar
to do mine.
(The only big thing was drilling a hole down the axis of the square
bar to hold the stamp.) If you don’t have the gear to handle that,
it wouldn’t take much to have a machine shop do it for you, to any
size you need. Just because your stamp came to you with an 8mm square
shank doesn’t mean that there’s any reason it needs to stay 8mm
square. You’re a metalsmith, right? It’s made of metal. Make it do
what you need it to do. Grinding off the edges of the square (to
make an octagon) will get the size down fast, which may well let it
fit in the Harper press if you want to pay for one. Otherwise, just
get your own arbor press (check Craigslist) and have someone drill
out the shaft to hold your punch. (and put in a set screw to retain
the punch.)
If you’re really hunting for serious presses for your stamp, a fly
press is the way to go, but they require the ability to make tooling
to set them up. (and they’re generally big & heavy.)
If you have any questions about how to gimmick the arbor press, drop
me a line, and I’ll take a couple of pictures of mine. It’s dirt
simple.
(But needs either a metal lathe with 4 jaw chuck, or a reasonably
good sized drill press and a DP vise.)
Regards,
Brian.