On Mon, 30 Sep 2013 14:04:04 +0100, N_Cook wrote:

On 30/09/2013 13:02, tuinkabouter wrote:
On 9/27/2013 3:51 PM, wrote:
On Tuesday, August 4, 2009 10:38:19 AM UTC-4, N_Cook wrote:
Not the first time I've met this problem.
Say nominally about 0.05mm . With a micrometer, how much are you
compressing
it? could easily be out by 20 percent out and squaring that if using
weight
to length via density or resistance calculation via resistivity, is
very
iffy.
If access to a microgram resolution of weighing scales then a few
metres of
the wire and density of copper and allowance for enamelling , but no
highly
accurate weighing machine. Optically comparing under a microscope needs
known diameter standards.
How about a longish length , folded 6 times until 64 wires. Maybe
longer/more bulk. Hand twist together until it will not sensibly
tighten any
more. Take average diameter, use packing factor allowance, and infer
for 1
wire diameter, how better accuracy might that be.?
If I start from known good coil of say 46swg enamelled wire and do
this 64
wire trick , to work backwards, how accurate/reliable would the
manufacture
sizing be ?
Any other ideas?


Take 10 meter. Measure the resistance.
resistance is 0.0175 ohm per meter per square millimeter.
From this you can find the area.
Area is 1/4 pi d*d This will give the real copper diameter.

Two prerequisites. Pure copper and the wire is round.



That applies to most copper wire but not these finest dimensions where
that formula breaks down
I'm a machinist and I measure parts that have features smaller than
the wire in question. I use an optical comparator sometimes for these
measurements. The comparator has a large screen that makes these
measurements easy. However, I also have a small hand held comparator
loupe that is used similar to a magnifier. The difference though is
that this comparator has a reticle that touches the item to be
measured. This helps to avoid parallax errors. Mine is made by PEAK
but there are several other brands available. It has a 10x lens in it
and will accurately measure features as small as .025mm.
Link:
http://www.peakoptics.com/index.php?...oducts _id=12
Eric