On Sun, 07 Dec 2008 09:08:56 -0500, Ken Sterling wrote:


Saving the threads, even if it were possible is a waste of time,
because the
treads have become aluminum oxide and have no residual strength
anyway. Next time use anti-sieze at assembly. Most likely the fault
was electrolysis, as they were probably diecast and zinc is often
alloyed with the aluminum to promote flow in the mold. In the presence
of water, the unit becomes thousands of little batteries.

On second inspection; if I can't get the bolts out, it looks like
drilling the next size and tapping won't work. I'll have to make all
new. My version will be a bit beefier. What's the best bolt for AL with
an eye on electrolysis? AL bolts are too soft in small sizes. Is
stainless a good choice? or maybe brass?

Karl

Karl,
I run into this all the time.. .. .. and I've found out that the best
solution (if you have the room) is to drill, tap and install a stainless
Helicoil. A bit pricey, but ya only do it once. Ken.

One of my clients (aerospace) uses Kingserts almost exclusively for this,
with great success. I have no clue how much more expensive they are than
Helicoil, but they look a lot stouter.

BUT, anything that's going to be exposed to real weather gets stainless
to stainless (and lots of anti-seize on assembly).

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html