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This is an inexpensive thickness gauge for sheetmetal.
Q. I need to make some patch panels for my project truck. Can I use metal cut from old cars and trucks to make my patch panels? I don’t want to have any problems down the line with mixing old metal with new, and I’ve been told that newer cars are made from some special steel.
Via the Internet
A. There is a lot of variation in the metals used for the bodies of cars and trucks. Certainly, you often can use metal salvaged from old cars and trucks, with a few caveats.
First, any metal that you are welding into your project vehicles should be exactly the same thickness as the original, if at all possible. Some early classic trucks used 18-gauge steel (about 45 thousandths of an inch thick) for the bodies, and not many passenger cars were made of metal that thick. The general trend has been to use thinner metal on newer cars and trucks. Some of the cars made in the last 10 years have body panels as thin as 23-gauge steel (about 23 thousandths of an inch thick), and metal this thin has no place on classic trucks.
To further complicate matters, many newer cars and trucks use High Strength Low Alloy (HSLA) Steel, or sometimes Boron Steel, which are quite difficult to work with, and may have special requirements for welding. I don’t recommend using this material for patch panels.
If you stick with donor vehicles from the ’80s or earlier, you should be in good shape, as long as the thickness matches the metal your truck was made from originally. You can buy inexpensive gauges for measuring metal thickness, which takes all of the guesswork out of the equation. It’s pretty hard to judge the difference between 18- and 19-gauge metal by eyeballing it, since they’re only about 5 thousandths of an inch different. Even this small difference in thickness really changes the workability of the metal, and that’s why I don’t recommend mixing different thickness materials.
On the other hand, new steel is not usually very expensive, even when purchased from a small, local supplier, and when you factor in the labor it takes to cut out, and then clean panels taken from old cars and trucks, you may be better off buying new metal, or to buy aftermarket patch panels if they are available.
Q. I’m splicing in a lower outer doorskin patch panel on my ’57 Chevy pickup. I removed the inner door panel first, then clamped the new and old panels together using Clecos, and cut both at the same time so the fit was perfect. I used a couple of braces cut to the profile of the doorskin to hold the panel in position and tack welded it in place. At this point everything good and properly aligned, so I proceeded to finish weld the panel short sections at a time and used compressed air to help cool the panel down after each round of welds. I got it welded together with minimal distortion, but there is a noticeable bend between the old and new panel when looking at it in profile. At this point I have full access to both the front and back of the panel; what is the best way to work it back into the correct profile?
Via the Internet
A.I presume that when you view the panel from the outside, the weld has “sunken” somewhat, creating a slight valley. This is the most common type of distortion that people get when welding patch panels into place.
I think the easiest way to deal with this is to first sand the weld bead flush on the outside, and then you can hammer from the inside against a flat dolly. This will move the metal in the right direction, and every time you hit “on dolly” it will stretch the welded area, reversing the shrinking that typically happens with any welding. Be very careful not to hammer any more than necessary, or you can get yourself into more trouble!
If the weld has pressed out (which does happen occasionally), I’d still sand the outside of the weld flat, but hammer on the outside of the door, backing the metal with a slightly curved dolly. CT