Unsticking the Stuck, Part 1

Sometimes nuts, bolts and screws just get stuck, and no amount of effort will unstick them! I previously posted about a visit to Jack's Auto and Aero, to enlist Jack's help with stuck nuts on my exhaust system, and some serious seized brake lines. What I didn't tell in that post was that there was one more stuck bolt, and it is still stuck.


It's one of the six bolts that holds the half-shaft to the differential. When I was changing the shocks and springs, I followed the Bentley manual's procedure to remove the half-shaft bolts, to keep from stressing the half-shaft when pushing the control arm down to install the new spring. That worked great on the driver's side, but on the passenger side, one of the bolts (which have splined Torx heads) just stripped right off, leaving a semi-smooth cone. I tried various vise grips and so forth, and so did Jack, but neither of us could budge it. I wound up having to pry the control arm down enough to get the spring in.

I was talking to Kelly Williams about the problem, and mentioned the idea of welding something to the bolt so I could turn it. He said, "I've had to do that twice already - I'll give you the name and number of my machinist." And he did.

Since I'm now a machinist too, I decided that a great project would be to prepare the piece to be welded. That should save some money too, since the real machinist won't have to do it. I decided to use the heads from the large bolts from the piece-of-junk Harbor Freight spring compressor which seized when I tried to use it. I cut the heads off, and then started milling it down to something flat and thin. Milling would also remove any galvanizing that might effect welding:

I quickly learned that I wasn't very good at controlling depth of cut. Part of the problem is that in any lathe or mill, there is "backlash" in the controls, which effects your ability to make it move precisely. But I gradually realized that it was more than that - there is stiction (friction that makes it stick) in the mechanism that keeps it moving the full amount. That later rears its head as a big jump in movement that takes far too big a bite!

Real machinists have something called a "DRO" - a digital readout that tells them very precisely (to the ten-thousandth of an inch) how much the mechanism really moved. I found an article about a "poor man's DRO" that used a digital tire tread-depth gauge, which can be bought on eBay for about 10 bucks. I bought two.

The basic idea is to take the spring out of the gauge so the arm slides very freely. You glue magnets to the back to hold it to the machine, and another magnet to the sliding arm so it sticks to the part that moves. I also cut off the ears that were molded into the body of the gauge, so it would be narrower:

I can stick the gauge to the column of the mill, and stick the movable magnet on the milling head that slides up and down. That way, I can tell very precisely (this has readout to half a thousandth) how much it moved - or more to the point, didn't move:

Now that I could tell what I was doing, I was able to cleanly machine the bolt head to about 3/16" thick - easy to weld, but thick enough that I can put a socket on it and try an impact driver to loosen the bolt. Then I chucked it in the lathe, and drilled a starter hole in the center. Next time I have the Z3 in the air, I'll measure the head of that ruined bolt, and drill a hole that is a tight fit. Then it's off to the welder's!