Maybe you’ll believe Dick Maury…
Actually, if you heat a spot cherry red it will initially expand, but the mechanical forces will cause it to contract a greater amount when it cools. You often see this on rear axle tubes (sometimes intended) when a bracket is welded to one side of the axle tube. When it cools it will curve. First time I saw this in action was in a poorly designed industrial furnace at a Ford Motor Company assembly plant. The design did almost nothing to insulate the floor and 10’ x 8’ door frame from the 1,100 F internal temperature. In operation, the floor arched up (concave) in the middle. When it cooled it went convex, producing enough force that it ripped the substantial anchor bolts out of a reinforced concrete pad.
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Heating metal and then quenching it actually shrinks it. Just removing the heat does not. As anyone that does old school body work. If you have a high spot on metal, you heat and quench until it is shrunk and flat. Same principle applies here .Heating expands it but the quenching contracts it more than the metal expanded. Work on the side of the pipe that you want to get shorter. Rear side for more toe out and front for more toe in. This can be done on the car if you are careful, even with the alignment equipment hooked up so you can watch the change.
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Yep: Smokey Yunick used to do it to solid rear axle tubes, to impart a bit of negative camber. The advent of Torrington double row spherical roller bearings made it even better!
I watched old time hot rodder and master machinist, Tom Peaty, do the heat/quench shrink on a drive shaft he made for us. The blown Olds powered belly tank lakester at the back of the shop.
Decades ago, in my former profession, I stopped at a small collision shop in a small town to check on a car. i had OK’d repairs and worked out the estimate for the fix. It incuded a new front fender. In my judgement, cheaper than straighten. Lo and behold the body guy and the owner were there. The body guy in the midst of straightening the fender. using the heat/quench method to remove high spots. Each guy a bit chagrined at being “caught”!!! Naah, Ok by me if each of you is OK with it. a lot more work that way, but…
Clearly, the shop guy was quite skilled. the work looked great…
Carl
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There are no rear toe adjustments, Mark…
The wishbone pivots on the inner pivot mounting shaft - parallel to the cars centreline. And at the outer end the hub carrier pivots on the pivots on the outer pivot shaft - likewise parallel to the cars centreline. All of which is meant to keep the wheel parallel to the car’s centre line - with a small tolerance allowed, toe spec.
Noting that both rear wheels should of course be within specs - or something is wrong. The fault may be misaligned rear cage, bent parts, worn bearings - or whatever you can imagine. To be rectified to get the toe within specs - and brute force ‘adjustments’ may compromise structural integrity. The function of the radius arm to take part of the load off the pivot points…
No need to emphasise that rear wheel steering to toe misalignment - or loose joinery…
Frank
xj6 85 Sov Europe (UK/NZ)
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Sure, Mike - but such heat treatment interferes with the structure of the metal, and may weaken it. Which is OK in some cases where structural strength is not an issue - or load stresses have other paths. But the whishbone, in this case, is a single piece that holds the suspension together…
Besides; rectifying faults by makeshift repairs runs the danger of countering one fault by introducing another - making the result twice as bad. Which is OK if the fix is meant to be cosmetic - structural consequences being immaterial. It’s a vast difference between inconvenience and a disaster…
In short; if the rear toe is out of spec - don’t cheat…
Frank
xj6 85 Sov Europe (UK/NZ)
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I’m only explaining the physics, not suggesting the procedure.
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Neither would I, Mike…
Frank
xj6 85 Sov Europe (UK/NZ)
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Hello Dick,
With respect, that is not correct. Its the localized heating and the unyielding surround metal that results in shrinking of the metal in the hot spot,
When carrying out a Hot Shrink in sheet metal, a small spot is heated to Red Heat (plastic state). If its a Convex Shape, normally the Hot Spot will rise (it can’t expand out due to the surrounding, unyielding metal) and without doing anything else, some shrinking in the Hot Spot area will occur due to the Plastic State material compacting because its expansion is resisted by the surrounding steel. Further shrinking can be brought about by hitting the raised Hot Spot Down onto a dolly flatter than the contour of the panel. This exacerbates the shrinking by compacting the metal in the Hot Spot whilst in the Plastic State. The dolly is there only for support when hitting the Hot Spot, Hitting too hard on to the dolly will stretch the metal.
Cooling the metal is more about getting it cool enough to bring the overall contour back to its normal shape (unexpanded) and to allow you to run your hand over the panel to judge how the shrinking is progressing.
I’m an old school practitioner and taught Coach Building in the past. When teaching how to Hot Shrink, I would demonstrate the affect of heating metal to the Plastic State whilst its being resisted by surrounding material, by the following method:
- Take a short length of Mild Steel bar, say 50mm of diameter 20mm.
- Place it in a vice so the bar is being gripped by its ends. Only tighten the vice enough to hold the part from falling out and to resist any axial expansion of the part.
- Heat a small area in the centre (axial) of the bar to Dull Red.
- Go and have a cup of coffee, or a beer and by the time you return, the short length of bar will be either on the floor, or resting in the bottom of the vice frame.
The part has been allowed to cool naturally and it has shrunk in length. It could have been cooled rapidly with cold water, but the result would have been the same. Further, if you cool the Hot Spot very soon after heating, some of the shrinking can be arrested, by removing the metal from the Plastic State and therefore, halting the compaction of the Hot Spot area of metal.
The same principle exists when removing cylinder liners, or bearing cups in a bore, by running beads of weld the length of the cylinder, or around the inner circumference of the bearing cup. There is no requirement to cool the weld bead area by quenching with liquid, simply removing the heat source and allowing to cool naturally in air will be sufficient for the part to fall out. The Shrinking has already occurred during the heating stage.
Regards,
Bill
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