odd question re: magnet resource

[Stephanie B]

The “strength” Of magnets is usually measured as a force that’s pulling perpendicular to the plane of the mating surfaces. If you’re hanging something on the ceiling you could use a “40lb” magnet to hold 40 pounds. If you’re hanging on the wall you would need a coefficient of friction.

Good to know for those who want to use a magnet to hold a gun under something.

[rob_s]

We use strong magnets in our work and have done business with K&J Magnetics for over 15 years.
They are good at answering application questions. When they say "be careful" they really mean it, but if you choose the proper power in the proper size, with the proper attachment method, it's really nice.

I've reached out to them, but that's also the vendor where I currently have about 10 of each size for a range of strengths in my shopping cart.

IIRC from a book I found on speakers, wood has essentially no magnetic shielding properties.

I seem to be hearing similar. I think I'll wind up having to test.

The “strength” Of magnets is usually measured as a force that’s pulling perpendicular to the plane of the mating surfaces. If you’re hanging something on the ceiling you could use a “40lb” magnet to hold 40 pounds. If you’re hanging on the wall you would need a coefficient of friction.

My wife was telling me that a lot of cruise fanatics buy magnets to hang things in their staterooms, and they all complain that their 2 lbs shirt pulls a "10 lbs" magnet down the wall. I thought it was funny that what you describe above hadn't occurred to any of them![/quote]

https://www.kjmagnetics.com/calculator.asp

I'll have to try monkeying with that. Thanks!

[Crawls]

I am always amazed how much stuff is out on Amazon:
https://www.amazon.com/s?k=magnets&ref=nb_sb_noss_1

Maybe a little better performance information on McMaster:
https://www.mcmaster.com/standard-magnets

Those Easy On/Off rare earth magnets from McMaster as cool. I've used magnetic lifting devices for cranes and overhead hoists that use similar magnets and I'm always amazed by how well they work.

In addition to txdpd's excellent comment about the magnetic force being normal and needing to take the surface coefficient of friction into account when sticking stuff to a wall, here are a couple more useful tidbits:
First, the magnetic force is inversely proportional to the square of the distance, so small changes in the distance a magnetic field is working across have big impacts on its strength. For example, If a magnet is rated at 100lbs at say 1mm then you double that distance to 2mm, the magnetic strength is reduced to 25lbs. I've dealt with some thick painted surfaces where that came into play. If you're working through 1/4" to 1/2" of wood, it will obviously play a big role.
Second thing watch out for are moment forces rather than pure tension forces. If there is a moment force (imagine prying the magnet away from a steel surface) the forces aren't evenly distributed across the face of the magnet and the magnetic bond can fail pretty easily. That also explains why it's pretty easy to wrench a pistol off one those magnetic pistol mounts that are rated for 40 or 50lbs.

[RoyGBiv]

At the end of your research, are you looking for one or a handful or thousands of magnets?

I do some business with several (China based) magnet factories that might (depends on what materials/technology/strength/shape/etc) be able/willing to respond to a clear specification, assuming they had a chance at some volume business at the end of the process.

I'm not the technical expert, I handle the business end of things.

KJ is a good resource if you're looking for onesie-twosies.

[rob_s]

At the end of your research, are you looking for one or a handful or thousands of magnets?

I do some business with several (China based) magnet factories that might (depends on what materials/technology/strength/shape/etc) be able/willing to respond to a clear specification, assuming they had a chance at some volume business at the end of the process.

I'm not the technical expert, I handle the business end of things.

KJ is a good resource if you're looking for onesie-twosies.

no just a handful.

[rob_s]

Unfortunately the shipping is killing me. I guess I should just get 5 or so of each since it's the shipping cost that's eating me and I'll figure out a use for the leftovers some kinda way...

[RoyGBiv]

^^ how much for USPS?

[rob_s]

^^ how much for USPS?

good catch. I missed that button. Much more palatable.

[txdpd]

Good to know for those who want to use a magnet to hold a gun under something.

Or if you have a stack of magnets that are too strong to pull apart, you can hold them on the edge of a table, with one over the ledge and tap them off one at a time with an aluminum hammer (or any non-iron hammer). Or just slide them apart.

Cut up plastic milk jug make nice sliders to put between magnets to get them in position.

[JTMcC]

I've reached out to them, but that's also the vendor where I currently have about 10 of each size for a range of strengths in my shopping cart.


I seem to be hearing similar. I think I'll wind up having to test.


My wife was telling me that a lot of cruise fanatics buy magnets to hang things in their staterooms, and they all complain that their 2 lbs shirt pulls a "10 lbs" magnet down the wall. I thought it was funny that what you describe above hadn't occurred to any of them!

I'll have to try monkeying with that. Thanks![/QUOTE]

Just remember that they sell small magnets that can be almost impossible to remove from steel without large leverage tools and significant effort.
Buying a range of sizes is really the best way to hone in on what you really need for different applications.
Most people I think are unaware of how powerful a magnet you can buy.
But they really make our work day easier.