Anyone knowthe best procedure to shrinking metak with a torch and wet rag. I have tried it and have had some problems. school me on this please
Only heat a spot the size of a dime, no bigger. Lightly tap the center once with a high crown body hammer, and then cool with a wet rag. Repeat the process at least an inch away from the original shrink if you need to. It also helps to have a slapping file to finish tightening and evening the area. The least amount of heat put into the panel, the better. Hope this helps. blackwolfhollow
It also helps to hammer on dolly in a circle around your heated spot to shrink and then tap the center. Then refer to the above post.
Hey, Yeah, the idea behind the circular pattern, when striking the heated metal ,is to force the thicker metal from around the edge of the stretched area into the center (heated spot) which is much thinner, and thus stretched. The wet rag is used to speed the process and to draw the metal from the surounding area into the center. Too much heat, not enough hammer/dolly work properly directed, to much hammering on already stretched metal and the poor use of a wet rag, over to hot a metal area, will all cause more damage than they will repair. Always hot shrink with serious caution, and make sure the metal you are attempting to shrink is actually stretched, and not just metal that hasen't been properly bumped out first! S****ey devils C.C. "Meanwhile, back aboard The Tainted Pork"
I like to tease the streched area a little. With the torch about 8 to 10 inches away I'll circle the the streched area in a 3or 4 in. circle. Watch the metal close and when you see the area push out, Spiral in close and quickly heat a dime size spot red. (If the metal moves in, stop and bump it out) Hand the torch off to your Grunt and using a toe dolly, hammer one or two good licks to the red spot to force it back where it belongs. Then hammer/dolly in spiral around the area to flatten. Do this all as quickly as possible and then I quench with a rag from a bucket of cold water. Wipe it dry and check for tight and straight. work the metal a little cold. Repeat as neaded until you like it. On old cars with lots of crown, you can pop hail dents with this method and not hammer. Heat,Splash,File, Grind
Here's a vid I saw on YouTube. No hammerwork but it shows you the basic principle.. Fire & Water http://www.youtube.com/watch?v=mptiiRLEJs0
Heat is often enough to do the shrinking. Quenching can be optional as well. I use a propane torch and barely heat the metal to the point of discoloration, never going to red hot. Sometimes I quench with a wet rag, sometimes not. Depends on whether I need to shrink a large area or not. In fact, I usually defer to the shrinking disk over a torch these days. Tim D.
I've had varying results with quenching after heating. So unless it's a very small area, I don't do it. Here's what works best for me. Using a rosebud tip (yep, the big boy!), blacken the area to be shrunk with an acetylene flame. Now turn the heat up and add some oxygen. KEEP YOUR TORCH MOVING and about 8 to 12 inches from the surface, your objective with this technique isn't turn the metal red hot or even close to it. Rather, you're going to gently heat the area until the soot just barely burns off. This happens at about 400 degrees if memory serves. At this temp, the molecular structure of the steel is not changed, but it's "loosened up" sufficiently to allow you to easily hammer and dolly the stretched area back into shape. On large areas, sometimes I'll use a big wooden mallet and a 2x4 as a dolly. Wear insulated gloves, it's hot! I find I have much more control with this technique and it works really well for reworking large areas like bedsides, tailgates, dented roofs and doorskins.
thats a totally different process than shrinking. What you are describing is annealing. While very helpful sometimes it is not a good technique for an overstretched portion of the metal.
if your shrinking some high spots (the bumps from dolley work ) invest in a shrinking disc they work great
Yes, maybe I should have clarified that a bit more. It's not the same thing. Why would you consider it to not be a good technique? It's always worked great for me, I just did a set of bedsides that were bowed, stretched and dented all to hell. The shrinking is done by your hammering, not the actual heat of the torch.
Guys I realize this is about heat shrinking, but what about the other kind of heat shrinking.....the shrinking disc? If I shrink with a torch I have problems contolling the shrink (and the area)-if I use a Shrinking Disc it shrinks the highest point, it is a little slower than a torch but so much more controllable. In fact, there are some people who have used it to shape panels (which, to me, seems like it would take a long time). When I started banging Metal I would Hammer on Dolly and get too many "highs"-I could put the Disc on it and the high spots would turn blue (you aren't supposed to let it turn blue though), and then quench, re-heat, quench, and so on-on my last p*** with the Disc there would be no "highs" and you could actually see the Metal relax and lose the work hardening. With a little practice you could almost metal finish with it. For most of us rookies a shrinking disc is a match made in heaven-it's slow, controllable, and if you shrink too much you can re-stretch it and shrink it back down-
It sometimes helps to use a shrinking hammer (the one with the toothed face) or slap it with a toothed slapping file. Don't try to move the metal as much as tighting it if it's a large area if that makes sense. It's real easy to over do it. Once the metal is tight then you can slowly bump it out where it needs to go. Shriking discs are a lot easier and safer (for the metal) in most cases for beginers.
I'm with Tim...Heat shrinks without the use of a hammer and without getting the panel any hotter than it needs to be to steam when quenched. This is well below the temperature of any color change... at least very noticeable color change. You can shrink many times in the same spot if you do not overheat it. A torch will work great with just a little quenching. Hammer and dolly work is better done before and/or after the panel is shrunk and cooled in order to smooth where necessary. If you use a small tip and heat briefly until the metal swells a tiny bit, or just starts to change color, you will shrink controlably. A shrinking disc is more controlable than a torch because the heat is focused mainly on the high areas. Video demo at the bottom of this page en***led simple dent repair: http://metalshapers.org/101/index.shtml John www.ghiaspecialties.com
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