Accurately measuring diameter of very fine copper wire ?

In my analytical work on failed electronics, I would take a wire like that and mount it vertically in a mounting medium that is used for cross- sections. I would mount several samples near to each other. Then I would cross-section the mount and measure the diameters using a microscope with a calibrated filer eyepiece. The diameters with/and without the coatings would be provided to the customer along with an average value.

At the time I was doing it, my lab would charge about $100 for that. Depends how important it is to you for spending that much. Since I am retired, I'm sure it's more expensive now.

Here's a thought...

If you could find a table of resistance-per-unit-length for various wire gauges, and had an ohmeter that could accurately read low resistances...

Fender used 42 AWG and 43 AWG. If this is about rewinding that Landola pickup I wouldn't get too scientific. I would browse the Stew-Mac site and look at what they have to offer. Maybe there is an equivalent supplier on your side of the pond.

You only need two things:

1. A toolroom micrometer (not to be confused with a homeowner mic, or a machinist's shop mic.)

1. The skill to use it.

I can't think in fractions of a millimeter very well, but a good toolroom mic will read directly to 0.0001", and inferentially to

0.00001" within +/- 0.00002" or so.

The trick to not "crushing" the wire is to use the wire like a feeler gauge, between the jaws of the mic., closing the mic slowly while feeling for friction.

We buy 42 AWG single poly for guitar pickups, and order it specifically as "min to nom." (minimum to nominal diameter.) The supplier checks his stock with a toolroom mic, and ships only those spools on the low end of the tolerance range. We verify it before putting it to use.

I thought getting good contact would be a problem. Soldering might work.

If you could not get an optical scale, perhaps a printer could be used to make a scale.

600 dpi would be less than .04 mm.

greg

I would like to email directly and discuss winding guitar pickups. Please email: robert DOT a DOT macy AT gmail DOT com

Where do you buy 42 Awg wire?

We buy small quantities of 30-36 Awg at exceptionally competitive pricing from Fay Electric Wire Corp. (800) 245-9473 752 North Larch Avenue Elmhurst, IL 60126 [not associated with them, or gain by posting this.]

Robert

make a scale.

Interesting idea! I need an inexpensive optical scale from time to time.

I have some 8.5 by 11 inch thermally stable paper printed in Switzerland that has 300 lines per inch printed diagonally on it. Yes, that's 150 black, 150 white per inch. Got 10 sheets at the bargain price of $300 per page and these were 1980 prices.

In a printer doesn't the single blop of ink/laser powder spread out over more than 3 to 4 of those pixels? Does gray scale modify the density? Or, do printers still use those pseudo patterns to generate gray scale?

Is there anybody out there to try this, look at it under a microscope, and let us know?

Robert

On Aug 4, 10:38=A0am, "N_Cook" wrote: [about measuring a small copper wire]

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Measuring microscope. Either a standard microscope with a micrometer-driven stage and a crosshair reticle, or a microscope mounted on an X/Y translation mechanism (calibrated, of course). It's a standard item in instrument shops, and you can measure the width to whatever edge-detection limit your microscope has.

If the length is long enough, resistance and length will do the same trick, BUT resistance measures average resistance (average of radius squared), not average of radius.

One uses a "4 terminal" ohmmeter. To do this easily, use one DVM on ohms and connect it to as second DVM on current to measure the 'ohms current' ; it is usually an even current like 1mA , 10mA etc. Note the value. Then connect the ohmmeter to the ends of the wire under test. Take the second DVM on mV and measrue the voltage across a precise length of the wire under test. Since that is a voltage [high impedance] measurement, contact resistance has relatively little effect on accuracy. One should also take into account the temperature, then plug it into the resistance formula and arrive at the area then reduce that to a diameter.

Neil S.

Get a magnifier with replacable reticles:

If your wire is microscopic and too small for a 8x or 10x magnifier, get a reticule (or graticule) for a microscope:

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

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Yes for the Landola pickup, the number of turns from measuring wire diameter then weight/weighted circumferences and also by the 7.7Kohm ,assuming both pickups are the same then this gives the same number , but does not agree with counting a sample 1000 turns and ratioing , they were in fact laquered together to defeat counting-off

For 2 reels of enamelled wire labelled as 2.4 thou/mil and 2.8 thou/mil and my micrometer that has a 2Kg closure force (just checked via spring and kitchen scales) before the torque clutch disengages. I have to DIVIDE the reading by 1.15 for the 2.4 thou wire and 1.25 for the

2.8 thou wire. I suppose this is to do with the enamel thickness and the wire is specified as the metallic diameter. I assume my wire gauge v wight/resistance tables are for bare copper, not actually specified.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I would like to email directly and discuss winding guitar pickups. Please email: robert DOT a DOT macy AT gmail DOT com

Where do you buy 42 Awg wire?

We buy small quantities of 30-36 Awg at exceptionally competitive pricing from Fay Electric Wire Corp. (800) 245-9473 752 North Larch Avenue Elmhurst, IL 60126 [not associated with them, or gain by posting this.]

Robert

I have emailed to you

I wind 100 turns of fine gauge wire on a smooth rod and measure the length with good calipers, then divide by 100. If there isn't enough for a good measurement, wind 200 turns.

Or spend $50,000+ US for a precision optical measuring machine made to monitor the diameter of wire as it is made or spooled.

--
You can\'t have a sense of humor, if you have no sense!

Tightly, of course.

There's a story that Edison asked a young man (presumably an apprentice) to measure the volume of several light bulbs. The apprentice stated with a ruler, a pair of calibers, trying to get precise measurements so he could calculate the volume. When Edison saw him fussing around, he grabbed one of the bulbs, filled it with water, and dumped into a graduate. I suspect the whole exercise was intended to make a point, rather than measure the bulbs.

Unfortunately, I can't think of an equivalent "clever" way to indirectly measure the wire's diameter.

They were in fact laquered together, hopefully in a vacuum chamber, to keep them from buzzing.

There's always a way. Measure out a long length of wire such as 100 meters. Carefully weigh the 100m of wire. The density of copper is

8.92 gm/cm^3. The rest is math, which I won't attempt without my morning coffee blast.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Jon,

Could not reply to your email, so replying here:

Thank you. MWS is our second choice and first choice for very small gauge wires, like 54 Awg wire They have a wealth of technical information. Regards, Robert

If the coil has been covered in lacquer, then repeated soakings in lacquer thinner should remove the lacquer that was used to bind the coil.

Some careful, light brushing, and agitation could speed up the removal. It should become apparent when the lacquer has been removed as all of the windings will be loose, and a final rinse in clean thinner should be enough to remove any traces.

It would probably be helpful to have a jig/form handy to place the coil windings on, something like two spaced dowels about the same size as the inside dimension of the coil, mounted to a piece of wood or other material. Then with a center point located between the dowels, the coil would turn fairly easily for counting turns.

-- Cheers, WB .............

Unfortunately, if you don't know what the insulation is, you don't know squat.