Dropping permeability of (1018?) fillister head 'bucker type pole screws

[fieldwrangler]

Folks -

Anyone have a fun way to make this happen?

Bob Palmieri

[Helmholtz]

The AC permeability of steel drops with increasing DC (permanent) flux.

[fieldwrangler]

The AC permeability of steel drops with increasing DC (permanent) flux.

Indeed! I like your take on "fun." I mean... a battery & pot on the axe, cap to block the DC from the signal path, we could have a New Control here!

To be more specific, I'd like to drop the permeability of some conventional plated 'bucker screws to cool out a customer who thinks a couple of strings have too much output even with the screws recessed as much as possible with this particular design. I suppose I could maybe find some higher carbon screws but they might not look the same...

[Helmholtz]

You may cut the screws. A shorter screw that doesn't touch the keeper will be less sensitive.

[fieldwrangler]

You may cut the screws. A shorter screw that doesn't touch the keeper will be less sensitive.

Well... in "this particular design" there's no keeper, and in fact the screws don't even contact a magnet. Reduced permeability is actually a good idea in this case.

[Helmholtz]

A shorter screw means less effective permeability.

I would help to know the PU construction.

[fieldwrangler]

A shorter screw means less effective permeability.

I would help to know the PU construction.

Man... I hate being in this position. I did this design for a client, and I have investors overseeing many aspects of my actions these days; can't tell you more about this application. This is especially wrenching for me, since I feel like you're one of the most knowledgeable people on this forum, and I've benefitted greatly from your posts.
I'll do what I can to resume posting info that I consider valuable, but for the moment... just wanna know how to knock down the permeability of existing common fillister head screws if practical. Otherwise, I think I'll just find a way to make higher carbon screws look similar enough... hope they're already plated...

[David King]

Bob,
Could you drill out the screw from the bottom on a lathe? (I'd be happy to do it for you). What about raising the output of the surrounding screws somehow?

[LtKojak]

IIRC, Mojotone offers filister screws in 1022, 1018 and 1010 alloys, both long and short.

Sorry if it's captain obvious talking here...

[Helmholtz]

just wanna know how to knock down the permeability of existing common fillister head screws if practical.

I mentioned the (admittedly unpractical) DC bias method for the only reason that I can't think of a way to reduce the permeability by any practical treatment. It is sometimes possible to increase permeability by heat treatment (annealing), meaning removing internal stresses. But AFAIK it doesn't work the other way round.

Otherwise, I think I'll just find a way to make higher carbon screws look similar enough... hope they're already plated...

Have you verified that higher carbon screws significantly reduce sensitivity?
I compared 1008, 1010, 1018 and 1022 screws in the same PU side by side. While there were changes in attack, feel and perceived treble content, the relative loudness did not change noticeably.

I also measured the inductance values @100Hz of a P-90 design with different sets of screws and found the difference between 1010 and 1022 steel to be around 2%. Of course there is this huge air gap.

[SoulFetish]

I know of no practical way to change the permeability of a material in the way you’re asking about other than changing some physical characteristics. One sure way to reduce the effective permeability in to introduce an air gap. You could accoplish this by splitting those particular screws into two parts. Cut each lower section with a slotted screw slot. That way you can keep your original length and aesthetic.

[Helmholtz]

Don't forget that PUs are no closed magnetic circuits. They typically have an effective air gap (being the average flux path through air) of several cm. For this reason the influence of the permeability of the polescrews on inductance is relatively low.

[fieldwrangler]

Folks -

Thanks for real for this. Dave % SoulFetish - the idea of removing material from the screw sounds very appealing.

Pepe - thanks for reminding me about the various screws available from Mojotone - this will have much relevance to a project in the near future.

Helmholtz - that is some very valuable research, and I look forward to experiencing this effect in a test setup after I get an assortment of screws.

[SoulFetish]

Don't forget that PUs are no closed magnetic circuits. They typically have an effective air gap (being the average flux path through air) of several cm. For this reason the influence of the permeability of the polescrews on inductance is relatively low.

Good point! I wonder if it would have any audible affect (effect?...whatever)

[Helmholtz]

I wonder if it would have any audible affect (effect?...whatever)

Depending on PU construction a shorter or "interrupted" polescrew will lose some ability to focus the magnetic flux and the permanent field at the string will be lower. So it might reduce the string signal output.