Tim, if you haven't had the mill head column off of your machine to improve
the metal-metal contact area to the headstock top surface, you might
consider doing this procedure to gain some rigidity when milling.
The one I worked on was a 12x20 made in 1999 maybe.
While you're milling something fairly aggressively, put your left hand
fingertips at the seam of the contact surfaces at te base of the column. If
you feel movement, this procedure may increase milling rigidity
considerably.
The mating surface of the column flange is likely fairly accurately flat, as
it was probably turned (faced) on a lathe.
The top surface of the headstock may be one of those areas where a factory
worker ran a power scraper on it, just to smooth it somewhat, followed by
filling the seam gap with filler putty.
I managed to get the headstock surface flat, by rough filing, and checking
for contact area with plain printer paper laying on the headstock surface,
and rubbing a (machined flat with a large shell mill on a large machine)
flat thick slab of aluminum on the paper to make a carbon copy (although
aluminum oxide) of the contact area.
I put cardboard and shop rags in the opening to catch the filing swarf.
When I started, there was probably only about 15% contact between the two
surfaces.. when I had finally had enough exercise, the contact area was
probably closer to about 75%, and the rigidity of the mill was increased
greatly as a result.
--
WB
..........
"Tim Wescott" wrote in message
...
It's more that there's really no way to cut the center of the circle --
the best any drill bit or center cut mill can do is sort of mash the metal
out to where it can be cut, and to minimize the amount of material that
has to be so "mashed".
I'm no machinist, so take these with a grain of salt. But here are some
solutions that I can think of:
1: get a more rigid machine to work with. I can do what you're talking
about just fine in aluminum on a Smithy "3 in 1" (lathe, drill, lousy
excuse for mill), but I doubt it'd like me trying in steel.
2: Check your alloy -- are you using one of the absurdly easy-to-cut
alloys like 11L14? Can you?
3: Pre "drill" with a smaller mill, let it walk around, then finish with a
larger mill.
4: Put the part in a rotary table, and come down in the 'z' direction
while rotating the table -- this will keep your cut moving around, and
should make it easier on the machine.
5: I assume you'd be doing this already if you could, but consider
drilling a 1/16" pilot hole, and milling down over that. It'll leave a
hole or a dimple in the middle of your big hole, but even that small of a
pilot hole should span what your mill really can't easily get through.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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