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Q: I just bought two of your DVDs recently, TIG Welding Basics and Chopping and Sectioning. In the second DVD, the Studebaker truck is all clean metal. This seems to be standard operating procedure for any metalworker doing serious metalwork on a car. My question is, how do you suggest getting an older vehicle to this state? How do you keep the bare metal shiny and nice while the metalwork (chopping, channeling, and panel replacement) progresses?
Via the Internet
A: There are many ways to clean old metal. Plastic media-blasting and soda- blasting are two of my favorite methods, and they do a great job stripping off old paint and any plastic filler, leaving the metal clean and shiny. These processes don't remove rust, however, so any rusted areas will have to be treated some other way. There are chemical stripping processes that clean both paint and rust from metal completely. When properly done, the stripped parts are neutralized after dipping and baked to ensure that all the stripping solution is completely eliminated.
Sandblasting can be used to remove paint, filler, and rust, but the blaster must use extreme care to prevent warping the panels by using too much pressure. This process leaves a rough surface and broken sand particles embedded in the metal surface, which can dull your files if you plan to metal-finish the panels. A light sanding with 80-grit sandpaper will usually remove any remaining blasting grit from the surface of the metal, saving your expensive files, and the parts need to be sanded before painting, too, since paint won't stick properly to a surface with crud embedded in it.
On the Studebaker truck project, Joe McGlynn used the chemical dip process for the smaller panels (doors, hood, fenders), and sandblasted the cab since the local stripper's tank wasn't big enough for parts that large (some strippers have tanks large enough for an entire car body).
Humidity is the most common culprit that causes metal to rust. Joe's shop is in Scotts Valley, California, about 10 miles from the ocean, and bare metal in his shop stays rust-free for years without any special protection. My shop used to be in Scotts Valley, but I moved to Freedom a few years ago, which is only two miles from the ocean, and I'm amazed at what a difference there is between the two locations. After about nine months, most bare steel left uncovered in my new shop starts to get a light coating of rust!
Another factor that can cause rust is the salt and acids on some people's hands. It's interesting how much people differ in this respect-when I handle metal, it normally doesn't cause any rusting, but if I am perspiring, it does! Some people have body chemistry such that wherever they lay their hands on metal, the next day you will see rust spots.
There are many ways to prevent surface rusting. Shooting the parts with primer is probably the best way, and if the parts will eventually be painted, they'll have to be primed at some point anyway. Covering the metal with oil or grease is another pretty foolproof way to protect the metal, but it makes the parts unpleasant to handle, and you'll have to clean the stuff off when you work on the panels. Be scrupulous about cleaning all traces of oil or grease off the parts before painting. Some people use a spray-on coating such as WD-40, which isn't quite as effective but is easier to apply. There are also some products that contain phosphoric acid, such as naval jelly, designed for stripping light rust, that leave a phosphate coating on the metal that retards further rusting to some degree.
Both media-blasting and dipping have advantages and disadvantages. Dipping the parts is safe in terms of not causing any warping of the panels. If the parts are properly treated after dipping, you should have no problem, but when parts are dipped, if the solution that wicks into tight seams between overlapped panels isn't completely neutralized, over time it can ooze out of the seam and cause rusting at the edges of the joint. This is a particularly unhappy event if the parts have an expensive paint job on them when the rusting starts. The dipping process is considerably more costly than media-blasting, too.
Media-blasting, or sand-blasting, can cause warping of the panels, especially if the work is done by someone who is careless or inexperienced. A good sandblaster will know how to manage the process so that no damage is done, but I can't tell you how many "Dear Professor Hammer" letters I've received from people whose panels were damaged (or ruined) by well-meaning but heavy-handed blasters. Plastic media-blasting is pretty safe in terms of not causing warping, but it doesn't remove any rust. Perhaps a good blend of techniques would be to plastic media-blast the majority of each panel and then sand-blast any rusty areas.
Regarding the patch panels; the big consideration here is to not let any part of the cab get out of alignment at any time. The larger the area you have to cut out, the more risk there is of losing the alignment. Sometimes, for major work, the cab should be braced with tubing before large areas are cut out. For repairing smaller damage, like a cab corner, this may not be necessary. Once a panel is cut out, tack welding the patch panel into place will restore the strength pretty well in terms of alignment, but there is always some chance of warping with the finish welding. For this reason, I prefer to cut out each area, fit a patch, tack, straighten, and finish-weld it before I move on to the next area.