To replace or not to replace: roof skin on 77 Trans an - Page 12 - Hot Rod Forum : Hotrodders Bulletin Board
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  #166 (permalink)  
Old 04-30-2017, 05:49 PM
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I can't tell much by the pics and have never done what you are right now so I have nothing helpful to offer. Finding the spot, for me, usually happens when looking closely at and feeling the surrounding areas while mashing on the bubble or dent.

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  #167 (permalink)  
Old 04-30-2017, 05:51 PM
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So U push down on the dent and while its oil canned in your looking for surrounding high spots?

Whatever spot or spots are causing my issue must be really small. I can't find em. Guess I'll just shrink the crap outta the area.


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  #168 (permalink)  
Old 04-30-2017, 06:09 PM
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Ok, here is my two cents worth. All from a guy who has never used a shrinking disc.

I believe you are having issues because you are playing with a flat test panel. Auto body panels are never completely flat. When you shrink a spot on a flat panel there is no place for the stress to come from so the whole panel os ending up with stress

If you put some crown in your test panel then the area you shrink can pull material from the surrounding area and you would not be fighting the oil can. What you will have is a low spot if you over shrink the panel. Also, any minor low spots should be tapped up high and the shrinking disc run over it again. Repeat this proceedure until there are no more low spots and you should end up with a banel that is close ot perfect.

John
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  #169 (permalink)  
Old 04-30-2017, 06:17 PM
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The spot you're hunting will be the place where the metal doesn't act like the rest as you push down on the bubble or up on the dent. The last spot that moves before it blomps and turns inside out. That may not make sense but it's my best description. I am used to huge panels that are caved in though, not little golf ball dents. As far as when to say it's finished... Ask yourself "Have I done my best?". IF the answer is yes, be satisfied and move on.
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  #170 (permalink)  
Old 04-30-2017, 06:22 PM
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Well, I just went back and reread the last couple of pages and realized I was assuming things that are not correct. My bad. Sorry about that.

I do believe though that you are asking a lot of a shrinking disc to shrink a large area that has been raised on an English wheel. That would take a lot of heat on an awfuly big area.

John
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  #171 (permalink)  
Old 04-30-2017, 06:36 PM
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Quote:
Originally Posted by John long View Post
Well, I just went back and reread the last couple of pages and realized I was assuming things that are not correct. My bad. Sorry about that.

I do believe though that you are asking a lot of a shrinking disc to shrink a large area that has been raised on an English wheel. That would take a lot of heat on an awfuly big area.

John
Is this the test panel still?
If so, the disc cannot flatten that down all the way.

I thought it was the roof skin.
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  #172 (permalink)  
Old 04-30-2017, 06:51 PM
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To replace or not to replace: roof skin on 77 Trans an

The pics from today concern the roof skin. The before and after pics are of the roof skin dents. No more test panel.

John long, so over shrinking will make a low spot? I guess that makes sense. It's certainly what's happening.

IDJ, so when I push on the dent you say the last spot that moves...so are you saying it's some spot on the edge/border of the oil-canning dent, or is it the spot I pushed on?

Also, back to the point of over-shrinking; could it be that this whole area is over-shrunk? It's right next to dent #3.

Last edited by Schroeder; 04-30-2017 at 06:59 PM.
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  #173 (permalink)  
Old 04-30-2017, 07:14 PM
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On a high crown area, over shrinking will indeed create a low area. On a very low crown area over shrinking will put so much stress in a panel, it can eventually buckle the whole panel. I suspect that would take a lot for a shrinkng disc though.

As I said earlier, I have no experience with a shrinking disc but have used an O/A torch for years.

John
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  #174 (permalink)  
Old 04-30-2017, 08:09 PM
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So over shrinking a spot that isn't a BIG dent will cause all these stresses? Well I had little areas with little crown, so does that put me in the buckling a panel group? Again, this large oil-canning dent is near problem area #3. #3 saw the shrinking disc a lot. Could it be all the metal is shrunk towards it and I actually have to stretch metal away from it with the slapper? Do I hammer on or off dolly? On dolly will make it stretch faster, right?


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  #175 (permalink)  
Old 04-30-2017, 08:30 PM
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Wow. You are asking some tuff questions to answer from a picture. If you need to stretch metal use hammer on dolly. If you are shrinking or trying to lower a crown use hammer off dolly technique.

If you have over shrunk a low crown area the repair area will be low. If you have waves or ripples running away from the area it indicates an extreme over shrunk condition. In that situation the metal will try to gather just as if you tried to pinch a sheet of paper in the middle.

You will also find the more you work an area, the harder it gets. The metal actually "work hardens" and becomes less and less malleable.

I have shaped metal as a hobby for years but pugsy has experience with a shrinking disc which I don't. His advice will be better than mine in that area.

John
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  #176 (permalink)  
Old 05-01-2017, 04:14 AM
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Stretching back later is easier than shrinking.

I have gotten oil cans to stop with the disc before usually.

Give it some more, a bit at a time in different spots.
Small bits at different places.

If shrinking doesn't work:
To stretch back, use the slapper on dolly. You'll hear a nice ring sound when doing it right.

But, like I said, make sure your problem is over shrinking and not that it's still stretched too much.

You could try going around the edge of the bubble ringing the slapper on the dolly. You keep checking the bubble as you go.

Again, do a bit, press the bubble and feel for changes. It will talk to you and tell you if it's feeling better.

And remember, don't panic, it will get done.
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  #177 (permalink)  
Old 05-02-2017, 05:17 PM
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I just played with the roof skin again tonight for about 30 mins. I think I'm done with it. I give up. I'll have to buy a new skin. I'm just banging and shrinking with no results. I have no way to know if I'm over shrunk or stretched and therefore can't really proceed with any fix. The benefit of using this one was I knew it fit perfect. The reproduction ones have bad reviews and are notorious for bad fitment. I guess I'll have to tackle that too.

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  #178 (permalink)  
Old 05-02-2017, 05:52 PM
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Are you squirting with water after you warm up the metal with the disc?
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  #179 (permalink)  
Old 05-02-2017, 05:54 PM
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At this point, just go all around the area with the disc and quench. You have nothing to lose. It should only take about 15 minutes to go all around.

Have you been banging it?
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  #180 (permalink)  
Old 05-02-2017, 06:09 PM
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I put water and a little diluted dawn soap in a squirt bottle. I quench with that.

I banged areas I really shrunk down and areas that seemed like they were dented inward/ low but weren't directly part of the areas I worked on. If they were inward I figured that might mean they were over shrunk areas.


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