Metal Shaping

The following is a summary of notes taken during a Reynolds-Alberta Museum, Metal Finish and Repair on Automobile Bodies course, taught by Darren Wilberg (Head, Restoration Services) on February 25, 2001.

Metal Surface Finishing and Repair - Part I

Metal Body Finishing

A high quality permanent repair to metal body damage is a must for a top restoration. The following technique will result in an high quality permanent body repair that will not discolor paint, crack and will require a minimum amount or preparation for surfacing coating.

Tools in order of typical use:

Wooden mallet: Also called a Tinners Hammer. Used for beating metal without causing metal stretching. Best material for heads is boxwood or maple. A typical hammer has a 3 inch diameter head and a 14" long handle.

Slapping file: Not commonly used anymore, can be made from straight files (10 inch flat file with an s-bend). Used to finish after the wooden mallet, is used to hit metal surface with glancing blows. Application results in some metal shrinking and stretching to repair surface. Can be purchased from Eastwood.

Body hammers: Come in various shapes and sizes. Used to finish body repairs with dollies. Used for finishing off small defects.

Dollies: Come in many shapes and sizes, used to provide opposite force when using wooded mallet, slapping file and body hammers. Avoid on Dolly hammering except for final finish with glancing blows. Common type is the universal Dolly.

Vixon Body files: Course file used for showing surface contours and final truing of surface.

The goal of metal repair is to retain/preserve the original factory work hardening in the metal and remove the rest. The cold working of metal stress hardens the metal and makes it more brittle and harder to work with. The goal of metal working is to remove stress rather than adding it by further stretching and shrinking the metal. All major deformation work should to be done with a wooden mallet. You can almost repair anything with patient and practice. Don't be scare to try, time is on your side.

First rub the surface with welders caulk or other suitable material to see the what the surface profile is like, when the dent starts to get smooth a body file will need to be used to check the surface profile. Start removing dents from the outside in. You need to get the edge shapes close before moving to the centre damage. For example with fenders you need to work in the perimeter to get the basic shape back. For removing the large dents (deformations) place the best fitting Dolly in behind the dent (on the low spot) and hammer on the outer surface edges where the metal is raised with the wooden hammer. Start with a Dolly that best fits the dents profile. When removing a dent also start on the outside, work your way around the outside and then work your way in to the centre. Often you need to examine and determine how the dent occurred and work backwards to reverse the deformation.

After the main deformation is removed with a universal dolly (rounder dolly) and mallet, use a flatter dolly and a slapping file to remove the remaining smaller deformation. The slapping file is used to stretch the remaining body deformations into place. To check your progress use a body file to check your profile (and of course your hand). Remember a body file is to be used at 45 degree angles, no straight filing. Finally use the light planishing (body) hammer to smooth the last deformations. Only with the slapping file and body hammer will there be any on-dolly hammering to clean up the deformation. Minimize on-dolly hammering and when done it should be done with a glancing blow and not a direct hit. On dolly hammering will stretch the metal and cause it to deform more. Remember use a wooded mallet for all major work.

Rule of thumb, you should never use a grinder as it will cause work hardening to the parent metal and often cause more damage than caused by the original dent. After a good job of body hammering all that should be needed before coating and priming is a light sand with an orbital sander.

Special Notes:

Most cars are made from 20 GA sheet metal. For replacement use a cold rolled mild steel sheet metal.

When restoring a vehicle always replace the metal wire around the edge of the fenders. It is normally where this wire has broken that the fenders crack, and if it is not repaired it will crack again in the same spot. To replace the wire, bend up the metal edge with a screw driver or chisel, pull out the old wire and replace with the same diameter wire, bend the metal edge back into place with a body hammer and dolly.

For high stress areas, annealing the metal by heating it and allowing it to cool slowly will soften the metal and allow it to handle higher stresses and be less susceptible to cracking.

The following is a summary of notes taken during a Reynolds-Alberta Museum Metal Finish and Repair on Automobile Bodies course, taught by Darren Wilberg (Head, Restoration Services) on February 25, 2001.

Metal Surface Finishing and Repair - Part II

Lead Filling (Grandpa's Bondo)

Leading is an old technique that works well as the lead actually chemically bonds to the car surface rather than plastic body filler that only sticks to a rough surface. Lead will not crack and is flexible, so it is good for areas of high vibration (places where plastic body filler will crack). However, the flux from tinning needs to be cleaned off with ammonia as the acid can affect the paint and any surface coating over time.

Tools in order of typical use:

Torch: Propane or acetylene will work. With acetylene use a soft flame tip (no oxygen required)

Solder paste: 70% tin / 30% lead, Cram-co is a popular brand

Lead (body solder): One lb bars available from Acklands

Solder Paddle: Wooden paddle made of maple, shaped like a trowel used to spread the molten lead. The paddle is soaked in tallow and a coat of beeswax is applied to the base to stop the lead from sticking.

Lead alone will not adhere to steel, so the surface needs to be coated with tin first. The tin coat is applied using soldering paste. The paste is usually 70% tin and 30% lead. To tin the area use a soft flame (propane or acetylene torch) to warm the area. To avoid warping keep a large area of the panel warm. You will find that the tinning melts very easily. After the surface is hot enough apply the tinning with a brush and then wipe down the tinned area with a cloth to remove any excess. After the area is wiped down you do not want to see any black spots, this indicate corrosion spots and these need to be cleaned out. It may be unavoidable to have some black spots in crevices. Normal plumbing solder can be used to check if the temperature is ok and to check if the lead will stick. The metal and lead will need to be separately heated to 375 C for the leading to work. Push the lead into the metal joint, the lead upon contacting the hot metal should have the consistency of butter, if it gets even a little too hot it will turn to a liquid and run down. You will need about a 1 lb of lead per 6 inches of a typical roof joint. Make sure the initial tinning is down well as the lead will not stick to steel and as the tinning needs a higher temperature than is required to melt lead, the lead will all run off if you have to even add a little more tinning. Be careful not to file through the lead because as the tin is thin it will also be damaged and then you have to start again if you need to add more lead in that area.

After the lead is on use a soldering paddle (maple wood paddle boiler in tallow (fat) and then dipped in beeswax as a lubricant) to smooth the lead, carefully heat the lead and work it into shape with the paddle. You will need to take your time and when you are finished just let it air cool. Once the joint is cool (doesn't take long) just file is smooth, use old files as the lead will plug them. Chalking the file before hand will held keep the file clean.

Special Notes:

Remember to always file from the hard steel surface on the lead and not the other way around

Dont rub your hand on the shiny lead as it will get into your skin, use a cloth under your hand to feel if it is smooth.

Don't use a grinder as lead dust isn't good for you.

Basically finish the same as body filler

Shrinking metal is more difficult. Shrinking metal is the process of making metal thicker (the opposite of hitting it with a hammer). A shrinking tool is available but it is not recommended for use with mild steel sheet metal as it is very, very slow. A simple way to shrink metal is to use a claw hammer to kink the edges then hammer them out with the wooden mallet. This method will slowly produce the outside curve of a fender and is a similar technique to that used in furnace ducts. The claw hammer method works real good on aluminum.

A faster method used for fenders and where lots of shrinking is needed uses the acetylene torch to heat shrink the metal. Using a neutral flame (no feather) heat triangular sections to red hot and push metal together with pliers, the more the curve needed the closer the heated triangular areas should be. The larger the bend or web of the curve the larger the amount of material that will need to be shrunk. Usually use a maximum web of 1 to 1.5 in. Generally it is easier to butt weld pieces together than to make a large web.

The two methods can be combined to shrink metal i.e. bend with a claw hammer and then heat and bend with a wooden mallet. With lots of patience a whole new fender can be made from scratch. The heating method can also be used to remove bulges from metal plate (i.e. hail dents).

Special Notes:

You will need to curve the metal more than needed, because as you pound the metal smooth again the curve will diminish.

To make a large curved object, it is generally easier to make lots of small pieces and butt weld them together.

Butt Welding

The body man at the Reynolds-Alberta Museum uses an acetylene torch for 99% of his welding, a little TIG and MIG welding is only used for those hard to get at places. Most of the welding done it to replace damaged metal due to corrosion or to repair bad past repairs. Acetylene welding has the added benefit that it heats the metal and anneals by cooling slowly compared to methods that use a shield gas that also causes faster cooling. Anneal metal is easier to work with, but you do have to watch that you dont over heat and warp the metal.

Common Welding techniques:

TIG: Compared to acetylene welding TIG welding has a smaller HAZ (heat affected zone) because it uses a cooling shield gas that quenches the weld a TIG weld is less ductile and thus harder to deform than a gas weld. TIG is real good for light work.

Brazing: Brazing with bronze has an advantage as it can be done at much lower temperatures which allows easier heat control. Brazing can only be done for lap welds as brass butt welds have very little strength. Brass on steel will also accelerates corrosion due to dissimilar metals and plastic filler will not stick to it.

MIG: MIG is easier to weld and can have a cooling flux which quenches the weld. MIG welding must use a filler metal so metal build-up with grinding can not be avoided. It is difficult to butt weld and generally can not be ground flat on both sides.

The most important part thing to ensure a good acetylene gas butt weld is good metal edge preparation. The two pieces of metal must fit so there is less than 1/16" of a gap. When making replacement pieces that are pre shaped, make the replacement piece 30% bigger and keep as much of the original piece as possible. The metal can be cut with tin snips or with an arbor saw. Remember the most important part is alignment, only a little gap can be allowed as this method relies on the surface tension of the molten steel to hold the liquid steel in place.

It is absolutely essential that the torch must be balanced. Use a No. 1 tip with less than 3 lbs acetylene. To balance your torch, with the oxygen off, place the acetylene hand control at 75% then adjust the regulator so the flame has no soot but is not lifted off the tip. Increase the regulator until the flame lifts off the tip and then back-off until the flame comes back to the tip. Now balance the O2. Turn the oxygen regulator at the bottle off and open the oxygen hand control 75%, now adjust the oxygen by opening the regulator until a neutral flame is achieved. To much oxygen will result in a dark blue flame and will cause the weld to oxidize. You want a bright blue flame with no feather. To achieve a good weld a good set of regulators will be needed. If you use your torch for a lot of cutting you may find you will have trouble controlling at the low pressures.

Place pieces of metal close together and tack spot weld by melting the steel, you should not need to use any welding rod (use some parent metal if you need some where you burn a hole through). Start at one end and only do about 3 tack welds about 1 inch apart. The tack welds preheat the metal as you go. After tack welds if you need to smooth out use the hammer and dolly, hammer only when you need to smooth out your weld. You may need to let the metal cool after every couple of tacks as the heating metal will pull apart, when it cools it will come back together so you can continue. Just worry about the end your are welding at and do not tack both ends, start at one end and work towards the other. Again only work about 3 tack ahead. After the tack welds carefully heat the two metal edges you wish to weld together, heat them until the steel metals. Use a slight wrist wiggle as you weld the two seams together. Weld about one inch at a time. Never weld out to the last edge, stop about a ½ inch from the last edge. Let the metal cool until the last edge comes together and then tack the last edge and weld back to the rest of the weld. When working to an edge watch for burning holes. Finish of the weld with a hammer and dolly and file the sand prime and paint. Makes a good workable weld.

Special Notes:

Remember this techniques relies on surface tension for holding the molten steel in place so panels need to fit really snug.

Avoid finish grinding, with this technique you should only need to sand and buff.

This is not hammer welding, you should need to hammer very little.

There will always be a little weld track.

Note no filler should be needed.

This method will leave the metal easy to work with.