heat to remove a dent???

What do you think about using heat from a small torch, not just a heat gun, to remove a little dent, or wrinkle out of the aluminum skin? I have a small dent that I did hammer out carefully until almost flat, but you can still see the aluminum is not perfectly the way it was. I've read about heat shrinking skins. Can I use a little propane torch and get the aluminum to shrink back into perfect shape? I'm inclined to "get over it" and move on. But a car guy told me that heat and a little tapping should make it perfect again.

It could also burn through, or actually make a larger dimple. I'd move on, as these dents are easy to fill and paint over. But, you can always practice on scrap.

L.Adamson -- RV6A

dont do it. you will certainly change the heat treat of the material. move on and rethink it in 6 months. i promise it wont seem like much of a concern then. IMHO i would say it would be a mistake to try it. YMMV

L.Adamson said:

It could also burn through, or actually make a larger dimple. I'd move on, as these dents are easy to fill and paint over. But, you can always practice on scrap.

L.Adamson -- RV6A

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cytoxin said:

dont do it. you will certainly change the heat treat of the material. move on and rethink it in 6 months. i promise it wont seem like much of a concern then. IMHO i would say it would be a mistake to try it. YMMV

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I agree with the advice so far... and by the way, heat wont shrink the skin, it makes it expand (just like any other metal).
Also, hammering on a dent or wrinkle is not the nest way to remove it. It can caused localized thinning and stretching which makes the skin fit even worse. Not that it shouldn't ever be done, but it must only be done in very specific situations and even then be done very carefully.

sglynn said:

What do you think about using heat from a small torch, not just a heat gun, to remove a little dent, or wrinkle out of the aluminum skin? I have a small dent that I did hammer out carefully until almost flat, but you can still see the aluminum is not perfectly the way it was. I've read about heat shrinking skins. Can I use a little propane torch and get the aluminum to shrink back into perfect shape? I'm inclined to "get over it" and move on. But a car guy told me that heat and a little tapping should make it perfect again.

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I've never heard of using heat to get rid of a dent but I have used ice to get rid of dimples left by hail. Takes a hot day, a little ice and a bit of time but it works. Park in the sun and let the skin heat up ten hold the ice in the middle of the dimple, repeat as needed or until your hand is cold enough that you decide you can live with the dent. Dry ice works better but a lot more caution is needed.

You didn't say where the dent was. Mine was on the hood and roof of pick-up trucks.

sglynn said:

But a car guy told me that heat and a little tapping should make it perfect again.

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Please don't take this the wrong way, but I would advise you to be very suspect of advice from "car guys", "boat guys", and even "airplane guys". If I had a buck for every time I took somebody's lame advice and had it go completely pear shaped on me, I'd be flying one of them John Travolta planes by now. Walk into any Home Depot and ask a technical question of the first kid that walks up. It's very important that you give the impression that you know absolutely nothing. This'll really embolden the guy to let the b.s. fly. All you're getting is an inaccurate recitation of all the lame advice that he's heard over the years and NO first hand knowledge.

A few weeks ago I got to listen to a self-proclaimed car expert explain to me how a completely worn out auto paint job could be made like-new by simply shooting it with a couple coats of clear. No prep, no scuff, no nothing. Said he's heard of lots of guys doing it. Never mind that the old paint had huge areas of old clearcoat flaking off and that the exposed color was chalky. The new clear will magically fix it all! Ridiculous.

There are guys (and gals) on this forum whose knowledge and level of craftsmanship is downright amazing and you can sometimes spot them doing crazy things like carving their own props. Find out who they are and take their advice. Regarding your dent, I say move on and fill it before paint. It'll be such a tiny part of the ridiculously laborious paint process you'll actually barely notice.

I'm a "car guy" (proud of it too) and know exactly where his advice is coming from. On older cars the body panels will stretch and oil can. One of the ways to fix it is to use a propane torch to heat a small spot up and then set ice on the spot to cool it quickly. The metal will shrink slightly and if you did it right the oil can will be gone. Works great for an old car roof.

There's no way I'd do it on an airplane though. For the most part car skin isn't structural and screwing with the metallurgical properties isn't going to come back to bite you.

all you will likely end up doing is causing it to oil can. Hammering thins the metal and this cause it to expand, leading to an oil can condition. then you have to use a serrated faced hamer to shrink it and theres no way that can be good for a stressed skin. let it ride and fill it later. as undulated as these things are it highly unlikley anyone will ever notice.

I agree on NEVER heating aircraft aluminum and that hammering is iffy at best. Since you have already hammered this area, it probably won't work, but the "paintless dent removal" method will work on AL without side effects. I'm not good at it, but I did use it on several dents and it works! My Lab put five toenail marks in my rudder just before I was going to close the trailing edge. Took 'em out perfectly! Search on it if you want to try it. Practice on scrap and you won't screw anything up. Pretty easy, really.

Bob Kelly

heating AL skin or hammering

Sorry to say this but you have already messed up by hammering the dent out.

Heating the metal is taboo. It anneals the material and causes it to loose its physical properties and hammering out the dent work hardens the material making it brittle. You should have a copy of AC 43 if you built your airplane and if you don't have one, get it and read it. Airplanes and their repair and maintenance is not a matter to take lightly. It is not the same as working on your car.



C. Murphy former sheet metal mech for a major airline.

thanks for advice on dent removal

Thanks for your replies and advice on dent removal. Conclusion is, I'm moving on and if it bugs me at paint time, I'll fill it. It is small, only a builder would notice it and by using the lead bag behind, and with light taps I was able to make it fairly smooth. It is on leading edge of tank. So on to installing the baffles. thanks

thanks for replys

Conclusion, I'm moving on. The dent is very small (dime size). Only a builder can even see it. I appreciate your replies. Thanks

Christopher, perhaps you missed the question. Annealing, hammering are metal forming process, including aircraft aluminum. But there are details to when and how it can be done. Those details and experiences would be valueable to post. Judgements, not so valueable.

Steve,

Clear as mud now, right?

Unless you've got a real expert -- as in, done it themselves many times -- looking at your specific problem, there's not much point in asking. Everybody means well, but I think they've all got different ideas about what your dent looks like and just how much hammering we're talking about. Incidently, there will be times on the build where a hammer is just what the doctor ordered: putting on a prop extension, bending longerons, bending tank attachments, etc. Also, I would suggest that every time I use my C-frame dimpler I'm hammering skin material a little.

Keep in mind though that common sense says that the only way to create a dent in a flat piece of aluminum is to stretch it a little. Hammering will only thin it, thereby creating more surface where you actually want less. Speaking as somebody who has been working on his project for a VERY long time, rest assured that this little ding will fade in your memory and can easily be covered before paint.

sglynn said:

Annealing, hammering are metal forming process, including aircraft aluminum.

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right you are. a lot of less finished kits require a lot of hammering, forming shrinking and stretching. sounds like you'll likely be good to go in your decision. good luck on your build.

heating dents

Thanks for your notes. Here is photo. It is easy to live with. I used a method described in this forum on a thread named "turning an outie into a dent".

You can hardly see it! I gave up being anal a year ago! It was driving me crazy. You will be amazed on how many dings you get putting the plane together and testing it.

Steve,
If you have access to the backside, and if you have a good selection of dollies (or you're willing to grind a dolly to contour), and if you intend to polish.....

Shrinking and stretching are not that hard. Everything revolves around understanding a basic concept. To stretch, you hit "on-dolly". To shrink, you hit "off-dolly". Not hard to tell the difference; if the dolly rings when you bump, you're on-dolly. If the bump sounds dead, you're off-dolly.

From there it is pretty much a question of selecting the right tools to fit the physical situation. The shape of the part and the degree of access to both sides are the wild cards. In this case the dolly must match the contour very closely. I'd probably use a slapper rather than a hammer.

Soft material (1100, 3003, 5052-0) works easily. Tempered 2024-T3 material makes this job much more difficult. You can use heat with non-structural aluminum parts, but that's not the case here.

If you choose to pursue the matter further, do not work this skin any further until you play with some scrap, same material, same thickness. Knock a similar dent in the scrap and practice.

Having said all that, if you're going to paint the airplane just take a round face hammer and knock it back to an "in" dent, then fill it before you paint.

don't hammer your skin

If the dent is small and the material is not cracked and has good radius just fill the dent and paint it.

DO NOT HAMMER out a dent. It was worked one direction when it was dented and if you hanmmer it out you have worked it the other direction. You now have a weakness and a crack waiting to happen.

Please Please Please adhear to sound practices when working onyour airplane.

Never heat up heat treated alumimun unless you can restore it to its proper temper and don't work harden your skin material by hammering it. Its not the same as bending your longerons. Would you bend them back and forth? I hope not. That is what you have done when you hammer out a dent.

Chris Murphy A&P and former lead sheet metal mech for a major airline.