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Accurately measuring diameter of very fine copper wire ?

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.

--
~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk
Reply to
Adrian Tuddenham
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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

Reply to
N_Cook

Why not measure the resistance and calculate the diameter from that? (Assumes the wire is just copper and is round).

Reply to
Pat

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

Reply to
N_Cook

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.

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~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk
Reply to
Adrian Tuddenham

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.

Reply to
mike

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

Reply to
kilowatt

I saw a prototype optical measuring system about 30 years ago that was being refined to measure copper wire on the production line. It was already accurate to under 1/1000 inch, at production speeds.

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

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.

Reply to
tuinkabouter

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

Reply to
N_Cook

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:

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Eric

Reply to
etpm

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