On Fri, 20 Sep 2013 19:41:27 -0500, "RogerN"
wrote:

"Ed Huntress" wrote in message
.. .

On Fri, 20 Sep 2013 17:28:49 -0500, "RogerN"
wrote:

snip

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I used to have a Testors BD-5, can't remember if it had a shaft extension
or
not.

Some of my R/C helicopters have a shaft drive to the tail rotor and use
arrow shaft. Some use aluminum, some carbon fiber arrow shafts. These
aluminum one have inserts, can't remember for sure if they are glued in or
shaft internal, collar external clamping to the shaft. I would consider a
carbon fiber arrow shaft with aluminum fittings epoxied on, perhaps JB
weld
or other strong epoxy. You may want to look at some R/C heli parts, lists
and exploded views are available online.

RogerN

JB Weld is not a strong epoxy. It's an ordinary amine-cure epoxy
that's filled with steel powder, and its strength is typical -- less
than 4,000 psi under ideal conditions.

They make some wild temperature claims for it, but my guess is that
they're talking about the temperature at which it breaks down and
begins to carbonize -- 550 deg. F. It's lost all useable strength long
before you reach that temperature.

--
Ed Huntress

Why do you need a stronger epoxy for an .049 engine?

I don't know if you do. I was commenting on JB Weld. It's good stuff
that solves a lot of problems, but I've heard from many people who
think it's a "strong" epoxy. It's not. It's run-of-the-mill in the
strength department. Elmer's two-part epoxy probably has the same
strength.

The engines on my R/C
helicopters include .60 2-stroke and .90 4-stroke and I've never had a drive
shaft failure from JB-weld of the fittings in the tail rotor drive shaft.
My tail rotor blades are around 10-12" swing with variable pitch, the models
are 10-11lbs, they shake if out of balance, still the JB-Weld or other
4000PSI epoxy has never failed, the shafts get destroyed in a crash but
never had an epoxy failure so far. I haven't had that good of luck with 5
minute epoxy.

No surprise. Five-minute epoxy is very compromised for the sake of the
quick cure. It's weak, it can be brittle (depending on brand and
formulation), and it's usually not even waterproof. A standard
slow-cure, room-temperature cure, amine-cure epoxy is very waterproof.

Note my drive shafts are supported at each end, I'm not sure
I'd want a 5" extension on an .049 without support. Also my tail rotor
shafts aren't close to the engine so there is no high temperature problem, I
doubt an 049 would get very hot on the shaft, never had problems with props
melting or anything like that.

On a side note, some have had problems with the muffler coming loose on the
4-stroke engines, they use JB-weld and it holds up on the exhaust pipe of
the model engines.

RogerN

Roger, I'm just telling you what the measured properties of those
materials are. They're well-known in the adhesives field. I wrote a
12-page report on them years ago for American Machinist, but these
basic epoxies haven't changed. They've been the same materials since
the '60s.

JB Weld's metal filler probably provides some advantages in a variety
of situations. Bond strength is just not among them. And the ability
of amine-cured epoxies to tolerate high temperates doesn't vary much
among brands.

--
Ed Huntress