Metal shrinking question

[wrndln]

I am trying to shrink some spots the front seat tub on my 29 phaeton with a shrinking disc. It looks like someone or actually many people took pleasure kicking the panel from the back seat. It has several large dented areas on the panel. It appears the panel is shrinking a little on the places where the smaller dents and imperfections are, however there are 3 larger areas (see black circles) that pop in when ever it try to shrink them with the disc. I am pretty sure the metal it stretched a fair amount, as I can push the dents in and out like an oil can. Every time I try to put pressure with the shrinking disc, the panel pops in (concave). I can then pop in out from the inside, but it just pops in again when I start to try to shrink it again. Can someone with disc shrinking experience explain what needs to be done to shrink these 8" or 9" circular stretched areas? I have done a fair amount of rust panel patching and other body work, but I certainly haven't mastered metal shrinking. I wish I knew more about it. I have watched several videos and read a book from Frank T Sargent about metal shrinking, but I still don't have it down. Thanks in advance for any help with this question.
Rusty Nelson

[Ross/Kzoo]

What I did was to shrink on the "high" side. Heating the metal with the shrinking disc and immediately putting a cool, wet rag on the surface. I don't have a lot of experience with this but it worked for me. I hope others chime in.

[d.j. moordigian]

Rusty,

Are you shrinking from both sides? I would do the back side(seat side) on the
3 big ones.

[wrndln]

Whichever side I try to shrink, the metal pops out to the other side. Do you just try to shrink the concave metal when it pops in?
Rusty

[d.j. moordigian]

Originally Posted by wrndln

Whichever side I try to shrink, the metal pops out to the other side. Do you just try to shrink the concave metal when it pops in?
Rusty

I would be doing the convex, not the concave....you can't get at the
center..if concave...right?

[wrndln]

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What I am try to say is I CAN'T do the convex side, because as soon as I try it turns into the concave side. I would get dizzy trying to go from one side to the other as the metal quickly pops out to the other side when I put a little pressure with the disc on it.
Rusty

[d.j. moordigian]

This is why we talk on the phone....LOL

[PeteVS]

Have you tried putting something behind the area you're trying to shrink to keep it from popping back in? Maybe supporting the panel on a table with a block of something under the raised area and holding the rest of the panel down?

[Richard Wilson]

Have you tried an acetylene torch? Shrinking hammer and dolly?

[QGolden]

Are you shrinking the right spot? Sometimes a damaged spot adjacent to the oil can dent can put pressure on the oil canned area. Did you try shrinking from the outside of the stretched area, working towards the middle?

[59mgaguy]

You should be able to bring the 8 and 9 inch dents down to a smaller size with a hammer and dolly.

I see the picture of your buffer but not of the shrinking disk.

[Kevin in NJ]

What is the rpm of your grinder?

You must have a high speed sander/ grinder. A low speed sander will not work.

The shrinking disk will not easily move creases. You would have to do hammer on dolly work to get the metal flat first. Then the shrinking disk will help you bring down the high metal. You may have to pick areas high then shrink them.

The shrinking disk works by rapidly heating the high spots. Take your knuckles and run them across the carpet and you burn the tips of them. Flatten your hand and you will not get the burns.

It will take a while to get your panel flat. It helps to do some reading on metal work. You will find some hints at my website.

[wrndln]

My grinder is a Craftsman heavy duty two speed 3600 and 4600 RPMs. Like I said it is heavy, not one of the Harbor Frieght light weight machines. It is probably 25 or 30 years old, but hasn't been used much. I have it set on high speed for shrinking. I thought 4600 RPMs was enough to shrink sheetmetal. I suspect 19 ga metal is harder to shrink than the thin stuff on cars now-a-days. I used the disc on the worst spot for 15 minutes off and on and could see no difference - it still oil cans, which I think means it is still stretched. The wet rag does steam a little, but not the sizzle I would expect. I am about to take my tub to a professional auto body shop that has shrinking experience with older cars, not the Bondo sculpturers like most shops today. I don't want to mess up the original tub.
Rusty

[road_king]

I got my small and large shrinking discs from Wolfes Metal Fab. They have a video that may help https://www.youtube.com/watch?v=X8cruauERmI,, also the old book "The Key to Metal Bumping" may help you understand the dynamics of whats happening with the metal. Both things helped me with work on my panels, good luck.

[Ross/Kzoo]

You definitely have to work with shrinking wheel to get a lot of heat into it. Hold the shrinking flat to the surface to create the max. heat. You don't need to bear down on it just build the heat up.

[BRENT in 10-uh-C]

Rusty, pictures can always be deceiving but it appears you are trying to shrink WAY before it is time to shrink. To me, it looks like the metal is still "crumpled". If this is the case, then all the wrinkles must be removed by planishing. That will be done with a hammer & dolly. Once that is done, there will be excess (stretched) metal from the repaired trauma. (Usually you will find the metal is 'oil canning' at this point). That is the time where shrinking is needed. The way to tell if the shrinking disc is spinning fast enough is if it will get a piece of sheetmetal hot enough to make a blue spot. Personaly, I think your disc is being abused as it appears the stainless is turning blue, ...which if that is the case, it is spinning fast enough. Also, I would not use a torch until the disc is unable to get into a corner simply because the disc is much more controlable.






.

[Kevin in NJ]

Crumples mean it is shrunk.

Take a piece of paper and crumple it up and then flatten it out and compare to a flat sheet. It will be smaller.

If you shrink before it you need, then you will make the oil can worse. Shrinking is only a last resort after you are sure that is what is needed. If you do not know when it is needed then you are not ready to shrink. You need to take some time to learn more. I give this advice because I shrunk on advice of a local 'expert' and made a panel worse. I later learned I needed to stretch to fix the problem.

[BRENT in 10-uh-C]

Originally Posted by Kevin in NJ

Crumples mean it is shrunk.

Take a piece of paper and crumple it up and then flatten it out and compare to a flat sheet. It will be smaller.

If you shrink before it you need, then you will make the oil can worse. Shrinking is only a last resort after you are sure that is what is needed. If you do not know when it is needed then you are not ready to shrink. You need to take some time to learn more. I give this advice because I shrunk on advice of a local 'expert' and made a panel worse. I later learned I needed to stretch to fix the problem.

That is not my opinion, Crumples mean the metal has only been rearranged.

Think about what you said. Using your example, taking a piece of (flat) paper and wad it up until it is crumpled, you are correct in that it will be smaller, ...simply because the shape of the paper has been rearranged. To remove the crumples, the sheet of paper must be flattened in some manner. In other words planished. Once planished, the size will return as original. Shrinking is NOT going to make it return the original size or shape.

.

[dave in australia]

Some good advice here;

http://www.metalshapers.org/tips/covell/

http://metalshapers.org/

[lotuselan36]

My heck, let's beat a dead horse. Read Sargent's book and pay attention to his statements on what happens to metal when it is damaged. Take that shrinking disc and skip it on a lake.