"John R. Carroll" wrote in message
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"Buerste" wrote in message
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"Gunner" wrote in message
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On Thu, 4 Dec 2008 00:07:25 -0500, "Buerste" wrote:


"JoanD'arcRoast" wrote in message
news:031220081412052869%JoanD'arcRoast@biteme. org...
I shape my wood lathe tools by hand, and then heat treat in a campfire
and quench in used motor oil.

I have access to LN2, but wonder if it would make a noticeable
improvement of the O-1.

I know I will encounter inefficiencies due to Leidenfrost effect, even
if I pre-chill the steel to minus 80 C. (Perhaps I can roto-vac to
make
slush, I'll have to explore that.)

Opinions?

Do you think my methods are too primitive and hit-or-miss to achieve
better sharpness and edge retention on the lathe tool?

Am I barking up the wrong tree? Would the little extra hardness gained
not be desirable for this application?

Pointers? Links?

Thanks for taking the trouble to read this mess,
-j

I've heard from experts that cyro is smoke and mirrors. The best thing
said
is cyro provides superb stress relief. Your application and your level
of
correct heat treatment limits what you can do. Send stuff out to a heat
treater. Your expectations are too high for home-brew.


In some rifle barrels...cryo works wonders for improving
consistency...IE accuracy.

Ive several that were cryo 'd and got significant improvements in
group size. Though both were high quality barrels in the first place.

A buddy had a stock , early factory barrel done, and while the
accuracy was improved....not all that much. There were more issues
than just stress relief involved in its inability to shoot extremely
well.

Gunner


Years ago, I made a batch of twelve 8" x 7/8" D-2 rotary wire cutters.
Half we had cyro treated after there were all heat treated and triple
drawn. We kept logs that showed no improvement in life between
sharpenings. I talked to my friend George at IVAC, the TiN coating
company, and he explained cyro to me. It has it's uses but it's just not
magic.

I'd agree that it isn't magic. You didn't properly sequence the
operations, however, so you don't really know the relative benefits in
your application. Apparently you either didn't understand what Fisher was
saying, discussed this with him after the fact, or he really doesn't
understand either.

Cryogenically treating materials isn't done in order to increase hardness
Tom.
It also has little value in isolation. It's what you are able to achieve
before hardening an temepering that is affected and the difference can be
remarkable.

I don't know exactly what the impact on your rotary knives would be in
terms of life cycle but if an extremely uniform cutting edge would make
any difference, you'd benefit to some degree. You might, of course, find
it necessary to refine your process. It's likely that what you do now
reflects the result you have ordinarily been able to achieve in the past.
In other words, it wouldn't have paid you in the past to refine your edge
geometry in ways that the material didn't supoport very well when you put
an edge on it.

Think about the value that a very uniformly loaded cutting edge would
yield or a cutting edge geometry that you couldn't otherwise produce
consistently even for the length of a single knife.

That is the sort of thing cold cryo locking can add and that result may or
may not have value in your particular application.

JC


Send me some links if you have something handy, I'll revisit the whole
thing. The knives are 8" diameter x 7/8" thick with a 4" bore. We then cut
little 60 degree "teeth in the outer surface of half of the batch of 12
about 1/4" apart x 3/32" deep. These teeth help grip the wires and feed
through two of these knives in a rotary shear arrangement. The knives are
powered by 10 hp. The other 6 are left smooth. After heat treating, the
blades are ground with a 1 degree angle from the OD to the ID. I do this on
a rotary surface grinder. The blades are pressed together under high
pressure and overlap by about 1/4". The operator typically feeds 1" dia.
hanks of .010" to .025" tempered wire through the intersection of the
blades. Cuts it like a laser! As the blades get dull, the outer corner on
the smooth blade rounds off and the gullet of the teeth on the toothed blade
rounds off. We then regrind the 1 degree in the sides until they are sharp
again. We'll grind them until they are 3/8" thick or break from the preload
pressure. A batch of 12 blades lasts about 5 years for each of four cutting
machines. But, they cost a fortune for material and take a long time to
make so any improvement helps.