Replacing Wood With Metal
QI would like to thank you for a great column and sharing your vast knowledge. I am a retired automotive engineer with many years of hands-on experience, and I love building hot rods. I am always eager to learn something new and your writing and DVDs have helped to improve my sheetmetal working skills.
I am building a “Dare to Be Different” ’34 LaFayette four-door sedan, built by Nash. The body is a “Seaman composite hardwood and steel body” in which most of the wood needs to be replaced. What gauge steel tubing would you recommend to replace the wood in the body? In the doors some of the wood is 3/4x1 inch, and there is no room for anything larger. Some odd sizes and shapes may require fabrication from sheet stock. Would you use the same gauge metal for that?
The second question I have deals with the rain gutter, which I would like to retain. The original construction has a wood support under the lower edge of the roof. The lower edge of the roof sheetmetal has a row of small slots punched through it. The gutter, which is formed steel, has a row of nails protruding from the back side. The gutter effectively “nails” the three pieces together. When assembled originally there was some type of seam sealer between the gutter and the roof.
Since there will be no wood to nail the gutter to, I am trying to figure out a good way to reattach it. I have thought about putting sealer behind the gutter and MIG welding the nails to the top from the inside. I am concerned about the sealer burning during the welding, allowing rust to start there later. My second thought would be to solder the gutter to the roof after the bracing is welded inside. I am considering using a higher strength solder like a 70-30. I would appreciate any suggestions you might have for attaching the gutter to the edge of the roof. JackPatterson ViatheInternet
A In many cases, 1/16-inch thickness tubing should be fine for replacing wooden structures. If you have to build hollow shapes from sheet stock this would be the minimum thickness, although 14-gauge might be used in areas where more strength would be beneficial. There are a few areas where I would go thicker, such as the doorjamb areas, where the door hinges and the latch striker plates go. You want these to be very beefy, so I’d step up to a full 1/8-inch wall thickness in these areas, and anywhere else where you want ultimate strength.
Re-attaching your rain gutter is a pretty challenging problem. I think your idea of soldering the driprail into place is probably the best plan.
When doing soldering of this nature, you tin each part separately, then align the parts, heat them gently, and flow some more solder into the joint. If the body is in its normal orientation, gravity makes it difficult to hold the gutter tightly against the body. It might be better to rotate the body on its side, so gravity will help hold the gutter against the body. There are rotisseries that are great for rotating bodies, or in a pinch you could probably roll the body gently over on its side, using an old mattress to cushion it.
Solder is designated with the tin content first and the lead content second, so the 30-70 solder commonly used on autobodies is 30 percent tin and 70 percent lead. This lead-rich solder is designed to stay in a plastic state over a broad temperature range, to make it easy to paddle into shape, and it is not as strong as 50-50 solder. I’m confident that 50-50 will be fine for your application. For example, millions of radiators and gas tanks have been held together with nothing more than 50-50 solder.
Steel tubing comes in a wide range of sizes and shapes, but for some odd-sized inner body structures you may have to make your own by welding together strips of sheet steel.