In the last installment of this series we went through the process of shaping a patch panel, welding it into place, and doing the initial straightening. This time we’ll cover the process of metalfinishing: getting the ultimate smoothness on the panel, using only hand tools.
You might ask, is metalfinishing required when working with patch panels? In many cases, it’s not. Most patch panels require the use of at least a little filler material, and there is nothing wrong with using filler as long as it’s not built up too thickly, and not used to build up edges. In some situations—with smaller patches in particular—you may find it’s better to work the metal to perfection. This can take less time than it does to carefully clean the metal, mix up some plastic filler, spread it on, clean your application tools, and then wait for the filler to harden, sand it smooth, and then repeat the process at least once again, since it’s rare that you will get it perfect the first time.
There are some situations where metalfinishing is mandatory, like when working on a part that will be polished or chrome plated. No filler can be used in these situations, and I think it’s good to learn the metalfinishing process so you’ll be prepared when it may be required.
Once you’ve developed some skill using hammers and dollies you can get metal panels reasonably smooth, but it’s hard to get them absolutely perfect with these tools alone. Metalfinishing involves using a file. The file must be used with care, since it’s important not to thin the precious metal thickness any more than absolutely necessary, but filing is a superb way to reveal any low spots, which can then be raised by using a couple of techniques that we’ll cover in depth.
The first step is selecting the proper file. Metalfinishing is done with a Vixen file, which has curved teeth with a very coarse pitch—usually 10 to 12 teeth per inch. While it looks like this sort of file would be too aggressive for doing sensitive bodywork, it turns out that the broad, continuous tooth profile shaves off just a tiny amount of metal, leaving a very smooth surface.
These files used to be available in many shapes, but these days there are only two styles available: flat and half-round. The half-round files are curved something like a stick of celery—straight from front to back but curved from side to side. The curved files are useful for getting into concave areas, but for all convex panels, flat files are best.
You can get both wooden and metal handles for the files. Some metal handles allow you to adjust the shape of the file, making it slightly concave or convex along the length. This can be helpful in certain situations, but for most of the work I do I prefer the wooden handle. It keeps the file laser-straight, weighs less than metal, and feels more comfortable in my hands.
The first step in metalfinishing is to run the file lightly over the surface of the metal. The file will only touch the highest areas, so anything that the file does not touch is “below grade.” Next, the low spots are gently worked up; this can be done by hammering lightly on-dolly. I usually use a slap hammer for this because it’s more gentle than a hammer and it covers a broader area.
After the first round of filing and hammering the surface is filed a second time, usually revealing fewer and smaller low spots. For the final smoothing, I use a Bull’s-eye Pick. This tool has two arms hinged together—the top arm has a “gunsight,” which is centered over a low spot and when you squeeze the handle the other arm strikes the metal right in the center of the gunsight. This makes it very easy to raise tiny low spots with precision. You have a lot of control over how much you move the metal, governed by how rapidly you squeeze the handle. Usually three of four rounds of “picking and filing” are sufficient, and at this point the file should touch every spot on the surface of the metal, which indicates all the low spots have been removed.
I like to sand the file marks out of the metal, so the next step is going over the surface with an 80-grit sanding disc, followed by 120-grit. This gives the metal a very bright finish, highlighting the smoothness of the metalwork. If you are working on something that will be polished or chrome plated, it doesn’t take a lot of work to go from a 120-grit finish to a full polish.
Tune in next month for the final article in this series: the wonderful world of hammerforming!
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