# Accurately measuring diameter of very fine copper wire ?

Discussion in 'Electronic Repair' started by N_Cook, Aug 4, 2009.

1. ### Jim YanikGuest

you should not be making the mesaurement if the tool or workpiece is dirty.

3. ### Smitty TwoGuest

Well, he's dead now, so he can't argue the point with you ... but I'd
say if your mic is grimy and gummy, it's not a precision instrument now,
even if it once was.

4. ### spamme0Guest

Sometimes, when a measurement is difficult, it's time to reformulate the
problem.

If your objective is to rewind a coil, take your best shot at wire size
and rewind the darn coil. If the resistance and inductance come out right,
Isn't that what you really want? If not, try different wire.
Self-resonant frequency will give you some idea whether your
winding technique matches the original for capacitance between
layers.

7. ### N_CookGuest

I do so agree, like minds and all that

8. ### Adrian TuddenhamGuest

Make the bundle by winding the wire 32 times around two spaced pegs so
as to be certain that all the 64 wires this produces between the pegs
are parallel and not intertwined. Slip the wire off the pegs and do not
twist it, but squeeze the parallel section so that it takes up a
cylindrical shape.

Wrap another length of the same wire tightly around the outside of the
cylindrical section for a known number of turns (20 at least). Unwind
the wire and measure its length and divide by 20 to calculate the mean
circumference of one turn.

Do exactly the same thing with a length of wire whose diameter you do
know (probably something much larger, so that you can measure it
easily). You may not be able to wrap as many as 20 turns, so adjust
the divisor accordingly.

The ratio of the lengths of the one-turn circumferences will be the
square of the ratio of the wire diameters.

9. ### N_CookGuest

Friday afternoon after a long tiring day yesterday, I cannot
thought-experiment my way into this. I'll have to have a go with some
thicker wire to start with, to work out the method you've outlined

10. ### N_CookGuest

For this very fine wire it is only ever enamelled/lacquered wire I ever
deal with, being used as magnet wire, pick-up coils and the like

11. ### Adrian TuddenhamGuest

I believe some variation of this method was the standard way of
determining the gauge of wires many years ago. It had the advantage
that the reading was averaged over a number of wires (some of which may
not have been exactly circular in cross-section) and, once established,
could be used by anyone with a ruler to give a fairly good degree of
accuracy.

12. ### mikeGuest

I'll skip the lecture on going to insane lengths for no benefit and ask
one question...

Why do you care?

What is it about your application that requires such precision in the
diameter of the insulation?

The obvious solution, and one that is actually related to winding coils,
is to wind 20, 500, how many you feel are needed, turns on a solenoid.
Measure the length of the solenoid and divide by N. You can get
arbitrary precision for THIS spool of wire.

For manually wound coils, the number of turns you can get in a unit volume
is related more to the skill of the winder than the dimensions of the wire.

13. ### kilowattGuest

How about winding the wire onto a piece of 1/16th inch piano wire, do ie; 100 turns and then measure the overall length. Presumed that the wire has no enamel.

My best way.
KW

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.

15. ### N_CookGuest

That applies to most copper wire but not these finest dimensions where
that formula breaks down