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Old 02-06-2017, 12:20 PM
James. V. D. W James. V. D. W is offline
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Default Advice needed!

I am currently busy with the hood from a 66 GMC. It was repaired poorly before and just filled over. I believe the metal was stretched and they shrunk it by hitting it multiple times with a pick hammer creating loads of high spots. I have tried planinishing, shrinking disc and heat shrinking. Nothing seems to work. I am at the point of just removing the damaged metal and replacing it. I need some guidance before I screw it up completely.

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Old 02-06-2017, 12:50 PM
Marc Bourget Marc Bourget is offline
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Gene Winfield demonstrated recovering from this problem at the Santa Cruz Metal meet, appropriate use of heat shrinking.

Look into the technique a bit more.
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Old 02-06-2017, 02:25 PM
AllyBill AllyBill is offline
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I'd put a big heat shrink in the middle of there to over-shrink it then stretch it back out with hammer and dolly.

Will
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Old 02-06-2017, 02:47 PM
James. V. D. W James. V. D. W is offline
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Quote:
Originally Posted by Marc Bourget View Post
Gene Winfield demonstrated recovering from this problem at the Santa Cruz Metal meet, appropriate use of heat shrinking.

Look into the technique a bit more.
Will try and find it. Thanks!

Quote:
Originally Posted by AllyBill View Post
I'd put a big heat shrink in the middle of there to over-shrink it then stretch it back out with hammer and dolly.

Will
I tried that with very little success.
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Old 02-06-2017, 02:51 PM
Marc Bourget Marc Bourget is offline
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Gene's approach, IIRC, was to use a series of point shrinks, HAZ not much bigger than the flame (small) strategically placed, interspersed with assists from a flat bar or spoon.
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Old 02-06-2017, 02:53 PM
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Steve Hamilton Steve Hamilton is offline
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I would think that each of the pick marks is a stretch, so a heat shrink at each would be a start. Maybe just a hammer & dolly first as some of the metal will shrink back as you level it out. To avoid stretching more use care to hit lightly in an off dolly approach. A ring noise indicates on dolly contact. Many light hits (15-20) per pick mark is far better than a few heavy hits. Place the dolly on the concave side of the pick mark for best results.
If the area is concave when looking at the outside of the hood, try to pop it over center so that it is a lump sticking out, it is much easier to work on. Also a shrink disk needs to make contact with the stretched metal(the lump) in order to get a shrink.
Good luck
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After looking at your photos again that area could very well be over shrunk! If it feels tight and will not pop up over center, it may need to to be stretched.
Think of the hood as a low crown arch,or dome, a stretched area will usually rise up above the contour.

Was there possibly a carburetor fire that caused the problem, often a rusty area where the paint burned off on the bottom side.
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Old 02-06-2017, 03:57 PM
crystallographic crystallographic is offline
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... nice wood grain finish....
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Old 02-06-2017, 07:17 PM
AllyBill AllyBill is offline
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Looks to me like someone tried to shrink it before and it didn't go well.

My technique is to work on the naturally raised side of the panel, warm it through to raise it further and give shape and strength that you can work against then pre-heat a crowned hammer. Don't want a cold hammer sucking the heat out of the job. Next, bring the raised area up to smoking hot then make the centre of the crown a dull red.

Don't forget, rule 1, page 1 of heat shrinking.

It's not about how hard you hit it, it's all about how FAST!

It's like doing a belly-flop in the pool. It stings because the water can't get out of the way and that's what you want the metal to do. You want it to have nowhere to go but back into itself and shrink. Hold the hammer mid-shank and crack it like a whip, faster the better. This is where I think whoever worked on that job before went wrong. They got it hot then hit it slowly so all you get is another stretch.
The resulting dings won't look pretty at first but quickly swap out for a flat hammer (heat it first) and get a piece of smooth hardwood on the back of the panel, Iroko is good, and planish into the wood working in a circular fashion inwards towards the point of initial impact and the area you first shrunk will act like a black hole and suck in all the unwanted metal.

Good luck.

Will
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Old 02-06-2017, 07:29 PM
cliffrod cliffrod is offline
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Quote:
Originally Posted by AllyBill View Post
Looks to me like someone tried to shrink it before and it didn't go well.

My technique is to work on the naturally raised side of the panel, warm it through to raise it further and give shape and strength that you can work against then pre-heat a crowned hammer. Don't want a cold hammer sucking the heat out of the job. Next, bring the raised area up to smoking hot then make the centre of the crown a dull red.

Don't forget, rule 1, page 1 of heat shrinking.

It's not about how hard you hit it, it's all about how FAST!

It's like doing a belly-flop in the pool. It stings because the water can't get out of the way and that's what you want the metal to do. You want it to have nowhere to go but back into itself and shrink. Hold the hammer mid-shank and crack it like a whip, faster the better. This is where I think whoever worked on that job before went wrong. They got it hot then hit it slowly so all you get is another stretch.
The resulting dings won't look pretty at first but quickly swap out for a flat hammer (heat it first) and get a piece of smooth hardwood on the back of the panel, Iroko is good, and planish into the wood working in a circular fashion inwards towards the point of initial impact and the area you first shrunk will act like a black hole and suck in all the unwanted metal.

Good luck.

Will
Heated hammer makes a lot of sense. How do you heat it and keep it heated- torch, hot plate, ?
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Old 02-06-2017, 08:25 PM
crystallographic crystallographic is offline
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And what to do with the smoking stick left in your hand after that first shrink?
(I only ask from previous experience ....)
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