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Is it safe to drill out a rare earth magnet?

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Forum topic by Jonathan posted 605 days ago 2311 views 0 times favorited 15 replies Add to Favorites Watch
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Jonathan

2603 posts in 1647 days


605 days ago

Topic tags/keywords: mahogany ebony inlay ebony inlay epoxy inlay epoxy forstner bit rare earth magnet neodymium magnet countersunk

The area in-question is the left inlay.

I have a project that I want to finish up soon, and was almost done until I ran into a problem. I drilled 6-holes in the back of a piece of mahogany, then glued-in a neodymium magnet into each hole, slightly countersunk below the surface, around 1/16” or so. I say “or so” because I used a forstner bit in a handheld drill, and the wood is at an angle, so it was a little difficult to get everything exactly the same. Looking back, I should’ve taken the time to setup my drill press, but I was in the middle of something with it as well, so I decided to just use the handheld drill. At any rate, after the magnets were in and the glue was dry, I sanded down a little bit of an ebony pen blank, then mixed the ebony dust with epoxy to fill the holes. I filled all the holes slightly overflowing, then let it cure. I then took the project over to my Rigid oscillating sander and tried to slowly sand everything flush. Well, the magnet in the picture was apparently the high magnet of the group and I barely sanded through to the surface.

Now, this is the back of the piece, and it’ll rarely be seen anyway, but I am of the opinion that the entire project should be completed to the same level of quality, so I’d like to fix this. I’m wondering if it is safe to try and slightly drill out a little of the magnet? I don’t want to drill the whole thing out, just a small portion of it, then refill with the ebony/epoxy mix, and fix the mistake.

Are neodymium magnets OK to drill? I can’t think of any other way, other than trying to use some sort of paint or something to cover the magnet, but then this 1-inlay won’t match the other 5-inlays.

Any other suggestions will also be considered. I also thought about simply cutting a super-thin piece of mahogany as a veneer, then gluing it onto the back to just cover everything up and be done with it. Any thoughts? I’d like to keep the 6-inlays looking good, if possible, but at this point, I also just need to finish the project.

-- Jonathan, Denver, CO "Constructive criticism is welcome and valued as it gives me new perspectives and helps me to advance as a woodworker."


15 replies so far

View johnstoneb's profile

johnstoneb

616 posts in 769 days


#1 posted 605 days ago

It would be best to pop out the magnet and drill a little deeper and glue back in . Heat the magnet with a heat gun that should soften the epoxy and pry out the magnet.
Those magnet are very hard and probably won’t drill very easily.

-- Bruce, Boise, ID

View css's profile

css

3 posts in 605 days


#2 posted 605 days ago

I could be wrong but if it is what I think it is it is harder then a drill bit.

View Jonathan's profile

Jonathan

2603 posts in 1647 days


#3 posted 605 days ago

@Bruce,

Thanks for the response! I will try heating the epoxy with my heat gun after I’m off work and at home to give this a try. Hopefully that’ll soften it up enough to remove it. It’s Gorilla Glue Epoxy, as I had it left over from something else. I’ll just have to really be careful when re-drilling, as the wood is super-thin on this portion of the project. I’ll have to check the depth of the hole vs. the thickness of the wood now, since the forstner bit’s tip may end up poking through. If that’s the case, I think I’ll simply drop in a smaller magnet since they’re slightly thinner. Won’t have the same holding power, but it should still be fine.

@css,

You may be right. I wonder if I could sand the magnet down slightly to thin it out? Hopefully the above solution will work.

Thanks again for the quick responses.

-- Jonathan, Denver, CO "Constructive criticism is welcome and valued as it gives me new perspectives and helps me to advance as a woodworker."

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Jonathan

2603 posts in 1647 days


#4 posted 605 days ago

I’ll report back after I try heating the epoxy to see if it’ll soften enough to scoop everything out of the hole.

-- Jonathan, Denver, CO "Constructive criticism is welcome and valued as it gives me new perspectives and helps me to advance as a woodworker."

View SCOTSMAN's profile

SCOTSMAN

5241 posts in 2182 days


#5 posted 605 days ago

The truth is heat and magnets don’t go well the magnetism becomes lost with heat,so you would need to use plenty of coolant and a tungsten or diamond drill.I would redo the holes if I were you. Alistair

-- excuse my typing as I have a form of parkinsons disease

View DannyB's profile

DannyB

46 posts in 2018 days


#6 posted 604 days ago

The magnets should not be harder than the drill bit, if it’s a good HSS drill bit (or carbide bit)
Neodymium itself is not very hard, about 25-28 HRC, but neodymium magnets are neodymium-iron-boron. As a combination, they have a vickers hardness of between 550-650, which is ~53-57HRC.

A good HSS drill bit is at least 60 HRC.

So drilling them would be mighty painful, but should work. You’d be better off drilling them with diamond, and at that point, i would just make slightly larger holes as SCOTSMAN suggested.

Sanding them is going to be quite difficult, normally you’d grind them or something. Imagine trying to thin out a piece of HSS steel with sandpaper. It’s doable, but not something i’d want to do.

As for the heat issue, it’s actually a long and complex topic, but for neodymium, the short answer is it’s entirely possible to cause irreversible but recoverable (IE lost until remagnetized) loss in neodymium magnets using only a heat gun

View Mosquito's profile

Mosquito

4500 posts in 889 days


#7 posted 604 days ago

Also keep in mind that anything that you do happen to drill out, would likely stick to the magnet very strongly… and may be difficult to remove.

-- Mos - Twin Cities, MN -- Stanley #45 Evangelist - www.youtube.com/MosquitoMods

View Greg's profile

Greg

281 posts in 1470 days


#8 posted 604 days ago

Jon, I use a lot of these mags, and I was told NEVER to drill them! You can read the safety rules yourseld at magnets4less.com. These guys are the rare earth magnet gurus. I trust em, and like your ides for the mahogany veneer best. Good luck!

-- You don't have a custom made heirloom fly fishing Net? http://www.Sierra-Nets.com

View hhhopks's profile

hhhopks

559 posts in 974 days


#9 posted 604 days ago

Magnets should be hard and very britle.
As you try to drill them out it is more likely that it will crack.

Good luck.
I think you best bet is to heat it up so that you can remove the magnet.
They do sell donut shape magnets (used all the time in wooden toy trains) that you could epoxy back in place.

-- I'll be a woodworker when I grow up. HHHOPKS

View Howie's profile

Howie

2656 posts in 1519 days


#10 posted 604 days ago

Would it be possible to soak it in acetone, then let the acetone dry after removal? I thought that was what you used to remove gorilla glue.
I would be careful trying to heat these magnets, possibly they could explode( JMHO don’t know for sure)

-- Life is good.

View EEngineer's profile

EEngineer

885 posts in 2210 days


#11 posted 604 days ago

The truth is heat and magnets don’t go well the magnetism becomes lost with heat…

Ah, but the truth is that magnets don’t lose their magnetism until you hit the Curie Temperature. A quick look at Wikipedia shows that the lowest Curie temp for various magnetic materials is about 300-400 C. You aren’t going to get it that hot!

-- "Find out what you cannot do and then go do it!"

View HorizontalMike's profile

HorizontalMike

6914 posts in 1510 days


#12 posted 604 days ago

Just wondering here… Won’t these be hidden when in use? And if so, why not live with such a minor mistake? After all ALL of my pieces have mistakes and I know right where they all are, however others do not. They just admire the piece/project in its entirety. Just a suggestion.

-- HorizontalMike -- "Woodpeckers understand..."

View hg1027's profile

hg1027

26 posts in 699 days


#13 posted 604 days ago

Could you put a piece of veneer over the whole thing?

View DannyB's profile

DannyB

46 posts in 2018 days


#14 posted 604 days ago

@EEngineer

Actually, magnets don’t begin to permanently lose their magnetism until they hit at least the curie temperature.
The curie temperature is actually the point at which all magnetism is lost but it can still be remagnetized (IE irreversible but recoverable). Somewhere above that, you get permanent losses.

See http://www.magmamagnets.com/permanent-magnet-stability and such.

However, between the max operating temperature, and the curie temperature, you get irreversible but recoverable losses. That is, if you cool it back to room temperature, it will have lost some magnetism, but it could be remagnetized back to normal.

The max operating temperature of neodymium magnets depends on the grade (and it’s a curve rather than a single point), but even for the highest grade of neodymium magnets, the max op temp is only ~130 celsius. My heat gun can easily produce that temp.

View Jonathan's profile

Jonathan

2603 posts in 1647 days


#15 posted 599 days ago

Thanks for all the input on my dilemma. I have decided that I’m going to cut a thin mahogany veneer to go over the back. I may just leave it like that to completely hide the magnets, instead of trying to cut more holes in the veneer, then filling with more epoxy.

-- Jonathan, Denver, CO "Constructive criticism is welcome and valued as it gives me new perspectives and helps me to advance as a woodworker."

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