Variances in wire dia of same guage

[mkat]

There are variances in wire diameter of the same guage depending on the build and insulation. For example, single build 42 awg may be available in 3 different diameters. I have two spools of solderable polynylon which was sold as 42 awg wire:

- one is 0.063mm
- the other something like 0.069mm

I also have 2 samples of solderable polyurethane which is sold as

- 0.063mm, but the actual diameter is 0.075mm
- 0.057mm, but the diameter is 0.063mm

If these figures are correct for different builds, which is the preferable diameter? I suppose if I was winding to turn count then I'd have to make sure it would fit on the bobbin. How do you normally work around these issues? Also, do you avoid a certain diameter depending on the application?

[Spence]

Manufacturers do have a tolerance to work to. You should expect the diameter to vary in the 3rd decimal. Generally it's such a small difference that it hardly matters. When it does make a big difference you need to make a turn-count adjustment and label your reel so you know to make that adjustment for the whole spool.

[mkat]

Ok, even the variance in the 3rd decimal place will impact the turn count due to the large number of windings. I looked at a chart yesterday and the insulation affects the 3rd and 4th decimal place, which concerned me about the actual sizes as the 2nd decimal place was affected (size claimed is 0.063, actual size is 0.075mm). If a wire is supposed to be 0.063mm without the insulation, then a measurement of 0.063 implies no insulation or a smaller diameter wire. The latter seems likely with the sample wire I have. So, how much tolerance is acceptable?

[Possum]

tolerances....

It doesn't matter what tolerance is "acceptable." You are stuck with what is manufactured and each batch can vary. One thing that I find really annoying personally is that almost every sample of vintage 42 gauge wire all measures .0027" even up to little over a year ago before plain enamel stopped being made in the USA, it was all uniformly the same size and very good stuff. Now REA is the only one making PE in the US and theirs is .00265" small difference but very noticeable difference that I had to change my winds to accomodate the change. So you really can't complain to your supplier because they surely aren't going to run a new batch of wire for you, you either buy what they have or try somewhere else. In the case of PE in the US there isn't any "somewhere else."

[Spence]

Too true Possum. Tends to suggest that Fender encountered problem like that for years when you look at the changes in turn counts the various eras have.

[mkat]

Thanks for your comments on this, I can understand the frustration. One of the sample wires I mentioned above that has a diameter of 0.075mm, is very close to 40 awg (0.0711mm, 0.0028"). Is this significant enough to make an audible difference even after compensation?

[Joe Gwinn]

Ok, even the variance in the 3rd decimal place will impact the turn count due to the large number of windings. I looked at a chart yesterday and the insulation affects the 3rd and 4th decimal place, which concerned me about the actual sizes as the 2nd decimal place was affected (size claimed is 0.063, actual size is 0.075mm). If a wire is supposed to be 0.063mm without the insulation, then a measurement of 0.063 implies no insulation or a smaller diameter wire. The latter seems likely with the sample wire I have. So, how much tolerance is acceptable?

If you hang around the wire manufacturer websites, you will see that with fine wire gages like #43 the manufacturing tolerance is plus or minus 5% on diameter of the bare copper, and so the resistance per foot can vary by plus or minus 10%. I know this sounds terrible, but while winding such fine wire one can easily get 10% to 20% stretch (and thus resistance change), so it isn't obvious why a manufacturer would spend the money to achieve 1% tolerance when it will just be lost in winding.

It doesn't matter which manufacturer's data you look at, as they all are quoting from NEMA-MW-1000, "Magnet Wire", the standard used by all magnet-wire makers worldwide. (NEMA stands for National Electrical Manufacturers Association.)

[mkat]

If you hang around the wire manufacturer websites, you will see that with fine wire gages like #43 the manufacturing tolerance is plus or minus 5% on diameter of the bare copper, and so the resistance per foot can vary by plus or minus 10%. I know this sounds terrible, but while winding such fine wire one can easily get 10% to 20% stretch (and thus resistance change), so it isn't obvious why a manufacturer would spend the money to achieve 1% tolerance when it will just be lost in winding.

It doesn't sound too good that's for sure. So, if the wire can stretch from 10% to 20%, then going for a thinner tolerance will exacerbate the problem.

But, is there an audible difference after compensating for the differences in wire size? Correct me if I'm wrong, but my understanding (which is limited in this area) is that there'll be a change in tone. I don't know if you can compensate close enough for this, or whether it's worth it if the tolerance is way off.

[Joe Gwinn]

It doesn't sound too good that's for sure. So, if the wire can stretch from 10% to 20%, then going for a thinner tolerance will exacerbate the problem.

But, is there an audible difference after compensating for the differences in wire size? Correct me if I'm wrong, but my understanding (which is limited in this area) is that there'll be a change in tone. I don't know if you can compensate close enough for this, or whether it's worth it if the tolerance is way off.

Well, everything affects tone, so some degree. Part of the variation in tone comes from the fact that the insulation thickness also varies, and does so independently of the variation in bare wire diameter.

But, if you wind to a specific turns count, you will have the least variation in tone. Lots of makers have commented that they buy a big spool of wire, run some experiments, and adjust their recipe to get the desired tone given that specific sample of wire. If the spool is large enough, they don't have to adjust all that often.

[mkat]

Well, everything affects tone, so some degree. Part of the variation in tone comes from the fact that the insulation thickness also varies, and does so independently of the variation in bare wire diameter.

But, if you wind to a specific turns count, you will have the least variation in tone. Lots of makers have commented that they buy a big spool of wire, run some experiments, and adjust their recipe to get the desired tone given that specific sample of wire. If the spool is large enough, they don't have to adjust all that often.

Problem solving and workarounds it seems are almost unavoidable.

Thank you all for your replies, it cleared a few things up for me.