My Old Landy
Engineering Mayhem
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They look superb, I would be happy with that result!(I thought I'd post this little mini-project in this thread instead of my M37 restoration thread, since the technique has other applications.)
The ID data plate for my 1954 M37 was missing, and I could not find a proper reproduction plate, so I thought I'd try my hand at making an etched-aluminium facsimile that was as near as possible to the original plate.
To start, I found a photo of an original data plate that would be correct for my truck and squared it up with Photoshop so that it could serve as a model: The plate is 4" wide and 2" high.
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Then I made a facsimile of the plate from scratch in Adobe InDesign. That took a while, as I had to modify some characters to come up with a pretty close match to the original fonts.
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Next, I printed a mirror image of the design on special inkjet transparency film. The film has a slightly frosted coating on one side, which apparently allows it to accept more ink than an ordinary transparency film. I maxed out the CMYK channels for the black areas in InDesign and set the ink density higher in the printer control app in order to achieve pretty decent opacity.
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I then adhered a sheet of photoresist film to a carefully cleaned aluminium sheet, working under subdued incandescent light (the film is UV sensitive). It's hard to get this stuff on without trapping bubbles. There is a way of doing it with water, but I tried it and didn't like that method, so I just had to refine my pressing and rolling technique on some practice pieces until I managed to adhere a few sheets without bubbles. Here's one of them:
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I placed the printed film image emulsion side down on the photoresist film, placed a sheet of plain window glass over it, with a piece of foam rubber behind it to keep it pressed tightly against the glass, and exposed it to direct noon sunlight for about 30 seconds. After exposure I removed the thin plastic protective layer from the photoresist film and 'developed' the photoresist in a mild solution of washing soda, which removed the unexposed (unhardened) portions of the photoresist. I then etched the aluminium with an acid solution (I'm still working on figuring out the optimum formulation, so I won't list it here yet). I had a few trial and error (mostly error) runs before I got a couple of decent results. Here's one of them:
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Next, I chemically darkened the etched area with Aluminum Black from Birchwood Casey.
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Soaking the plate in acetone for a few minutes loosened the photoresist and allowed it to be brushed off easily with a soft brush. I then trimmed the edges to the cut lines with my latest tool, a 12-inch shear.
Here's the end result so far. The etching leaves the letters slightly raised, like the original data plates. I'll punch the rivet holes later with my Roper-Whitney punch set instead of drilling them. I'll use a 3/32" number and letter punch set to add the serial number and other data. I'll probably make a couple of extra plates in case I mess things up when I'm punching the data onto the plate.
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I'm sure that with practice I could streamline the process and improve my success rate, but I've got too many other things on my bucket list for the time being.
By the way, the ID plate is mounted on the glove compartment door, which isn't exactly a secure location, as the door is easily removed, but the vehicle's serial number is also stamped permanently in large characters on the frame of the vehicle, so the serial number on this little plate is really just for convenience.