The use of the oxyacetylene torch is necessary in the true heat shrinking process. This process comes into play when you need to straighten an expensive-to-replace or difficult-to-procure part. If you didn’t have a torch like this and thus had to replace this part (possibly a quarter panel), it might lead to the total of an otherwise fine vehicle and the loss of a job for you, perhaps when you most need it.
The damage may be fairly localized but deep, causing the metal to be stretched. If the panel is mild steel body metal and not high-strength low alloy (HSLA), heat shrinking after straightening is an option for you.
The Heat Shrink Procedure:
1. Remove the damage to reveal high spots and stretched areas.
2. Attach a small welding tip and set gauges for 5 to 7 lbs. for gas (acetylene) and 12 to 15 lbs. for air (oxygen).
3. Crack the gas knob and ignite the torch, dial in air to neutral flame J.O.F. (just off feather).
4. Identify the highest spot. Place a series of quarter- to dime-sized cherry red hot spots around that high spot, driving the high-stretched metal into the hot spots one at a time.
A flat dolly is placed on the backside of the hot spot immediately after heating and a hammer is applied around the hot spot, driving the molecules into the more fluid hot spot to thicken it. Compressed air is immediately applied. Then, move to the next spot until you’ve returned the contour to its proper shape…a very viable process.
What? Do you really need to know this? It all depends on your goals as a technician. Can you be an expert collision repairer without being a gas welder? I think so. But if you want to be at the top of your field, you should be able to gas weld. It opens the door to TIG welding, silver and bronze brazing and hammer welding.
These are all skills that a highly skilled auto body/collision repairer/metal man should aspire to, and to a great extent, are achieved through practice and self-education. Don’t despair…if you’re interested, you’ll learn. I’ve used all of these skills and continue to use them.
Should you consider oxyacetylene welding?
1. You can weld torn or cracked mild steel with a gas welder and produce a better stress-relieved weld than a MIG weld without disabling airbags, electronics and radio codes.
2. Consider this: a tear in a piece of steel can be welded, with access to both sides, and finished so that you can’t tell where it was welded before painting. This was a process used by Porsche on the nose panel of the 356, a body style they carried for 17 years. Hammer welding or forging of your welds allows you to finish a weld to invisibility (see Photos 1-3).
3. TIG (Tungsten Inert Gas) welding produces some of the finest welding possible. The basic skills for TIG welding come from oxyacetylene welding. They’re exactly the same skills, with the addition of a foot control, to increase or decrease heat required. The physical coordination required (holding a gas torch in one hand and feeding filler rod into the weld pool) is exactly the same for TIG welding. Cut some strips of zinc-free 22-gauge metal and practice with your oxy torch. Weld with a small tip and the 5- to 7-lb. gas and 12- to 15-lb. air setting. Use a J.O.F. neutral flame. You won’t become proficient in an hour, so be prepared to spend some time doing it.
4. I mentioned hammer welding, which is the common description for forging a weld. By heating a 1/2-inch of a gas-welded joint to cherry red and placing the crown side of the dolly on the backside, then quickly hammering the weld site in the “hammer on dolly” method, you can forge the filler rod into the pieces being welded, which allows metal finishing without filler. This method allows a stress-free weld because of the temperature you’re working at.
Allow the weld to cool naturally. This will also take some practice.
Here’s a hammer welding success story: A customer (a good one, I might add) collected fine automobiles, but liked to drive them on extended tours. He ran a red light in Winnipeg with his 1936 Packard Dual Cowl Phaeton, and the Dodge that hit him tore off his front bumper, damaged the radiator grille shell and thermostatically controlled shutters, and ripped the fender. The adjuster and I agreed on 40 hours of repair on the fender. It was repaired using the hammer welding process and no filler. All the damaged parts were repaired and re-plated, and my customer was happy again.
5. Wondering where you could use the silver/bronze brazing process? It used to be quite a common practice to braze parts onto an automobile with the oxyacetylene torch, but those days went away with the advent of high-strength steels. But brazing is coming back in the MIG form because it can join metal together at a much lower temperature than steel welding. You can do oxyacetylene brazing on cast iron successfully.
Case in point: I silver brazed a continuous, solid, German Silver molding together, completing the entire circuit around the fenders, running boards and front and rear aprons of a 1928 Mercedes Benz SSK. One solid complete molding!
Soldering and Leading
Flame soldering with oxyacetylene is ideal for the times when you need to solder something that requires more heat than the average soldering gun can produce. Perhaps you’re making or repairing a starter cable and need to attach a new stake connector at the end of it. Soldering with acid-free rosin core solder, using a mild soft flame, is the most positive connection you can make bar none.
Leading has been called a lost art. Well, it’s not an art and it hasn’t been lost (see Photos 4-6).
It still has its uses, where a thick fill is needed (over 1/4 inch) on an edge or mating flange.
Take this example: A Land Rover Discovery was hit in the door pillar, which was part of the firewall/cowl. The dealer body shop manager told the adjuster “there’s nobody that can repair that pillar.” The adjuster told me, “I thought of you when he said that.”
The Land Rover wasn’t scheduled to make this part until an unknown time and we were no. 3 on the waiting list.
The car had been sitting for more than a year when the insurer gathered up the parts (making a couple of trips) and brought it to me. I removed the damaged part from the rest of the firewall/cowl where it was spot welded, straightened it to close tolerance and welded it back on. I fit the new door and leaded the exposed door pillar and hinge mounting area. Beautiful…the SUV was back to its owner in a month, and I had fun and was paid well for having it.
I know, I’m reaching here. But I feel this is something you should know if you’ve read this far.
Every master collision repair man has tools in his box that he made himself. That’s one of the things that make him a master.
The set of pry bar picks in Photo 7 was made from the torsion bar springs that are commonly used in most deck lids. You can either reclaim a couple rods out of a total, or go to a wrecking yard and remove them. And make sure to use a set from a heavy deck, like a frame car (Caddy or similar).
1. Choose torsion bars that are at least 3/8 inch in diameter or close.
2. These are spring steel, so heating to the shape you desire will be necessary.
3. Cut ends of the bars off and cut to desired length using abrasive saw.
4. Determine shape you want for handle end and pick end.
5. Get a bucket of water deep enough to immerse the ends of the rods.
6. Place rod in a vice, heat to cherry red and bend to desired shape. Quench in water.
7. Remove discoloration from heat affect zone. Wire wheel, Scotch Brite or sand paper will work. Metal should be bright in this area.
8. Re-ignite your torch to a neutral flame and heat the heat affect zone you previously heated to a dark blue color.
Do this slowly and evenly, so that you get a uniform blue over your entire heat affect zone. Immediately quench in water.
9. Remove blue color from heat affect zone using same method as before.
10. Replace tool (it’s not a rod anymore) in vice. Re-ignite torch and, using fast, even strokes, play the flame over the heat affect zone until the bright metal turns a straw color. This won’t take long, so focus. Allow to air cool. You just made yourself a set of valuable pry bars. Mine have lasted more than 40 years. I also made a set for my vo-tech instructor, painted them and put his initials on the shafts. It looked like he got a little choked up when I presented them to the old guy.
Dead or Alive?
Is the oxyacetylene torch dead? Well, you’ll have to be the judge. To master metal workers, they’d rather give up a toe or maybe a troublesome family member than this useful and valuable instrument.