PDA

View Full Version : Drilling a Magnet



GRH
12-24-2009, 07:21 PM
Hi all
First wishing you all a very merry Christmas and a prosperous New
Year.

Now I need to drill a 5/32" hole thru 2 magnets that are about 5/16
thick.

Is there anything special I need to know ???????????

Am considering using a center cutting carbide end mill so the chips
do not get stuck on the cutter.


Thanks again
Graeme

websterz
12-24-2009, 07:31 PM
Ummm...don't know if it's going to work or not. What kind of magnets are we talking about?

lakeside53
12-24-2009, 07:32 PM
What's the magnet made off? metal or "ceramic"?

lane
12-24-2009, 07:34 PM
cant be done

lakeside53
12-24-2009, 07:40 PM
I bet Evan can do it:D

uh oh... now I've gone and done it:p

Evan
12-24-2009, 07:44 PM
It will reduce the field strength. I am going to try it though but right now I am barbecuing 2 inch thick prime rib steaks in -25 weather.

Later... :D

beanbag
12-24-2009, 08:12 PM
many if not most common magnets are of a very hard ceramic-like material. You will ruin a HSS bit while putting only a small dent in it. Dont' know if carbide will fare much better.
You might have better luck using a grinding like action. For example, one of those little cylindrical diamond coated dremel grinding bits

Black_Moons
12-24-2009, 08:12 PM
Ceramic and neo magnets would probley be the two hes considering..
Id consider something abrasive like a diamond coated hole saw:
http://richontools.com/images/categories/048161.jpg
Iv seen small sets of these on sale for like $20~
Or maybe a masonary bit.. with little pressure, water and a LOT of time.
Ceramic and neo magnets are exceptionaly brittle, and while I havent drilled them id suspect rather hard.


If its just one of those rubber flexi magnets, likey anything will drill through it, maybe pin it beween two peices of wood to prevent it from snaging as it drills through.

smiller6912
12-24-2009, 08:28 PM
I would try one of these:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=32351

Evan
12-24-2009, 09:29 PM
Well, that was a relatively trivial exercise.

I used a specially sharpened micrograin carbide bit left from a broken 1/8" Garr carbide cutter. By using a very long point with two flutes it minimizes the heat buildup with is an enemy of NIB magnets and cutting edges. I ran the drill press at about 100 rpm and used WD 40 as lube. The magnet was held in a pair of vise grips just tight enough to keep it from slipping.

It drills like hard cast iron except the swarf isn't going anywhere. In fact it may just stay attached to the magnet forever.....

http://ixian.ca/pics7/maghole.jpg


I would be careful not to to generate any fumes while doing this. I have a funny feeling that the compound is toxic, possibly very toxic. Use low speed and wet lube. Wash hands after.

hssmike
12-24-2009, 09:38 PM
Merry Christmas everyone !

Evan,
Nothing like drilling on a full stomach :D


Mike

Black_Moons
12-24-2009, 09:42 PM
Evan: Oh yes a specaility ground cutter... lol. Any details on how it was made if thats you're solution? :)
Kinda cool regrinding one of those tiny burrs however, never thought about it before, but you can get packs of em for like $5

to get rid of swaff from a magnet I find that a brass brissle brush works, just violently brush it in swinging strokes, like you where spanking a kid, seems to managed to fling the swaff fast enough to prevent it from flying back onto the magnet. Paper towels can also kinda work but don't seem that effective.

Evan
12-24-2009, 09:45 PM
I just looked up info on the NIB alloy. I was right. It is very toxic and the alloy is very flammable as well. If it catches fire it burns like misch metal, hot and fast.


That might work for regular swarf but this swarf is magnet swarf. I can't even pinch it off the corner.


Kinda cool regrinding one of those tiny burrs however, never thought about it before, but you can get packs of em for like $5


Not Garr you can't. Garr cutters ar 5 to 15 bucks each but they are much harder and sharper than cheap carbide tooling.

Black_Moons
12-24-2009, 09:57 PM
Woah never knew it was toxic. Or that it could sustain itself burning.
Learn something new every day... and good thing too, Or I would be bored out of my mind.

lakeside53
12-24-2009, 10:16 PM
I just knew Evan could do it...:p And.. on Xmas eve ... If I went down to the shop tonight, the door would be locked behind me.. hey...

Merry Xmas to all:o

Black_Moons
12-24-2009, 10:26 PM
lakeside: thats when you come back with the drill and tell your wife the lock was acting up so you drilled through it to avoid hasseling her to open it. :)

EVguru
12-25-2009, 03:59 AM
Blu Tack works pretty well for removing swarf from Neo magnets.

gnm109
12-25-2009, 05:44 AM
I suspected that Evan could do it as well! Neat trick. I'll add it to my list of things that are beyond my limited capabilities but which I admire greatly. LOL

Merry Christmas to all! :)

Evan
12-25-2009, 06:32 AM
Now I am trying to figure out what uses I have for little magnetic wheels...

Weston Bye
12-25-2009, 07:48 AM
Now that you've succeeded in drilling a hole in the magnet, you will want to seal the exposed surfaces. Neodymium oxidizes over time and eventually will crumble to powder. Most Neo magnets are nickel plated but even a good layer of paint or other sealant can be used. No such precautions need be taken with other magnet material.

Magnet manufacturers don't drill holes in their magnets, rather they cast or sinter the magnetic materials to blocks, tubes, rods or balls. The magnets are then sawn to shape with diamond saws and if more precision is needed they are then surface ground. After plating then they are magnetized.

For prototype use I have demagnetized, ground and remagnetized Samarium Cobalt and ceramic magnets, but not Neo. For low force applications, bonded nitrile ferrite magnets (refrigerator magnets) can be easily drilled and machined and pattern magnetized with multiple north-south pole patterns.

POLAR10
12-25-2009, 07:37 PM
NIB magnet are plated to prevent oxidation. They will corrode and turn to dust if exposed to the atmosphere, so replate or reseal the surfaces.

Samarium Cobalt magnets do not need to be plated.

Be careful with the heat generated while drilling since NIB max. sevice temperature is 300 Deg. F and Samarium Cobalt max. service temperature is 660 Deg. F. Alnico depending on grade, the max. service temperature is 840 to 1020 Deg. F.

With Cast Alnico we try to cast the holes, but some customer designs just do not not lend themselves to cast a hole and still have a viable casting so EDM is used to put a hole(s) in a magnet.

Yes, rare earth materials do burn. The powered material is processed in an inert atmosphere to prevent ignition.

Evan
12-25-2009, 08:04 PM
I was vaguely aware of the fire risk which is why I ran it very slow. Misch metal is made from a similar combination of metals and it burns extremely well. That is why it is used to make lighter flints.

I know about the plating and oxidation problem. If I need to drill more I will indeed give them a soak in some laquer.

Incidentally, the max service temperature varies over a wide range for NIB magnets depending on the grade.

beanbag
12-26-2009, 03:49 AM
What's the big deal with the service temperature? So you will degmagnetize a small area near the hole. But it will re-magnetize as it cools back down thru Tc because there is a field nearby from the parts that haven't over-heated.

I think... but not sure.

Evan
12-26-2009, 07:23 AM
As I said, it will lose some field strength, and not just from the removal of material.

If a local area is demagnetized by exceeding the curie temperature in any magnet when that area cools it will be remagnetized by the remaining still magnetized volume, but not to the original value. In order to fully magnetise a material takes a field strong enough to take the material over the permeance knee. The stronger the magnet per unit volume the steeper that knee is and the greater the magnetizing field must be in excess of the resulting permanent field.

Peter.
12-26-2009, 08:49 AM
Blu Tack works pretty well for removing swarf from Neo magnets.

That's what I used to use when I had a job as a teenager making development brushless DC motors. Also works great for getting grinding dust and swarf particles out of mobile phone speakers.

kyfho
12-26-2009, 06:09 PM
Not familiar with Blu-Tack, but I have had very good luck removing chips and swarf from neo magnets with a simple, repeated application of good tape, ie. duct tape or painter's tape. Anything sticky that doesn't leave a residue behind.

Evan
12-26-2009, 11:15 PM
Yeah but, this is swarf from the magnet. The swarf is neo magnet dust stuck to a neo magnet. It's stuck on there like fine weld spatter. I think maybe the best way is to goop up the magnet with some silcone sealer and then pull that off.

bborr01
12-27-2009, 01:30 AM
As I said, it will lose some field strength, and not just from the removal of material.

If a local area is demagnetized by exceeding the curie temperature in any magnet when that area cools it will be remagnetized by the remaining still magnetized volume, but not to the original value. In order to fully magnetise a material takes a field strong enough to take the material over the permeance knee. The stronger the magnet per unit volume the steeper that knee is and the greater the magnetizing field must be in excess of the resulting permanent field.



Couldn't have said it better myself.:D

Brian

12teethperinch
12-30-2009, 01:18 PM
May or may not be helpful, but lee valley sells ones with holes in them already http://www.leevalley.com/wood/page.aspx?c=1&p=40075&cat=1,42363,42348
Darrell