On 13 February 2012 21:38, gene heskett <[email protected]> wrote: > On Monday, February 13, 2012 02:24:49 PM Roland Jollivet did opine: > > > ..snip > > > > I would imagine... that the oxide layer is way way thinner than a micron > > in thickness, and while tough as you say, in climb milling the cutter > > tip will hit the metal and with the eggshell effect, simply push past > > the oxide layer. > > In electronics, my specialty, we have a tendency to rate this oxide film by > its voltage withstand capability, which in the above mentioned .001 seconds > is about 40 volts. This insulation BTW is perfect, and is considered to be > degraded if a single electron succeeds in penetrating it. Leave it out in > the 19% oxygen air for a few weeks, or help it along with a hydroxide bath > and it can exceed 400 volts. That is quite a bit more than a micron > although I don't have a thickness/voltage conversion table handy ATM. > > > I think that if this was a general problem, it would receive more alerts > > in industry, although some shopfitting sections which are already > > anodized, do take their toll on the saw blades. > > That has been noted, I've nicely rounded the teeth of several Starret > hacksaw blades on the stuff myself, on one particular piece even breaking > the teeth completely off! So I tend to steer clear of colored alu as raw > material. :) > > > Regards > > Roland > > But.. you can take almost any piece aluminium lying around (not anodised), lightly touch it with the blunt rounded side of two crocodile clips, and you'll measure a few milliohms. What happened to the oxide layer? It's so thin that a few mN of pressure tore through it.
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