View Full Version : Cutting Alnico Magnets?
Hello...
Have any of you tried to cut Alnico magnets?
I have a pile of long stick magnets I got from somewhere, if I can cut them down I can use them.
Ken
WolfeMacleod
05-12-2006, 07:23 AM
You don't. They will shatter.
Possum
05-12-2006, 09:58 AM
Well yeah you can, you'll have to buy a lapidary diamond saw, the bad news is diamond saw blade for a small 6 inch lapidary liquid lubricating saw are expensive, the saws are expensive. The other bad news is that alnico is really hard material and trashes diamond blades real fast. I think magnet manufacturers use some kind of diamond slurry they buy by the barrel to cut the stuff. There's other ways you could do it, scoring the alnico with a carbide cut off disc in a dremel or Foredom then whack it to break it off but thats pretty crude and you'd have to grind and sand the break to make it acceptable.
I have a band saw from Micromark that will also use a diamond band saw blade with water coolant, the blade costs a hundred freaking dollars....cutting 3 or 4 bar magnets into shorter sections trashed the blade in short time.
Probably more info than you want to know eh? You could also try buying a $99 tile cutting saw at a hardware store, its likely you'll trash the blade in that thing pretty quick but the saws are liquid lubrication and designed to cut stone, I thought about it but never tried that one........Dave
I looked at some 'Harbor Freight' tile saws, one of the cheaper ones that look like little wood saws might work. I looked at the 'big' ones too, I can't afford $400.00+ just for the saw, never mind the blade. :eek: At least I got some good ideas.
Ken
Possum
05-13-2006, 02:18 AM
I'm not sure what kind of blades the tile saws have, they might be carbide or something, but I've seen cheap ones go for $80, you could probably cut a fair amount of alnico rod with one since they're not real thick. I used to cut alot of quartz crystals, their hardness rating is 8, I think alnico is around 12 or something, its very hard material, it was difficult enough to work with quartz and quartz eats diamond grinding plates up real fast. Cheaper to have your magnets cut to size....
An Alnico rod I use is 1/4" diameter tops... I can live with the expense of sawblades if I can get a good result. I wonder if an aluminum oxide wheel will work? When I went to HF to look at the saws, I saw some of their 'diamond sawblades', tiny pieces of diamond in the blades and not very many of them either. Maybe if I used a good quality blade, I would get more life out of them.
It's worth a try anyway,
Ken
Possum
05-13-2006, 01:16 PM
1/4 inch is pretty thick, it might be smarter to score around the rod then break it and grind smooth on a cheap grinder, then sand on a disc sander. Hope this doesn't turn out to be more trouble than its worth, alnico is really hard material.....
David King
05-14-2006, 12:21 AM
I can't say I've spent any time doing this but I don't think the diamond grit wears out quite so quickly, i think there is something in the alnico that must be clogging up the grit.
I know you're looking for ways to cut the magnets on the cheap. However, here is an extract from one site to consider:
"Alnico magnet material is very hard and brittle. On average the materials hardness is 45 Rc and conventional machine tools and cutters are not appropriate. Abrasive grinding and electrostatic discharge machines (EDM) are the typical means of fabrication for this magnet alloy. Most magnet materials are machined in the un-magnetized state. Once the fabrication and cleaning operations are complete the magnet is then magnetized to saturation."
http://www.duramag.com/magnet-materials/alnico/default.asp
According to the above extract, how much will it affect magnetism if the magnets are cut in a magnetised state?
Regards,
Michael
Joe Gwinn
05-22-2006, 01:59 AM
How do the magnet manufacturers do it? They cannot be chewing $100 diamond blades up after four little magnets, and sell yet magnets for a buck or two.
Joe Gwinn
05-22-2006, 02:06 AM
I know you're looking for ways to cut the magnets on the cheap. However, here is an extract from one site to consider:
"Alnico magnet material is very hard and brittle. On average the materials hardness is 45 Rc and conventional machine tools and cutters are not appropriate. Abrasive grinding and electrostatic discharge machines (EDM) are the typical means of fabrication for this magnet alloy. Most magnet materials are machined in the un-magnetized state. Once the fabrication and cleaning operations are complete the magnet is then magnetized to saturation."
http://www.duramag.com/magnet-materials/alnico/default.asp
According to the above extract, how much will it affect magnetism if the magnets are cut in a magnetised state?
Not at all, unless the magnet is heated almost to red heat. Cutting wet will keep the magnet cool. The dust from cutting may be a nuisance, as it will try to stick to the magnet or magnets.
I've been checking on this, and it seems lots of oil coolant is used to keep the alnico cool while cutting, also very light cutting force and a high blade speed is used too. Only after cutting is the magnet charged.
Did anyone ever notice on 1960's Fender pickups the magnets have large cutting marks across the faces? They must have used a sawblade with coarse grit.
Ken
Spence
05-22-2006, 10:23 PM
Why not send them to a magnet manufacturer and negotiate a price to cut them to the lengths you require.
Well, there's a couple of reasons...
1) I asked a couple of magnet vendors to cut them for me, and they weren't interested.
2) If I can cut these with accuracy, I can do the same with mild steel rods for ceramic mag pickups.
3) I can save much $$$ by ordering whole rods, also I can cut my own unground/unpolished magnets to a length I need. Ever get magnets that varied in length in the same bag by .015 or so?
Ken
I've always scored the outside with a dremel and reinforced cutoff disk then grind them. I will also demagnetize them and remagnetize them. I use a large tool demagnetizer to demagnetize and Neo Bars to remagnetize. If you need to make many the exact same length you can get a piece of steel plate drilled and then hardened, leave in full hardened state. The you put the rod(s) in the hole(s) and apply to a sanding disk until the steel hits. The large face of the steel plate will prevent from ginding too far and help keep things cool and holdable. You can do this without first demagnetizing, but remagnetizing might be a good idea.
SlidePicker
05-23-2006, 07:34 PM
quartz crystals, their hardness rating is 8, I think alnico is around 12 or something...
That's on the Moh's hardness scale that goes to 10 (diamond.)
pdf64
05-24-2006, 02:50 PM
Hi, I remembered this from Kinman.com
"42) Can I grind a magnet to reduce it's height?
Definitely not. Grinding or filing magnets will cause irreversable loss of magnetic properties. The magetic material (metal alloy) is carefully heat treated during manufacture to bring out the desired magnetic properties, excessive mechanical vibration and heat can alter or even destroy these properties."
I've never tried it but the above advice sounds worth considering.
Peter
Spence
05-24-2006, 03:21 PM
Simply not true. Why not ask Mr. Kinman to prove what he says.
Mr. Kinman is 'kinda sorta' right...
Grinding a magnet will make it hot in a hurry, and according to my reference books overheating Alnico will permanently demag it. So, I have to find a method
of cutting that will work. Joe Gwinn was right, there has to be a way to do it cost effectively, or buying precut magnets would not be cost effective.
Ken
Spence
05-24-2006, 10:44 PM
I grind AlNiCo to length every day. If you get it cherry red you will lose some magnetism. It's easy to recharge it though with a pair of neo mags. I have also cut AlNiCo rods with a dremel. It takes time but it can be done and then you'll have to grind the surface then to get the exact length and a flat face. You can sand AlNiCo. Just try it. For instant bevelling there's nothing easier than mounting an AlNiCo slug in a drill and spinning it at an angle againt a sanding belt.
Steve A.
05-25-2006, 05:12 AM
I grind AlNiCo to length every day. If you get it cherry red you will lose some magnetism. It's easy to recharge it though with a pair of neo mags. I have also cut AlNiCo rods with a dremel. It takes time but it can be done and then you'll have to grind the surface then to get the exact length and a flat face. You can sand AlNiCo. Just try it. For instant bevelling there's nothing easier than mounting an AlNiCo slug in a drill and spinning it at an angle againt a sanding belt.
Spence- I think that Chris Kinman was referring to a customer trying to grind down the slugs in an existing pickup. And I think that page goes back many years, long before the idea of charging slugs with neo magnets was presented here (I think we all pictured the old Fender factory with that huge machine used to charge the AlNiCo slugs... :eek: Or bringing our pickups down to a machine shop in the seedier part of town.)
Steve Ahola
P.S. I'm wondering about cutting AlNiCo bar magnets to use in a Firebird style mini-humbucker... any luck using a dremel for that?
Spence
05-25-2006, 02:46 PM
Yup, no problemo. done that too. Just be patient, take your time and be prepares for lots of dust from the cutting discs. Oh, and you'll probably get through two or three of those in the process.
I learned something else about Alnico... the cobalt in Alnico is toxic if it is absorbed into your body, so if you are cutting or sanding the stuff please wear a respirator!
Ken
Joe Gwinn
05-27-2006, 05:45 PM
One thing strikes me. Diamond blades are not good for iron alloys, such as alnico, as diamond (a form of carbon) dissolves quite easily in iron. Use aluminium oxide instead.
Possum
05-28-2006, 04:57 AM
in the lapidary industry, like in Brazil they don't use $100 diamond discs you buy for retail. they use industrial diamond dust slurry and metal blades, you can't buy diamond dust retail, at later stages they use carbide slurry, same method. I've cut bars with my diamond water cooled band saw but after about five cuts the blade is just about shot. For rods they are a quicker cut to do being smaller, the water cools and lubricates and washes away the dust. In the old days some guys cut rocks without water or coolant, you have to wear a good mask, some minerals do real bad things to you. I forgot what mohs alnico is but its real high. I looked at some tile saws today don't know what abrasive is in the blades, a larger blade is better, they had some there for about $50, cheap chinese stuff I guess....for cheap you could do what Spence does, score with a cut off disc and dremel break the score and grind and sand the ends.
Spence
05-29-2006, 09:07 AM
You can cut right through the AlNiCo with a dremel cutting disc which is what I do rather than scoring them around the edge. I would be a little concerned about the alloy's brittleness to try scoring and snapping. In any case, Dremel cutting discs cost peanuts so it's less of an issue than anything with diamond dust/slurrey. The trick is to be patient because the Dremel discs can shatter very easily.:torch:
Joe Gwinn
05-29-2006, 11:06 PM
in the lapidary industry, like in Brazil, they don't use $100 diamond discs you buy for retail. They use industrial diamond dust slurry and metal blades, you can't buy diamond dust retail, at later stages they use [silicon] carbide slurry, same method. I've cut bars with my diamond water cooled band saw but after about five cuts the blade is just about shot.
Right. You cannot use diamond to power-grind iron alloys, even with water cooling. What happens is that at the point of contact between abrasive particle and metal, the temperature is very high, and the diamond simply dissolves in the iron. This is well-known in the metalworking industry.
Diamond works OK for wet hand grinding steel, if one isn't too aggressive.
I forgot what mohs alnico is but its real high. I looked at some tile saws today don't know what abrasive is in the blades, a larger blade is better, they had some there for about $50, cheap chinese stuff I guess... .
Alnico is probably about 7 or perhaps 8; it cannot exceed diamond, which is 10. Pure cobalt is 5.5 Mohs. Alnico can be ground by aluminum oxide (9 mohs) and silicon carbide (9-10 mohs).
Anyway, a blade using aluminium oxide and/or silicon carbide, cooled with water or soluable oil, ought to work just fine. One can use a soft metal blade and an abrasive slurry in a bandsaw-like saw. A lapidary saw with an aluminium oxide blade ought to work.
Thank you...
Until now I had no idea that diamond will actually dissolve in iron based metals. I looked it up in my chemistry and machining books, and you seem to be right. Diamond is a form of carbon, and iron type alloys (like Alnico) when heated absorb carbon readily. So now I'm looking for an aluminum oxide blade. I bought a diamond blade already, I'll use it to test a saw. Now I'm looking for an 'oil' type
coolant pump too...
Ken
David Schwab
05-30-2006, 03:39 PM
I learned something else about Alnico... the cobalt in Alnico is toxic if it is absorbed into your body, so if you are cutting or sanding the stuff please wear a respirator!
Nickel is also toxic. And Aluminum deposits in the brain are thought to be one cause of Alzheimer's Disease.
Always wear a respirator anytime you make dust!
Joe Gwinn
05-31-2006, 02:49 AM
Nickel is also toxic. And Aluminum deposits in the brain are thought to be one cause of Alzheimer's Disease.
Always wear a respirator anytime you make dust! Life is easier if you always cut wet. The cutters work better too, as the fluid keeps the business end cool.
Now, does anyone know where to get a halfway decent thin aluminum oxide cutting wheel? I looked a Harbor Freight, and what they had didn't look very good. I'm looking for a 6" or 7" wheel with a 5/8" arbor hole.
I never thought diamond wheels would be easier to find than aluminum oxide ones.
Thank you,
Ken
I will also demagnetize them and remagnetize them. I use a large tool demagnetizer to demagnetize and Neo Bars to remagnetize.
about remagnetizing with neo bar i ask a magnet company about that a long time ago and here was his answer.
did someone notice a difference with a gaussmeter?
As for the magnetizing Alnico magnets wit Rare Earth magnets you could do it using the size that you outlined 3" x 1/2" x 1/2". Only thing that I would like to point out doing this way you do not SATURATE those magnets using this method of magnetizing. Even using two of Rare Earth magnets and placing Alnico magnet in between you still do not get the full saturation in same way as using DC Discharge magnetizer.
I notice an initial INCREASE in gauss after remagnetizing or reversing polarity. I think this is probabl;y due to the fact that I start with a charged magnet and it doesn't fully demagnetize. I will also say that I have seen reference to magnetizing using other magnets on magnet manufacturers sites.
I notice an initial INCREASE in gauss after remagnetizing or reversing polarity. I think this is probabl;y due to the fact that I start with a charged magnet and it doesn't fully demagnetize. I will also say that I have seen reference to magnetizing using other magnets on magnet manufacturers sites.
thx sk66
very interresting, I think that I will build myself a gaussmeter (with the new A1323LUA Allegro hall-effect) and make some test... also I remember that I used to have a tape demagnetizer in the 70's where did i put that thing?
Possum
06-10-2006, 01:57 PM
in my experience when you charge an alnico magnet it always charges up high and quickly stabilizes at a lower level, has nothing to do with switching poles or what charge it had before, it just can't hold that higher charge and dissipates it. You can also degauss alnico down to about half its charge and over a week or two because the charge is so weak the magnet will not be able to maintain its charge and will degauss almost all the way.......fun with Mr. Science.....
I had a huge demagnetizer once myself, I am going to look in my storage area and see if I can find it. I'm not really sure, but I think the neo magnets will charge up but don't really saturate a magnet like a 'DC' magnetizer because the DC discharge is a huge all at once pulse of power, which 'shocks' the magnet into saturating.
I used to have a 1950's Hammond organ years ago, I remember reading on the back of it that if you wanted to test one of the pickups in it, you were not supposed to use an ohmmeter. This is because supposedly the current flowing through the pickup coil from the meter would demag the magnet. I'm thinking about passing a low DC voltage thru a pickup winding and see if this really works.
Ken
ohmwiz@yahoo.com
Actually, this makes sense. Passing current thru a coil will create an electromagnetic field, getting the field's polarity correct will be key in "charging/discharging" an alnico slug within the field. I would be very surprised if an ohm meter has enough current to do anything to alnico.
David Schwab
06-15-2006, 04:35 PM
Bartolini used to advise not to use older style analog VOM's... they said it might damage the coil. The newer digital VOM's are a lot safer.
I have a couple of real 'old school' VOM's here, one has a 221/2 volt battery
for ohm readings. I imagine that may have enough oomph in it to demag a coil wrapped magnet.
I got an idea for an electric 'dunstunner' from my old organ - I have a big bulk eraser, a variac, and a big rectifier bridge. Maybe if I feed the bulk eraser with known quantities of DC, I can demag magnets to spec. Any ideas?
Ken
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