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The reason you don't want to use a steel firewall pass-thru conductor
hasn't got a thing to do with steel's tendency to magnetize but rather
because it's a lousy conductor. When you're trying to get enough
current from the battery to the starter, one thing you don't want to
do is waste anything on heating up stuff in the path. Any high resis-
tance link, like a couple of steel bolts, is to be avoided. OK, use
copper pass-thru, if you must - just be sure to provide enough cross-
section to keep the resistance low, keeping in mind that the lowest
resistance is just the cable with no bolts at all. However, if you are
going to use a bolt, use the starter relay connections as a guide to
absolute minimum cross-section (you don't think the manufacturer of
that relay is going to put in one micron more than absolutely
necessary, do you?). As far as magnetic influence is concerned, wires
carrying current produce magnetic fields that are proportional in
intensity to the amount of current. Stop cranking your starter and
the field produced by the cables from the battery to the starter
goes away. That field can be fairly large so to keep it from getting a
permanent hammer-lock on your mag compass, it's a good idea to keep
those cables as far from it as possible. A permanent magnetic field,
such as might be produced by a magnetized bolt or the steel in your
engine mount, by definition is pretty much steady-state and should
be able to be compensated for when you swing your compass.
Oh yeah, if you can get it done without it being ridiculously
expensive, have your threaded copper gizmos silver-plated. In my other
life, I've used copper things for connection points in some very high
current applications and we've found that the silver plate preserves
the low resistance. Time corrodes all (just ask my wife) and silver
corrosion products are as good a conductor as the parent metal while
copper's ain't.
I've noted that different aluminum alloys take on a very different
surface appearance and texture even when done at the same time. I had
made some non-strucural parts out of a hunk I had laying around the
shop and sent them off with the other aluminum bits and pieces to be anodized. I was quite surprised at the look and feel when they came
back. As I have no background in this area, I asked about it and was
informed that what I saw was due to the alloy. Didn't bother me, but
if you're trying for a certain cosmetic appearance, try a sample
first.
Another source of gas struts is ones used on late model Cadillacs
for the trunk assist. Found one of these that was perfect for the
nose gear down-lock when the original gave out. Might be a source for
you guys using them on your canopy.
Cheers,
Dan Schaefer
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