Metal Shrinking Pics and Stuff

Curt Campbell

Curt Campbell

Senior Member
I know shrinking metal is kind of a mystery to some folks. Shrinking 18 or 19 guage metal on a Model A is one thing, doing it on todays flimsy-assed metal is yet another...but effective if careful. The following pics show a car I am working on....quarter panels were both buckled pretty bad from pulling the rear out some on a frame machine. If the panel is removable, I just replace it...cheaper...but quarter panels are a pain to change. I have used my stud gun to heat small spots then immediately cool the spot with a wet washcloth ( I have a shrinking tip for the gun). It works like a charm. In this case, the result of using studs and shrinking the panel is a straight panel needing only some thin coat of glaze putty to finish the repair. Using a torch or shrinking disk on an A you can make an amazing difference in the panel. Patience is necessary of course.....

I was shrinking metal before shrinking was cool.... :D
 

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Curt,
That is exactly what I am hoping to do. I have a Harbor Freight stud gun I was hoping to use to shrink metal on some panels on my car. I have never tried shrinking with a stud gun before. The gun in the picture looks like a HF tool. Did you just use a regular stud tip or find a tip that is just for shrinking? Also, how long did it take you to learn how long to trigger the gun so as not to burn through the metal or not do any meaningful shrinking? Could I send you a PM to maybe get some additional information on how you use the gun?
Rusty Nelson
 
wrndln said:
Curt,
That is exactly what I am hoping to do. I have a Harbor Freight stud gun I was hoping to use to shrink metal on some panels on my car. I have never tried shrinking with a stud gun before. The gun in the picture looks like a HF tool. Did you just use a regular stud tip or find a tip that is just for shrinking? Also, how long did it take you to learn how long to trigger the gun so as not to burn through the metal or not do any meaningful shrinking? Could I send you a PM to maybe get some additional information on how you use the gun?
Rusty Nelson
Click to expand...

I got a shrinking tip for my HF stud gun from Eastwood. It was ten bucks or so. It is just a big rounded tip, of course without a hole in the center.

Doug
 
Mine is an H and S Body Spot....not harbor freight. The shrinking tips are available...9 bucks for two different ones. I have just used the regular tip but works better with correct tip. PM me anytime or email
 
I remove the gun as soon as I see it turning red on the thin modern metal....not so critical on the A metal. I also IMMEDIATELY place the wet towel on it....it sizzles. I dont think u will have a problem burning thru with the gun.
 
Chuck Sea/Tac said:
Why do you need the gun A's opposed to using
acetylene? Better heat control?
Chuck
Click to expand...

You can use an oxy/acetylene torch providing the tip is small enough to concentrate on the specific area and not have the flame's fan spread out over a larger area.

My question is more why do folks get the metal red hot? Metalmen smarter than me say this is detrimental to the process as it makes the metal harder in that specific area.
 
I agree with Brent on this one. Getting the metal red hot has not been a good thing for me. I do NOT know what causes it, but welding in areas that have been red hot seems to make the metal lose some of its ductility.

I am absolutely a HUGE fan of the shrinking disc. The other methods heat the entire area inclusive of the perimeter of application, whereas the shrinking disc hits only the high spots (to a slightly blue hue). Spraying with a water mist provides a small amount of steam if heated to the correct temperature, and only the high spots will shrink. If you have a severely wrinkled area, alternate from front to back and you will be amazed at how quickly the metal will flatten out.

I have seen areas done with the 'spot' method distort disproportionally when welding both on and near the 'spots'. I am also NOT a good bodyman, so it might be that I do not know how to do these 'spot' types of shrinking, but in any event the shrinking disc is MUCH faster from my perspective, but not applicable in all scenarios (like the example Curt shows, if the panel is not close to flat).

I attended a metal shapers event and when I saw an example of where the stretch was inward, I asked the guy with the shrinking disc how he was going to 'fix' that. His response was to use a hammer and knock the dent OUT, then proceeded to use the shrinking disc to smooth it back IN. It worked well and was quick.
 
Here are some comments on shrinking to keep in mind.

Shrinking is a much misused body technique.

You must first understand why the panel is in the state it is in before you try to correct the problem. For example, a wrinkled panel on a curve may appear to have a stretched area. When the real problem is shrink at either end of the curve. I mention this because when I first started on my metal working adventure I got some oil cans after welding a patch in place. A body guy with 40 years experience told me to shrink the oil can. So after chasing the oil can around the panel I gave up. I succeeded just making the whole panel smaller and never able to be properly repaired.

I got my eyes opened by reading some and watching some metal working videos that are now available from smartflix.com. Shrinking magic was one video and some others on rebuilding a fender.

What I have learned, mostly the hard way.
Heat shrinking is only done as a last resort after I figured out the cause of the issue in the panel. Many problems are really a shrunk area that needs stretching.

Go slow and cautiously, especially when you are just learning. Do one or two small spots. If you think you need a lot of shrink work the spot with hammer on dolly. Otherwise, let it cool on its own for a while. Do not use a wet rag!!! That is bad advice! Once the spot has cooled down past the plastic stage then use a wet rag to cool the metal. Now the HARD part. You MUST wait until the panel has equalized in temp before evaluating. If that area is still warm then the metal will still be too big and appear to need more shrinking. Walk away for a while.

Metal starts shrinking when you see it turn blue. It does not have to be red.

A shrinking disk with the proper speed sander is your best friend. You can level quite a bit with one.

In the end, I spent a lot of time combing through a lot of information. Both online (there is quite a bit out there) and through videos you can now economically rent (I spent $$$ for the videos). Metal working goes way easier once you over come lots of bad word of mouth info and you learn to be patient.

Yes, I am encouraging you to rent some videos and poke around the web and learn (or relearn) some new techniques. It is quite satisfying actually making the metal do what you want and end up barely needing to level a panel with fillers.
 
I agree with not overheating...no need to. The old rule of thumb I have been told is if your wet rag sizzles just a little bit it was heated enough. I do use a torch or disk on thicker metal such as on an A. The shrinking is most useful after any metal bumping or straightening has been done...or to repair oil canning effect. I have a very small heating tip for the torch.

Shrinking is only one several methods to straighten metal....and only if stretching has occurred.

Best rule of thumb is be careful not to overheat! Heck, the modern rice burners I rebuild start warping if I even push the oxygen\acetalyn torch cart past them!!!!
 
Kevin and Brent: you guys advice is always spot on!! Thank you for taking the time to post helpful information for the rest if us......
 
I have had good success with a shrinking tip on a stud gun. I place the panel on my steel workbench with the raised area in contact with the bench, and then zap it quickly at the high spot from the other side, and then do a bit of hammer work as it cools. I do not quench the metal with water. It seems the weight of the panel helps push the metal back in its right place. Smoothing out metal this way is a slow process and the panel needs to be off the body. With more complex metal shapes I have sometimes used a small plate of steel as my backup. I am a novice but this method has worked for me without over shrinking panels.
 
Brent, what kind of rpm do you use with the shrinking disc. i've been trying to use one on my electric buffer but i don't think it's got enough rpm to get the metal hot.

Russ b, my brother in law uses his stud gun to shrink metal in the same fashion. he heats up a small spot and then uses a hammer dolly working around the hot spot in a circle fashion working in toward the heated area, kinda pushing the metal into the heated area.

Scott
 
The shrinking disk needs to run up in the 6000 rpm range.

A buffer only gets to 3000 rpm and that does not work.

The slower speed does not heat up the tops of the bumps rapidly. Instead you end up heating the whole area and the high spots do not shrink.
 
Last week we completed the fabrication of a power shrinker that I designed to get into smaller and or deeper areas that need to be shrunk where the shrinking disc was not applicable.

I was getting tired of not having a machine that would get further into a panel that required shrinking. I had modified a Marchant air powered shrinker, but they only have a throat depth of 5-6 inches and NO 'post height', so I figured out this machine to provide a lot more depth and an angled lower post to allow for reaching up into a fender or a contoured panel.

It is quite heavy and is only useable if the panel is off the car and can be hand held, but it worked great the first time we used it. I purchased a set of Eckold shrinking dies from overseas that have the newer, and deeper stipling design that provides a deeper grip. It does leave a very slight stipling pattern, but so far I have been able to sand down to remove them. Because the metal has been shrunk, it is thicker, and even after sanding the panel is thicker that when I started.

We have not got around to painting it yet, and might not paint it as my shop seems to be getting an 'old-timey' look fromall the hand made 'stuff'.

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It definitely came out nice. I followed the build and discussion on Kerry's forum and I think it awesome.

One of these days I expect to see the 3 containers being moved out with the little goats so you can add another 20' of width to the south side of your shop just to house all these new tools! ;) Oh, and Deron & Dan Shady need to look out 'cuz you are rapidly approaching as many cool tools as they have in their shop!! :D
 
Brent, you need to bring Jimmy and come over one day to try these things out.

I built this last one to get into places that the foot powered kick shrinkers cannot reach. The early ones had the marchant style dies that were wider than deep and were in frames that only allowed between 5" and 7" deep with no 'post' capacity.

We have discussed why I am such a fan of shrinking as opposed to the hammer and stretch method of panel repair, and this just seemed like the next logical progression. It has a much deeper throat and a tapered post similar to Kerry's english wheel design. I did this to get up and inside the deeper sections of the Model A fenders and some of the aluminum panels that I making for the speedster. It does require that the panel be hand held to use. I got hit on pit road so many times it is becoming uncomfortable for me to stand on one leg for very long and operate the kick shrinker is why I put a motor on it.

The Eckold dies are the newer style that has the deeper stipling and it works great with little pressure. It often leaves a small stiple pattern on the alumunim panels, but it sands down quite readily. Because the shrinking thickens the metal, I still have a thicker than original panel, even after the sanding. I like that because it makes the welding somewhat easier, minimizes stress inducers and is less likely to work harden when shaping.

It has a two horsepower motor that I got from a salvage yard and based on 3 foot pounds of torque per horsepower, I calculated that the post pressure on this machine is about 22,400 psi and am guessing that with the 40mm die set that I am generating close to 18,000 psi gripping pressure. The smaller of the Eckold machines generate almost 38,000 psi but they are made to use the larger 60mm and 80mm die sets.

We need to figure out how to have a mini metal meet in this area of the country, similar to the ones that you had at your shop. I miss those and had a great time attending them. If I had a larger shop, I would like to have one here, but the machines are taking up a lot of space, especially the power hammer as it consumes a large operating room foot print.
 
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