Aluminum Filler

[Hal]

Hi All,

I am planning on reusing an existing aluminum cow on my project. It is dented in several places. I think that I can remove most of the denting, but I will probably have some depressions and waviness remaining. Does anyone have any experience with using dent filler in this type of application? It seems like a pretty tough environment with all the heat and cold along with flexing. I am looking for specific products that have worked for someone.

Also I would like to hear about successful methods of dent removal. I am not very experienced in aluminum repair.

All advice will be greatly appreciated.

Hal

[Hank Jarrett]

Re: Aluminum Filler

I would NOT use any fillers on your cowl. You need to get some books on "Metal Bumping" and that will introduce you to a whole world of metal forming. I have straightened several cowls (never seen an aluminum cow and don't quite know where one would go on a Taylorcraft). That was an attempt at a joke
Look for the books from places like "Eastwood" and try finding a real "old time" body shop. If you walk in and DON'T smell Bondo, but DO hear lots of people tapping on metal you are in the right place. The old timers there will know the art of tapping out damage instead of filling it.
This could take a whole thread on metal working all by itself but if I had to give ONE piece of advice it would be to NEVER "hit" the metal. Hitting it stretches it. GENTLY PERSUADE it into the shape you want. Have an old metal trash can near to beat the C**P out of when you get frustrated, but DON'T BEAT ON THE COWL. I literally remove dents and damage with the back of an old soup spoon, just "pushing" the dents out. Gentle tapping with a plastic mallet (NEVER hit the aluminum with a metal hammer!) and a dolly on the back side can actually shrink a dent out. Try and find someone to watch. It looks like magic when it is done right. Check with the Hot Rod folks. They usually know where the old time Hot Rod guys are who do real metal work. You DON'T want the "lead sled" guy. He is the one who uses lead solder instead of Bondo. You want the guy who forms a fender from a flat sheet with a shot bag and mallet and finishes it on an English Wheel and a planishing hammer.
When you get started (get something beat up to learn on, not your cowl) I may be able to help advise.
Where do you live?
Hank

[Hank Jarrett]

Re: Aluminum Filler

Where is Cornelius? Are you far from Virginia Beach VA? (just checked your info). I'm really swamped right now but maybe we could get together and look at your cowl. My plane is at SFQ in South East VA.
Hank

[Hal]

Re: Aluminum Filler

Hi Hank,
Thanks for the reply. Sometimes my typing leaves a little to be desired. I don't think that I want to mount a cow either. The plane might come out a little overweight.

I will start asking around about experienced car body guys. I live right in the heart of Nascar country, about 30 miles north of Charlotte.

It is my boot cowl that has the dent problem. The lower cowl is too far gone to fix. It looks like it has about 30 patches on it with cracks still eminating from under some. I am going to have to find a way to make a new one.

I will also look for the books you suggest.
Hal

[Pearson]

Re: Aluminum Filler

Hal,

Can you post a picture of the dent in your boot cowl?

Hank is dead on, in that you do not want to hammer the dent out. But how you remove it depends a great deal on what type of dent it is. Does it have a crease, or a line? If so, does it have dimples/smileys at each end? Or is it just a large depressed area. All of this makes a difference on the best first steps you should take. If the metal has been stretched, as in a serious dent, you will need to shrink the metal back down. That is too complicated to describe in an email and should be done by an experienced metal worker.

Before you do anything take a towel or 3-4 clean shop rags and lay them flat against your cowl. Put your hand over the towel and, without looking at the cowl, run your hand over the entire area. If you look where you are rubbing, your eyes will fool you. Don't look, FEEL where the dents and high spots are. Mark the high spots with a carpenters pencil, or draw a circle around the low spots. For every low spot, there will be at least one and probably more high spots.

If the dents are in an area where the reinforcment channels are on the inside, you MAY need to remove them and reinstall them after you get the dent out. Even if they are bent, you would want to straighten them seperately.

If you can get to the back side of a low spot, and there is no reinforcing channel there, you can push with your thumb, the heel of your hand, or a wadded up cloth while you or someone else VERY lightly taps on the high spots around the dent. Basically all you want to do is BOUNCE the face of the hammer off the high spot. The real force is done on the low spot from the back side. In other words, you may be pushing from the backside in one spot and hammering on a high spot several inches away. You need to use a very lightweight, large faced body hammer. Don't use the heavy kind you find on the $1.99 table at the autoparts store. It has to be light weight. I used to put a single layer of masking tape on the face.

You can use a THIN coat of body filler, but it has restrictions. You can't use it over any kind of seam or crack. Also you can't seat a rivet in Bondo and expect it to hold for very long. Another problem with trying to use filler is if you are trying to sand it down smooth on a large area, the metal will depress as you sand over the filler and you will end up with a hump in the middle. You would not want to use any filler until you had the metal about 99% where it needs to be. If your filler is more than 1/8" thick, you didn't straighten the metal enough. As far as it vibrating off, if you scratch up the surface of the aluminum (never put filler over paint) with 36 grit sandpaper by hand, it will stick forever. Never use a high speed sander, or grinder on aluminum sheet. It will heat up and cause many high spots and distortions. Hand sand only.

I took my nosebowl off last fall and had about a dozen cracks welded up. At the same time I worked a large shallow dent out of the cheek of my lower cowl on one side. I put a thin coat of filler over both areas. By the time I got it all sanded down smooth, you could see through it in most of the area.

[Hal]

Re: Aluminum Filler

Hi Richard,
Thanks for all the info. I can't post a picture right now because I'm on vacation. As I recall, none of the dents were particularly deep or creased. I think that they are all pretty shallow.

Hank,
I just ordered the book "The Key to Metal Bumping". I read a review online at this site: http://www.classicsandperformance.co...albumping.html in case anyone else is interested.

It really amazes me to watch a real metal craftsman work. I watched a guy make an aluminum wingtip with an english wheel and welding torch. I'm looking forward to increasing my small skill set somewhat with this project. I plans-built a Sonex a couple of years ago but it was just cutting, bending, and drilling.

Hal

[Hank Jarrett]

Re: Aluminum Filler

The white plastic hammers from Eastwood are great for working aluminum. A little expensive but here is some good news. I have the expensive ones from them, and a bunch of extras from Harbor Freight. The Harbor Freight plastic hammers are DIRT CHEAP but just as good as the expensive ones. There are straight ones and tapered ones of different diameters. For large shallow dents the biggest diameter ones work best, but the heel of my hand seems to work even better for large areas. You won't hit it too hard with the heel of your hand.
One of my favorite tools is still a metal spoon. You rub the curved surface against the back side of the dent and it just sort of melts away against the buck. Think of the aluminum as being clay and you are pushing it back to shape. The other thing to do is evaluate how the damage happened. Kind of do a slow motion of the damage forming in your mind while you look at it. Start with the first contact point and go step by step to the final appearance thinking about how each fold, peak and dent formed. When you press the damage out, do it in the reverse order. Don't start with the worst spot, start with the last part to form and work to the first.
Hank

[Pearson]

Re: Aluminum Filler

Ditto on what Hank said. Generally speaking, you want to start at the edges of a dent and work your way in. I think you will be surprised at how much you can do with your bare hands. Push on the high spots from outside and push on the low spots from the backside, and you should be able to get almost all of the dent out, as long as there are no creases or stretched metal.

[mulwyk]

Re: Aluminum Filler

I'll second the notion of using your hands to straighten the cowl. I started out using a leather mallet tap, tap, tapping the high spots but when that didn't seem to be getting anywhere I ended up doing the majority of the re-forming with my hands. Around the edges I used a thumbs-on-the-high-spot and fingers behind technique...squeeze, feel the bump, squeeze some more. In center panel areas I used the palms with a wood block behind.

[Hal]

Re: Aluminum Filler

You guys are providing some great advice. I think that I'll dent some scrap aluminum for practice before working on my boot cowl. I'll start with some soft hardware store aluminum and work up to some 6061-t6.
Thanks to everyone,
Hal

[Hank Jarrett]

Re: Aluminum Filler

Put some cheap aluminum flashing on a frame and throw a baseball and some golf balls at it. Gets the frustration out and makes some nasty dents to practice on. When you can push the dents out and the piece of metal will lay flat again with no dent you have reached the master level for dent removal. The next step is to take a flat sheet and wheel it into a hemisphere on the English wheel, followed by working the same piece back to flat enough to lay flat on a piece of glass. I have only seen one or two people who could do it. AMAZING to watch! One of the guys who did it sold English Wheels many years ago. A REAL artist! If the cut edges of the sheet had been straight cuts at the end I would have thought it was a trick.
Hank

[N96337]

Re: Aluminum Filler

Go to www.metalmeet.com and you'll find a whole bunch of guys and gals that can work magic with metal, and they're usually very good about helping others learn.
As far as the boot cowl goes, I'd just put new skin on... it's not too tough. If you do a search on here, there's more than one person that's got pictures showing it being done, if I remember correctly.
John

[Pearson]

Re: Aluminum Filler

If you are going to really get into doing this, and want to try the method where you rub the dent out from the backside, try using several blocks of parafin wax melted together. It self lubricated the backside of the metal and forms itself to the shape. Don't use any kind of grease or oil.

[Hank Jarrett]

Re: Aluminum Filler

Richard,
I haven't tried that. Can you explain the process further? Are you using the parafin as the buck side and pressing into it or spreading parafin over the surface to distribute out the force as you push the bulge down?
I LIKE the idea of something to lube the surface other than an actual "lube". They make a MESS and don't work well, allowing the spoon to sometimes damage the surface.
Hank

[mulwyk]

Re: Aluminum Filler

Hank,
I don't want to practice removing dents or anything but your idea of throwing baseballs at aluminum sounds great! I'm gonna draw a little picture of the local building inspector on the aluminum first. (Hey Scotty-boy inspect this...Whack!!) great therapy, I feel better already.