re: Re: swiss turning in minature?

Graham wrote:

>Dave, it is more the machine that I want to minaturise than the
>parts. The roller I mentioned was to be about 1mm in diameter but
>other parts may be smaller and accuracy is very important. It is for
>a 100:1 planetary friction drive for a 4mm (that's not the shaft but
>the diameter) motor.

>Marcus, thanks. It sounds like you know your stuff. I had wondered
>about using just a brass clock bushing that would be replaced often
>and held in a ball race. Then I could use say silver steel as a
>blank as it is fairly accurate. I can't help but feel there must be
>a dirty solution. Maybe a makeshift airbearing. Make or obtain an
>accurate bush, bore out some of the central section and apply
>compressed air through a cross drilled hole. This would still need a
>good blank material. I can buy hardened ground stock in the form of
>drill blanks but are unhardened blanks available?

I'm going to butt in here with my meager knowledge of air bearings. A small
air bearing is unlikely to be stiff enough to resist cutting forces. Small
as in 1 mm or less diameter.

Marcus had a good idea of using a follower rest, depending on the length of
the part this might work ok. A long skinny part would whip when you started
to cut the end, unless you rechucked it frequently.

I've seen a Hardinge Swiss type lathe without the stink Marcus mentioned.
Don't know what kind of oil they used, but it seems to me that motor oil
should have the right properties.

To get a tight fitting bearing for the bushing, why not try Babbitt metal?
Whatever size your stock is running, you can adjust the bearing to fit.
When it gets to where you can't adjust it any more, bash on the ends to
reduce the bore and ream it out.

BTW, there are different grades of Babbitt. The ones containing lead I've
heard are not as good as the ones that are mostly tin.

Let us known how this works out, sounds very interesting.

regards-

Elliot B.
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