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MG MGA - shrinking aluminium doors
| I'm doing a complete nut and bolt restoration on a 60 A coupe. One of the doors was badly dented many years ago and hammered out too much so it's now too bowed outwards. I need to shrink the door skin to reduce the bow by about 1/4 ". Any advice from those who have been there before. The entire door skin needs to shrink at the middle by 1/4". Hopefully Andy |
| Andy Preston |
| Andy, I recommend an old panel beater for this idea, there are ways of shrinking metal. Seems like I saw something that Eastwood carried to help shrink metal. A rotating disc on a drill was used in the demonstration. Take a look in their catalog. |
| MWhitt |
| Doors are fairly cheap. You could just replace them with better ones. Sorry I can't help on the metalwork aspect. |
| Steve Simmons |
| Andy When I did a body refinishing course I was told by the instructor to be extremely careful with aluminum skins as they a nigh on impossible to shrink. I think your best bet may be to get it re-skinned. Steve |
| Steve Gyles |
| You could try heat shrinking it. http://www.bodyshopbusiness.com/bb/bb20650.htm and then buy a new door skin!! |
| Malcolm Asquith |
| I had my Mga Coupe engine cover re-skinned by an old time panel beater. He had me but a sheet of aluminium (4x8 @ $75.00) and then using a hammer and a very large dolly proceeded to shape ...form and fit a new shin on my frame. It took him a half a day to complete the total job and it was a perfect fit to the car. At his price and quality of work,I would advise grinding off the old door skin and having a professional install a new one. Gordon |
| Gordon Harrison |
| One suggestion made to me many years ago was to seek out a large-truck body shop. Many of these use aluminum skinned panels. These shops routinely work with the aluminum so should be rather experienced in the art. I never had the occasion to need this, so I do not know how accurate the story is. Just thought I'd share it. It makes some sense to me. Chuck |
| Chuck Schaefer |
| Andy, How much are you talking? I was able to shrink my door skins the old fashioned way by heating localized spots very quickly with a neutral oxyacetelyne flame followed by immediate rapid cooling with a water saturated towel. The challenge with aluminum is knowing when it's hot enough without melting a hole. Speed is essential because aluminum conducts heat so much better than steel. A second set of hands helps here. Mine were stove in about an inch. My goal was to raise them to within a quarter inch of perfect for a skim coat of Rage Filler. BOL, Doug |
| D Sjostrom |
| Dont know if this is the aproved method,but it works for me.After the paint is stripped off use a air cut off wheel, thin blade and cut an X in the panel the extent of the bow. Have a helper press on the panel with a very thin sheet of indoor paneling.When you have gotten the door skin a bit low then tack weld from inside,check your work,if OK then finish welding.Skim coat from there,etc etc. |
| wc wolcott |
| Hi Andy. I have never tried this, but I understand you can purchase a body tool called a shrinking hammer. It has a cross hatched and deeply textured head. When you hit the shett metal with it, (backed by a dolly,) it creates shallow dimples in the sheet metal, effectively shrinking it. Apparently this tool works well and is commonly used by pro body men. You might check with a local body shop for more information. Cheers, Glenn |
| Glenn |
| If you want to do it yourself, the best how-to advice on forming aluminum is available from Kent White's website. He sells books and videos which explain how to do all kinds of shrinking and complex forming. FWIW, he doesn't recommend the textured "shrinking" hammers and dollies sold by various sources. http://www.tinmantech.com/ |
| Del Rawlins |
| The piece Malcolm linked is pretty good, but I could quibble with a couple of points, and in any event it is not necessary or desireable to use heat in many cases.A particular point on the A door is that the panel may be stretched lengthwise, due to the relatively rigid door frame; but not stretched along the vertical line, since the curve at the top gives a lot of flex this way. The heat shrink as described in the article is non directional, not the best choice in such a case. I recently posted the following to a Rover mailing list, in response to questions about repairing the alloy bonnet (punched in the nose and buckled/twisted); a little long, but it is the essence of all collision repair. The shrinking disc mentioned by MWhitt is not likely to work on aluminum. WCW's method is fine in extreme cases, but a bit much for this. The damage you describe should be repairable by someone who knows what they are doing, BUT, if they don't KNOW, they will screw it up to the point of not being salvageable at all. I have repaired this damage as follows. The rule is that damage must be removed in the opposite sequence to how it was produced. Whatever caused the nose ding pushed the edge back, giving a large bulge in the top, and resulting in the buckle in the little ridge on the top panel. Look at the panel from all directions with a single light source moved around at a low vision angle to see where the distortions are. If any attempt is made to flatten the buckle without pulling the edge forward, the entire panel will distort and no amount of fiddling will fix it. If a method to apply a constant pull on the bonnet edge can be arranged*, you will see the bulge reduce; then, it is entirely possible that ONE well applied hammer blow with a dolly underneath will unlock the buckle in the face panel ridge. It will be a very gentle blow with the correct shaped hammer. There is almost certainly a corresponding buckle in the bonnet side edge at the little rubber bumper hole, and a bit of bending in the X support, both of which can also be straightened with the forward pull still in effect. The ding itself probably affects an area no more than 4" across. Drilling a few 1/4 holes in the support structure can allow the gentle application of small shaped punches to work out the ding. I have been known to make a half dozen punches with different end shapes and bends to work out similar dings. Again the repair procedes opposite to the damage - outside first, then work toward the center. *To pull, you will likely have to make a shaped wood block to fit under the bonnet edge, and possibly a matching shaped piece for the outside so you can clamp them together. You do not want to put stress-locking dents in the inner support structure, as they may lock the damage into permanence, even though you can't see them when all is done. The C-clamps used here are a good thing to pull on. Then arrange a comealong to the garage rafters so you can pull with the bonnet open (and the handbrake on with wheels blocked), and pull on the wood - Gently! - while the bonnet is free to align itself with the pull. Some of the best panel men in the world are in SoCal, the following links should help to find one: http://www.metalshapers.org/ http://www.tinmantech.com/html/kent_white.html http://www.metalmeet.com/ While Paul's comments about shrinking are true, you do not need any shrinking now, and will not if someone doesn't attack the thing in the wrong way. Minor amounts of shrinking can be done cold in any event, and if heating is resorted to, much danger results. It is very easy to melt the aluminum into a useless puddle, and even if successful, the metal will be mush soft unless it is overshrunk and then cold worked back to a reasonable hard condition. NEVER hammer on hot aluminum - it is "hot short" which means it cracks or crumbles if hit hot. No nails, studs, or holes, should be used on any panel unless you are looking for a crappy bondo finished job, or know how to weld and cold finish the results, in which case you would know how to do it without them. If by "shrinking hammer" Paul means any of those with teeth, or swirls and cam mechanisms, I would say that the only legitimate use of such is to beat senseless the guy who sells them - they do evil damage to the metal. FRM ********* Agree with comments about going gently and working it out as you said. By shrinking hammer I meant one with a grid pattern on it, possibly "teeth" as you define. For thin Al yes it would be too severe. The shrink is only the Last step, to help fix the ding. I have seen the Al shrink done so I know it works. PVS ********** Yes, that's the booger. It's nasty for metal, induces vicious stress points, and makes it impossible to metal finish. Yes, it works, but it is totally unnecessary, and is only a fix for the incompetent and impatient; the only useful function is to convey cash to the purveyor. People have been "raising" gold, silver, copper, steel, or aluminum for thousands of years without such, and you can be sure that nobody was filing away vast chunks of precious metal - it's all precious when you hammer sheet from ingots by hand - because they were too lazy to learn the technique of shrinking, or "gathering" as it is usually called. Filing is the only way to metal finish an unpainted object with hard edged damage, and teeth marks are not acceptable. With no such marks, planishing with a polished hammer and dolly will give any level of smoothness you like, while removing NO metal. While shrinking can be done with a steel hammer on a steel dolly, it's easier and quicker to have one or the other be wood, preferably end-grain hardwood. The end grain grabs the metal just like the teeth on the useless tool, with no damage. The trick is to hammer bumps down in such a way that a portion of the movement is in the (local) plane of the sheet, which compresses and thickens it, reducing the area. If the ding we speak of is in the leading edge, as seems the case, then it is likely that not only is no shrinking required, but some may have already occurred in the formation of the ding, If the ding is the result of a pointy thing hitting it, then there may be some stretching, but that can be removed and more "shrink" can easily be introduced in the preliminary straightening. That leaves it a bit shrunk for final finishing, which is the ideal case. A key rule is that when using a steel dolly and hammer, a "thunk" is shrinking metal, and a "tink" means the hammer has hit the dolly with the metal squashed between, which means stretching. FRM |
| FR Millmore |
| I was able to successfully shrink my coupe doors using the conventional method with an oxy-acetylene torch. I found that aluminium shrinks much more readily than steel. The process, however, can be rather tricky because aluminium does not change colour when heated and if you overdo it the "blob" will fall down and leave a hole! DISASTER! If you are not fairly confident I would strongly recommend getting someone who is experienced to do it. I think that cutting holes and/or hammering (even with a so-called shrinking hammer) would be fatal! In brief, the technique is to intensively heat an area about 20 cm across and you will find it rise like a large pimple (quite different to steel) and then QUICKLY but carefully firmly tap it down (ie around the edges of the raised area and also on the pimple itself) using a flat-faced wooden mallet with a dolly held loosely behind the panel so as to control how much you are depressing it. Then quench with a very wet rag and you will be surprised how much it will shrink with only a few repititions! If the door is too "full" (which it is almost certain to be if damaged/dented) it must be shrunk but it would be better to get an "expert" to do it rather than ruin the panel! |
| Barry Bahnisch |
| Lots of good suggestions. One issue I didn't see is that aluminum work hardens quickly. You need to anneal it before you start work and, if you need a lot of shape change, several times during the hammering. Otherwise you will get stress cracks- either now or after a few years on the road. The best annealing process I've seen is to take a "feathery" acetylene flame and carbon the surface. Then increase the oxygen to just short of normal- slightly soft or reducing. Heat the aluminum just enough to burn off the carbon. You shouldn't use a neutral or oxidizing flame since aluminum oxidizes quickly. Shrinking can be done with a soft hammer agains a hard dolly. A maple mallet is the traditional tool although most people use plastic now. Set the pannel on the apropriate -shaped dolly and whack it softly- just enough to move metal. It will conform a bit then stop moving. Don't swing harder- it has work hardened and you need to anneal again. I've done this a couple of times on smaller or more contoured surfaces- my A's bonnet nose for one. It would take me a couple of days to do an MGA door not including finding/making the correct dolly. Regular heat shrinking is really tough because aluminum conducts heat quickly. You can't wack the metal while the bubble is still hot. You also get rings of hardened sheet surrounding the soft "bubbles" and high residual stress. This can cause waves to appear over time as road vibration stress relieves the panel. How much is a door skin? If coupe skins are expensive, can you use a roadster skin and lap-join it below the door handle? Big flat areas are easier to keep straight than make straight. Hope this helps, Bill |
| Bill Eastman |
| I have wondered for a while whether there might be enough metal in a roadster door skin to reshape the top for a coupe door skin. I just did some measuring and I think it would work. The ear on the roadster skin that mates with the cowl would be mostly cut away. A small bit would have to be flattened and turned up along with the remainder of the top to form the window flange, but it looks to me that there is enough material for this. |
| John DeWolf |
| John- over 20 years ago I was able to get new skins for my coupe in England,since then the company was bought by Moss Europe.I have a catalog from last year,I'll look for it and see what they have. Gary |
| gary starr |
| Thank you for all your comments. I'm obviously way out of my comfort level on this work. I think the solution will be to find a second hand door or buy a new door skin which are available from Brown and Gammons in England, Unfortuneately the cost of the shipping was about the same as the door which put it around $700, delivered to my door. Alternately I could live with the door as is and see how it looks with some filler. Thanks to everyone for lots of comments and ideas, Andy |
| Andy Preston |
| Andy: Is it the driver or passenger side door that you have a problem with? I have a spare driver-side coupe door that I would consider parting with. Regards, M.D. '57 Coupe |
| M. D. |
| andy,yes you can shrink it your self.slow and steady,low temp(450)and wet towels.easily done,i think after 50+years all mga doors had a knee in them one time or another.cc |
| c.callaway |
| Andy- check this out they only have right hand drive ones listed now,the only difference I believe is the key lock is in the right side door. 92.95 pounds http://www.moss-europe.co.uk/MossUK/ProductList.aspx?SubSubCategoryID=MGA_MGAS021B1#top It's hard to find a door any better than what you have. Let us know what side you need. Gary |
| gary starr |
| Two door skins for sale on Ebay right now. |
| Gordon Harrison |
This thread was discussed between 09/09/2006 and 12/09/2006
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