On 1 Dec 2005 13:32:59 -0800, "ducque" wrote:

Since I'm completely self-taught at machining, there are necessarily
big "holes" in my knowledge. Here's one, and I'd like to "fill the
hole"! :-)

I don't know how to accurately make a very thin part -- for example,
something akin to a washer, or a very short bushing.

It's easy enough to accurately turn the part, make necessary shoulders,
etc. But what about after the piece is "parted off"? The desired part
will be too thin to hold effectively in a vise to mill to its final
thickness (imagine needing a part less than 0.050 thick, for example).


For example, using my milling vise and parallels, I cannot effectively
grip and strongly hold anything less than about 0.065 thick.

What do people do in these situations? Thanks.

In The Home Shop Machinist, Projects Two, Page 22, (Available from
Village Press), D. E. Johnson wrote a piece on "Machining Thin Disks
and Rings. His is a three step process that results in a part of
proper diameter and thickness, but does require a hole in the part.
At the risk of getting flamed for "disseminating copyrighted
material", a paraphrase of the steps follows.
Step 1:
Chuck a piece of stock and turn a stub end, OD to the diameter of the
hole in the finished part and length to allow re-chucking after step
two. Face the shoulder as it will be one of the finished faces. Drill
a hole, centered in the part and as deep as the stub length + the
finished parts thickness + say 1/8". (This hole diameter should be
large enough to allow a boring tool to enter)
Step 2:
Part of the piece allowing for enough material to finish the
thickness. The drilled hole should be deep enough to meet the parting
tool. The result, in cross section, is a 'T' shaped piece with a hole
through it.
Step 3:
Reverse the part in the chuck, chucking now on the stub, finish the
parts OD. Face off to the parts thickness and clean up the edges.
With a boring tool, enlarge the hole to meet the OD of the stub.
Quoting Mr. Johnson here, "... the finished part will fall off leaving
only a slight burr for cleanup. Feeding the boring tool in at an
angle using the compound will produce a countersunk hole"
I've used this process a number of times with good success. It takes
a little longer but the results are worth the time. YMMV

Regards
Bob
rgentry_at_oz_dot_net
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