Alternate metals

[JGravelin]

I've been experimenting with 4140 alloy over the last few weeks, which contains both chromium and molybdenum. The chromium definitely gives things a boost, but I'm still in the early stages of critical listening.

If any of you have played with it -or other alloy steels -lets discuss!

[LtKojak]

I've been experimenting with 4140 alloy...

Experimenting... how?

[JGravelin]

I'm playing with some 4140 hexheads screws I found, swapped into a few familiar HB and P90 winds just to see what it does. I haven't been able to find much on the magnetic permeability of it beyond "displays good magnetic characteristics" so far, but was able to research and compare the makeup of 4140 vs 1018 here:

Compare SAE-AISI 1018 to SAE-AISI 4140

Not knowing what the magnetic and sonic effects chromium could have and judging purely off the carbon content and lower iron, I was expecting it to be pretty bright but it's actually not. It seems like it's got potential for something with pickups, but I'm not sure exactly what yet or what the best way to apply it might be.

This has definitely made me curious about other alloys that could be used and I've been reading and trying to educate myself more in all of that. I'm sourcing out some .188 rod and .125 flat of 4140 and possibly a couple others as well to check out for slugs and keepers - I'll admit that I'm pretty interested and curious to hear how they'll perform. One way to find out!

[John Kolbeck]

I think you're better off comparing the permeability and conductivity of these metals rather than just listening to the outcome, going the technical route, because how they contribute to the sound will differ from one pickup to the next.

[JGravelin]

I agree with you, John. As I mentioned, there's limited information out there regarding permeability and conductivity and under such conditions, one does the best that one can. For me that means researching and a lot of reading, comparing ratios of the various elements involved, and not being afraid to take chances and actually TRY IT if it seems like it could be useful.

Would love to hear about experiences with other alloys from those who've played with them.

[J M Fahey]

Not into pickups but make own speakers, so very interested in magnetic properties.
In general, permeability is not such a big deal, mainly because it changes little, unless iron percentage is reduced by some gross value, but hysteresis curve.

Smoothest, less obtrusive, is that of so called "sweet" iron, that one with minimum carbon content and which ideally does not stay magnetized; the opposite end of the scale being Alnico or Ticonal.

4140 , being weapon/tool quality must have a somewhat hard curve, test it by magnetizing a slug and then checking it lifts iron filings.

Personally I avoid that like a pest and use only 1010 if available or 1018 but not higher.

Only concession is turning polepieces from 12L14 bar, because it still is low carbon, and the added lead does not really *alloy* but forms microscopic lead balls which both lower tool friction and make scrap break into short scales instead of looooong curly strips which can clog the lathe and even break a tool tip if it catches.

[salvarsan]

You can get a permeability figure of sorts by testing inductance of a small coil, with and without the screw/slug in the center.
100 or 200 winds of magnet wire on a plastic slug is enough.

This assumes you have some kind of inductance meter; a cheap one is good enough.

I did this to sort my Alnico 5 from A8 slugs when they got mixed together. It was sensitive enough to distinguish between Alnico 5 slugs from different vendors, so you could actually sort screws and slugs to find outliers, if you wanted.

[John Kolbeck]

In general, permeability is not such a big deal, mainly because it changes little, unless iron percentage is reduced by some gross value, but hysteresis curve.

Isn't much of a steel's permeability dictated mostly by it's structure? http://www.scielo.br/pdf/mr/v5n3/v5n3a23.pdf It seems to me that there are some examples of steel that are highly magnetic, and some that don't seem magnetic at all, but maybe I was mistaking some other alloy for steel.

[Mike Sulzer]

You can get a permeability figure of sorts by testing inductance of a small coil, with and without the screw/slug in the center.
100 or 200 winds of magnet wire on a plastic slug is enough.

This assumes you have some kind of inductance meter; a cheap one is good enough.

I did this to sort my Alnico 5 from A8 slugs when they got mixed together. It was sensitive enough to distinguish between Alnico 5 slugs from different vendors, so you could actually sort screws and slugs to find outliers, if you wanted.

The linear relationship between permeability and inductance when using a short open core holds only for low to moderate permeability. That is, you can measure differences accurately with a material such as alnico were relative permeabilities are typically in the single digits, but as the permeability rises, the measured differences get smaller than real. This can be thought of as a result of the high reluctance in the free space path completing the magnetic circuit outside of the material. The electrical analogy is as if you had an extra 10 ohms of resistance in series with your DVM that you did not know about. You could measure a 1K resistor reasonably accurately, but all small resistances would look like about 10 ohms.

[J M Fahey]

Well, it *really* happens, regular cheap meters will always show around 0.5 ohms even with test leads shorted together, that can be ignored measuring, say, 100 ohms and up, but on small values, the typical power transistor ballast wirewound resistors, often 0.33 or 0.47 ohms, (or lower), your precision is ruined.

[salvarsan]

Just as a heads up, the method I described is standard practice in wire manufacture.

Since different wire batches are welded together in a continuous strand for the final heat treatment and run through a coil bore at the end. A change in permeability serves notice that the wire should be cut and put on a different spool. Again, an ordinary coil with a few hundred winds is sufficient for distinguishing between not only different alloys but different melts of the same alloy.

One method is to measure coil reactance at a suitable frequency. Another common one is to use the coil as a variable inductor in a resonant circuit and then test the frequency.