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.