"RogerN" wrote in message
m...
"Ed Huntress" wrote in message
...

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

snip

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.

What I was calling "strong" is relative to what's commonly available. In
hobby shops and local stores the 2-Ton epoxies are about as strong as I've
found. So what's with the strong epoxies and why aren't they readily
available in stores? I'm guessing either expensive or dangerous, still it
would be nice to have stronger options where the others don't hold.

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.

I've had 5-minute epoxy fall apart after a few years, the nitro-methane in
the fuel seems hard on a lot of things, not sure about 5-minute epoxy.

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

Thanks, great information to have, it's good to know there are stronger
epoxies that the hobby shops don't sell. Any info on the stronger
epoxies, where to get, PSI strength, etc.?

RogerN

The consumer grade epoxies are a compromise between being strong and being
idiot proof.
The higher strength ones are not trying to achieve a 1:1 mix ratio and are
usually pretty sensitive to variations in the ratio. Typically, they have
2:1 to 10:1 ratios. You can't just squeeze two ribbons out and mix. Usually
you have to mix up a large enough batch to guarantee a proper mix regardless
of how big the job is.

They come in Quarts and have a shelf life. Some companies have special
syringe dispensers in the proper ratio but they use a special gun and a
mixing tube.
All of this is tough on your average consumer.

Paul K. Dickman