On Mon, 29 Aug 2011 16:20:09 -0500, Tim Wescott
wrote:

I kinda asked this question once before, and got a bunch of answers that
all seemed off the point. So I'm going to try again, and (hopefully)
make my question specific enough this time.

Everybody tells me "use 12L14, it's really easy to machine". I'm willing
to accept that -- I'm using steel that I get surplus, and there's a wide
range of machinabilities that I'm experiencing; I can certainly see how
using the _right_ steel might make a significant difference. But:

If I take some annealed or normalized 1065 steel (or other 10"something
big" steel), get it to the shape I want, and properly heat treat it, it's
going to be a _lot_ harder than when I started. So assuming that I can
machine it in the first place, then get it to hold its shape (or correct
its shape after the fact) and not crack in the heat treat process, I'm
way ahead.

On the other hand, if I take 12L14, get it to the shape I want, and do
the _very best heat treat in the world_, then -- because of the low
carbon content -- it's not going to be much harder. Right?

What about 1144 or 41L40? Do you get much by heat treating these? How
easy are they to machine compared to 12L14? Why isn't there a 12L50?

I've heard tell that 1144 isn't as strong as other steels of similar
carbon content -- true? What about the mechanical properties of 41L40
after heat treat?

I'm basically looking for a steel that'll be suitable for model airplane
crank shafts. The advice that I get from the hobby builders of model
airplane engines is "use 12L14 and don't crash". I'm not going to
discount this -- but it'd be nice to be able to do something on par with
what I buy at the store. So, basically, something that's easy to
machine, but that'll harden up to something between a grade 5 bolt and a
grade 8 bolt.

Id use 4140 or 4340 (annnealed) or (pre hard) for model airplane cranks.

Its not all that hard to machine, even with a small weak lathe. Just
dont take huge bites when cutting it. Take your time.

Heat treating is easy enough when you are done and any finish work can
be done easily enough.

Id NOT use 12L14 for this application. No way.


Gunner





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