good source for steel or iron machine screws for magnetic pickup pole pieces?

You need to read a little bit more about metals and magnetism. Those zinc screws are made of carbon steel. they only have a thin coating of zinc plated on (also called "galvanized") to keep them from rusting.

If you are not conducting the magnetic flux well, it's not the screws' fault, it's your magnetic circuit design.

(unless you accidently grab stainless steels instead of zinc plated ones).

Tho

Like Tho says, zinc, chrome or nickel plated screws are fine - I use them - but stainless steel as found in screws is not ferromagnetic and will not work. If in doubt, take a small magnet with you when you go to buy them, and check that what you are getting is ferromagnetic.

Tony D

Thanks for both your replies...

The screws are definitely magnetic - I have a Radio Shack 'rare earth' magnet, which is pretty strong and sticks to the screw like glue.

The problem is that the other end of the screw isn't picking up the magnetism - a 2nd screw doesn't stick to it too strongly.

However a regular guitar pickup, say a single coil from a strat, has a magnet underneath the pole, and a screw sticks to the pole pretty good.

Why isn't the magnetism traveling down to the other end of the screw?

Thanks aga> "Mad Scientist Jr" wrote in

messagenews: snipped-for-privacy@p77g2000hsh.googlegroups.com...

It might be the way you have the magnets arranged. I have tried various configurations, and some leave more magnetic strength at the top of the pole pieces than others. The pole side of the magnet has to be touching the iron pole piece, not one of the "neutral" sides.

Tony D

Um... the pole pieces on strat and tele pickups ARE the magnets. Now, a P-90 is as you describe.

--Fletch

Some strat pickups, usually but not always cheap, have iron pole pieces and a ceramic magnet. On a very few (Bill Lawrence?) they are adjustable. I have converted standard alnico-slug-type plastic-bobbin strat pickups to adjustable pole piece with ceramic magnets.

Tony D

If they stick to a magnet they're steel, (and only zinc plated) Guitar signals are small, you won't find better mild steel screws.

I've never seen (solid) zinc screws in a hardware store that'd be a speciality item. Zinc-plated screws ar very common however.

Bye. Jasen

Or maybe better, use long poles and have them touch all along the side of the magnet, which may not be possible, depending on the pup design. If it's a single coil construction, using two slim magnets touching on either side of long poles may be a possibility. For a humbucker, use a center magnet with long poles down either side.

For a pup redesign, I once used simple black mashine screws from a mashine parts toolshop with good results. I chose flat headed screws with a rather small allen wrench hole designed for recessed mountings to have a somewhat large diameter pole piece under the strings. YMMV...

If I understand you correctly, that's what I do. The pole pieces are screws that project below the bottom of the coil in a brass plate, and the magnets touch from either side, with the pole same pole facing inwards - eg North in towards the poles.

Works well for me.

Tony D

Yup, seems we agree on the howto, except it seems you force two same poles (i.e. north-north) against oneanother (with pup poles in-between). If that's correct, I don't understand why, as two same poles will do all they can to counteract one another. I'd use magnet1_north--pup_poles--magnet2_south. If you do do as you state, the weakened magnetic field might still be strong enough, and even be part of a tone and response you like, designed or not, science or no science :-D

Do you have this design adjusted somewhat close to the strings, and in which position, neck/mid/bridge?

This is a strat type pickup we are talking about, and it works well as I described it. - You have the pole piece mounted in a non-ferromagnetic plate (important, eg brass), and force the two same magnet poles into opposition to each other with the end of the pole piece between them. The result is a magnetic attraction at the opposite "working" end of the pole piece which seems to be something like the **sum** of the two magnets used, any way, it is fairly powerful by pickup standards. I just went to my workshop and tried it in a jury rigged set up with a short iron bar and a couple of small ceramic magnets, just to be sure I was right. I am, try it and see. Other configurations I tried gave a weaker attraction at the working end of the pole piece.

I also plan on experiment with a "National" type single coil set up where the magnets are mounted under an iron plate into which the pole pieces are mounted. The magnets have the same polarity **up**, eg north, not inwards. This is how my Lollar "Chicago" pickup is made, but my attempts so far have resulted in a very weak magnetic attraction at the working end of the poles - I need try some more.

Tony D

I tried this yesterday - I took two radio shack "rare earth" magnets

and stuck one to the bottom of the screw (the end opposite the head), then I took a 2nd one, and stuck faced its pole towards the like pole of the 1st magnet (so they repulsed each other), and stuck it to the opposite side of the screw (evidently its attraction to the screw was stronger than its repulsion from the magnet on the opposite side of the screw). A 2nd screw stuck to the head of the screw, although not as strongly as I would have liked (not nearly as strongly as the 1st screw stuck to the magnets). I did try turning one of the magnets around so the south pole of one faced the north pole of the other, and in this configuration, a 2nd screw did not stick to the head of the

Probably (as everyone has said) these are zinc-plated carbon steel screws. Can someone tell me if it would be a better idea for me to somehow permanently magnetize the screws themselves and use them as the magnets instead of placing a magnet underneath? I recall reading a science book as a kid some way to magnetize a nail by attaching a wire from a 12v dry cell and coiling it around the nail but I don't recall the details. I would want the screw to be more or less permanently magnetized - not have to "recharge" it every couple of years - and be a strong enough magnet to serve as a good guitar pickup pole.

If this isn't possible, any advice on better placement of the magnets or better magnets to use? I would prefer an individual magnet per pole piece.

Any help appreciated...Thanks again.

Don't think you'll be able to provide enough magnetic field strength this way to magnetize the screws even to the force your magnets will provide - by far. Sure you're lacking magnetic force? Could be your winding technique.. Lotsa magnet force may not be that desireable; you might end up finding you'd have to lower the assembly a good deal to avoid pulling strings. Of cause, I don't know your design, so...

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### screw

I was thinking of the same. Neodynium magnets are available in rod shape too, so it's possible to use them like old style iron magnet poles. Only, being quite forceful as the are, I don't know how much they'll interfere with one another. Maybe having them touch onto an iron plate underneath would do.

What is "mild steel"? Any idea where to find machine screws (4-40x1-1/4 round or flat head, with nut) made with this?

Regarding the ascii diagram below, showing the piece of iron underneath - how does this work? Does the iron bar extend the magnetic field to a wider area?

Thanks...

Also I would suggest putting some iron or steel on the exposed surface because of the way some neodymium magnets seem to disintegrate, especially if they get chipped. I would prefer to imbed the magnet (and maybe coil) in epoxy, with just a piece of iron or steel sticking out, since that would be robust and less prone to weird disintegration.

Chris

Dunno what was really meant, but since mashine screws often needs to carry some load/torque, and thus be quite strong/hard, I'd guess mild steel simply means steel without the carbon component. What you'd really be after might be the type of soft iron used in i.e. tranformers. Again, dunno what it's called in expert circles. You can create soft iron from non-carbon steel by heating it to glow temperature, IIRC.

You know, poles doesn't have to be round, so another idea might be to call some shop repairing electric motors or building transformers, and obtain some of that soft iron in sheet form. cut it in strips, and laminate those with lacquer to form square shaped poles. Note that in a laminated constructon, you'll most likely obtain the best magnetic capabilities when keeping the strips isolated from one another, else you may have problems with eddie currents.

Your choice of screws is a matter of easy availability plus some adjustability, I'd guess, no? If you finesand the finished square poles, you can make them glide up and down with some applied force for adjustability, if need be, thiugh once you have worked out the formula, you may not need adjustability.

Welcome to the world of science ;) (nope, I'm not a scientist, just electronics educated). You'll most likely quickly find yourself digging through books of theory for understanding induction, capacitance, magnetic forces, hysteresis, saturation in magnetic cores (though the latter is hardly applicable to pups, it's good understanding it) eddie currents et al... This is what other puppie designers have gone through, plus lotsa experiments.

Mmnn, mashine tool shops, maybe?

a soft kind of steel, hacksaw blades are made from carbon steel tie wire is made from the softest mild steel. most bolts and screws are made from steel if intermediate hardness.

yeah sort of

Bye. Jasen