On Oct 24, 12:43*am, Don Foreman
wrote:
A younger friend and former colleague and teammate of many years came
over today for *a bit of shop assistance. * He was doing a brake job
on his Subaru Outback, *twisted the head off a bolt in a caliper
mount. *Fortunately, he was able to get the caliper mount, a steel
forging or cast iron but probably a forging, *off the car to bring it
to me. * *There was a pretty good stub available to grab with vise
grips, *but that baby was stuck. *I knew that if he twisted the head
off with an impact wrench, *screwing around with Kroil and visegrips
wasn't gonna budge it unless maybe it soaked for a week. * *

Bob said he'd tried heat from a torch with no success. * Hm. * Then I
realized that his torch was probably propane/air or at most MAPP/air.
My experience has been that if I can get the bolt and the metal it's
stuck in glowing dull red, *it will come out without much of a fight.
Heat above 1200 degF heat must do something to rust. I put the forging
in a bench vise, snugged it *up good. * Clamped a big *round-bite
visegrip tight on the stub. * I didn't even go to the bigger Smith
torch, just put the #4 tip on the Meco Midget aircraft torch (I love
that little torch) *and started heating. * Had a visegrip on the stub..
When the metal started to just perceptably glow after a few minutes, I
started trying to rock the visegrips. *After a few yanks, something
moved just a teense and I knew we'd be grinning in a minnit. * Just
keep the heat on, keep jiggling, don't get impatient. *Soon it was
twitching, then rocking a few degrees, then rocking 90 degrees, then
120, *then I just wound that sucker outta there. * I didn't want to
get hotter than very dull red because I wasn't sure it wasn't a
casting and I didn't want to start any cracks if it was. *I about
can't imagine using a casting on a brake part like that, but one never
knows. *

I figured if heat didn't work we could always drill it out and retap
the hole, but heat has nearly always worked for me when I could apply
heat. *(Aluminum castings can be problematic.) *Turns out *drilling
and tapping wasn't an option here because it was an unusually fine
thread: * M12-1.25. *Standards are 1.5 and 1.75mm pitch. I don't have
a M12-1.25 tap and I'd be amazed if the auto parts store had one. I
could make one, but that'd take a little while. *

NAPA did, however, *have grade 8.8 *M12-1.25 bolts so we lucked out
there. * Bob and the guy at the store thought that wasn't the right
bolt because Bob's good bolt wouldn't go into the "test nut" at NAPA.
I said it's the right bolt. *They said it's wrong because they
couldn't get it into the nut with finger force. *I said it's the right
bolt, Bob, buy the bolt. * I miked the two, OD's were within a thou of
each other. *I laid one on the other, the threads were blackout for
more than six threads. *It's the right freakin' bolt, there's just
some crud in the roots of the old parts. *

He bought the bolt. * When we got back, it didn't go into the forging
easily. *Bob is a very good engineer, not ham-handed or *a "get a
bigger hammer" sort of guy. * He's also a fine craftsman in wood. * I
showed him how we could make a tap that, while not good enough to cut
threads, could clean and restore them. * I took his stub, *cut four
longitudinal grooves in it with an abrasive cutoff wheel in a
pneumatic die grinder. * That produced sharp edges that could scrape
internal threads. * *I wound that into the hole on the forging with
visegrips, *rocking it about 120 degrees as I progressed until it was
projecting well out the other side. * Invited him to try the new bolt
now. * He wound it in with thumb and forefinger, grinned. * I
suggested he keep that *"thread cleaner" *for next time. *

Later, I decided to see if I could fix the speakers on Mary's 'puter.
They're powered speakers, *have developed a hum. *Probably an
electrolytic cap, right? * Proceeded to disassemble the one with the
elex within. * Found I don't have a Philips screwdriver with a shank
long enough to reach down in a hole to the screws. * Mmmph. * But I do
have a number of #2 Philips bits. *I grabbed one of those, *cleaned
off the back end, and silver-brazed it to a piece of 1/4" mild steel
rod about a foot long. * *Turned out that wasn't quite reaching the
screws because the screwdriver bit was bottoming in the tapered
plastic *hole. * Chucked it up in the lathe, *found one remaining good
cutting edge on the triangular carbide insert that was in the Aloris
holder, *knocked the corners off the screwdriver bit and took off a
few thou beyond that. *It wasn't exactly coaxial on the steel rod as
you might imagine, but not bad considering the silverbrazing *was done
by eyeball with two drillpress vises on a firebrick. * *That worked,
the screws came out without a fight. *

Your story reminded me of reading those of Gus Wilson and his Model
Garage in Popular Science when I was a kid.