"Peter Grey" wrote in message
.net...



"Harold and Susan Vordos" wrote in message
...
An operation such as that is
called trepanning, where you remove a core piece without reducing it to
chips. It can be accomplished easier with a boring head, but even that
can

Harold,

Are there bits commonly available for trepanning in a boring head? If I
wanted to make one, how would it be shaped? I'd start with round stock so
that it could be mounted in the head, yes?

Regards,

Peter


I was faced with this challenge years ago, when I built a gasketed filter
press for my gold refining operation. I had to cut about two dozen
washers from an unknown (austenitic) stainless material, roughly 3/16"
thick. Finished washers were roughly 3" diameter, with a bore of 1-1/2" as
I recall. The press is long gone now, having been sold along with the
refining business I sold when I retired, so I may be off on the sizes. No
matter, the principle remains unchanged.

I used a 3/8" HSS end mill shank, on which I ground what resembles a parting
tool for a lathe, with a slight cant to the cutting edge, so it would leave
a very thin section on one side of the part being removed (the washer), so
there was little material to machine afterwards. You stop cutting before
breaking through to avoid the tool binding on the part being removed from
the stock, and the thin section makes it easy to get the piece out. The
problems of cutting stainless in this fashion were difficult to overcome. I
ended up buying a BoeLube setup, which solved all the machining problems.
Sulfur oil alone wasn't adequate. That would likely not be true on other
materials.

One runs the boring head very slowly, using the finest feed. With a chip
breaker properly ground in the tool, it works great, but would certainly
become a serious challenge if the cut was very deep. There's considerable
chatter, due in part to the rather flimsy setup. You can often eliminate
the chatter with proper speed and feed selection, however.

One of the things you have to address is considerable side clearance on the
tool, where it must clear the radius of the cut on the outside edge of the
circle. The tool looks somewhat odd, but works fine. Should you decide
to try it, remember, the material you select for your tool will leave the
tool edge ahead of center unless you reduce it at the point of the cut to
the centerline of the tool. That the cutting edge is on center, or not,
has a serious effect on how the tool sees the material, and the relief
angles. Does this make sense to you? If not, lets talk. It's important
that you understand it well.

Harold