I've written about this several times over the years; here it is again. I used
to buy defunct beams, and frequent a metals scrap yard to acquire material for
experimental beams. Invariably, the stuff needed cleaning and abrasion of these
quantities was too much work. So I adopted part of a method that was used in my
employer's engineering fab shop to passivate (Alodine) aluminum.
In a nutshell, a strong caustic (lye) is used to attack surface oxidation and
other gunk, after that a water rinse followed by an mild acid wash to neutralize
any leftover lye and a final water wash and drying results in a nice slightly
etched/satin surface.
I do this outside by building a trough out of 2x4s or other scrap lumber lined
with heavy plastic sheet. Make this long enough to handle the longest length of
tubing. I use ordinary household lye that is back on the market now that meth
users can get their stuff from Mexico instead of cooking it themselves. Of
course, I use gloves and eye protection. Experiment with the concentration;
some fizzing should be evident at first. This will subside as the mixture wears
out so you might have to freshen it up. Depending on the alloy there will be
some darkening of the surface but this will wipe/rinse right off. I keep a
garden hose running to rinse the work and to use in the case of a splash onto
me. Ordinary white vinegar of Costco gallon jug variety will finish the process
and help remove any leftover smut. Be sure to rinse with water both inside and
out and you're done.
Dispose of the leftovers carefully. Out here in the desert I just pour it on
the ground; in more civilized surrounds you might want to use it as drain cleaner.
Use this at your own risk.
ps. If you homebrew equipment and build your own boxes a method I've used is to
make everything out of flat sheet with corner blocks. A random orbit sander,
sometimes used with a lubricant, can give a lovely "brushed" surface effect if
followed by etching by the above method. See my QRZ page amplifier photos for
examples.
Wes N7WS
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