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how not to attach a strain gage

Posted: Mon Feb 04, 2008 6:15 pm
by mtngun
from the old forum:

Some of you will probably get a Pressure Trace eventually so maybe you can learn from my mistake. :oops:

You are only supposed to use particular adhesives to attach the gages. The instructions make that quite clear. Most of the approved adhesives are priced as if they contained diamonds and gold, but JB weld is approved, and it\'s cheap, so I ran to the local department store in search of JB weld. They didn't have any, so I got another epoxy instead, Permatex 4 minute multi-metal "perma-poxy". It's rated at 5000 psi which is pretty good. It merely had to stick a wimpy little gage onto a barrel. What could go wrong?

But it produced a bad trace, extremely noisy and 110,000 psi on a load that should have been safe. What the heck !!!

Jim Ristow at RSI advised me that quick-set glues tend to be brittle and prone to cracking. Oooops. :oops: :oops: :oops:

Image

Indeed, as Jim suggested the glue was cracked along one edge, and when I pried at the crack with a knife blade, the whole shebang popped off the barrel.

I'm just relieved that the problem has been identified.