Tell me about Mgnets!

[Homerjh]

Righty, tried to search on here but to be fair, the search is a bit pants so difficult to drill down.

Interested in testing a few ideas that involve magnets, but no idea where or what to look at. Initial requirements are fridge magnets and also larger ones for the 'bottle opener' projects that are online to stick to a fridge and suchlike.

the best seem to be the 'rare earth' (RE from now on!) type, smaller, easier to integrate into items and also stronger.

A google shows normal fridge magnets, but in my experience they are always weak, anything more than a sheet of paper and they can fall off, and whilst the RE cost a lot more they have stronger hold, which is the point.

so any suggestions as to where to get them and also suggestions on size? i have tested one that is 8mm x 4mm (i think, so 8mm long) and that has quite a strong hold so seems to be a good solution for fridge magnets.

however for the beer opener projects they say larger, so 1/2" or even 1", so will be a trial and error, this is to stick it to the fridge and also catch the caps.

so how to stick? is hot glue suitable or need epoxy?

any need for ones that have a screw hole?

anyone also had issue putting a thin cover over just to cover the magnet (so get a plug and glue it in and trim off, probably 1mm or so).

thanks

 

[MattRoberts]

Yeah, neodymium magnets offer great strength to size ratio. You can get them easily on eBay or Amazon. They often show their weight capacity in kg.

You can attach them with epoxy, or if you get countersunk ones you can screw them in to something.

If you're looking to make a bottle opener that stays stuck to the fridge while opening, you'll need to use a few magnets.

Not tried plugging them - anything you put over it will probably reduce the effectiveness - and why plug it if it's not going to be seen anyway?

 

[Homerjh]

thanks, and yes, that was a thought that no need to plug as they are on the rear, but not sure if it would make the overall item look 'nicer'.

thanks

 

[Aggrajag]

Bear in mind the neodymium magnets are very brittle, for example if you let two simply collide together under their own forces there's a good chance one of them will shatter - I had some that did exactly that.

 

[Sheffield Tony]

I made a serving hatch (frame + doors) for FIL. To hold the doors shut, I fasioned a "catch" from a pair of small R.E. magnets, meeting North to South poles. One magnet of the pair was burried in a block that served as the stop for both doors, attached to the top of the frame. Recessed in from the surface that isn't exposed when fitted, with probably less than 1mm of wood over the acting surface*. The other was pressed into a small hole drilled in the back of the door. The magnet was just the right size to fit beneath one of those self adhesive bump stops used on kitchen cabinets. There was enough force to keep the doors closed, just. Looks nice though, IMHO.

* Edited to add - I did that by chiseling the hole, epoxy the magnets in, plane down cautiously to just under a mm of wood left covering the magnet.

 

[monkeybiter]

IME the useful force disappears rapidly with distance, so trial and error may be needed if plugs/covers are used.

I've successfully used CA glue to fix them in a hole, they're usually useful sizes that correspond with drills to make a snug fit [if round].

These might be of use to see what's available, may easily be cheaper elsewhere..

http://www.magnetexpert.co.uk/Online-Shop/Neodymium-Magnets.htm

http://www.first4magnets.com/neodym...TLHGcgZiuC-1g4a6uoaJyXZZV_j2vNZabfRoCrlrw_wcB

 

[ED65]

so any suggestions as to where to get them and also suggestions on size?

I think buying from one of the Chinese suppliers is the way to go. The magnets are all coming from China originally anyway, so why pay the middle man and the retailer's overheads and profit margins?!

An advantage of getting them pretty cheap is you can splurge and buy a bundle of different sizes to try them out, rather than doing your best to firm up on what you think you might need before paying full retail.

so how to stick? is hot glue suitable or need epoxy?

Hot glue can work very well but epoxy would give you a more secure hold.

If the magnet will end up buried in the wood though you can just use your woodworking adhesive, the glue only has to hold the magnet in place and stop it rattling, not hold on to it for dear life and prevent it being pulled free.

 

[ColeyS1]

You can get them with holes already in the middle to suit a countersunk screw

Coley
Oops my bad. Looks like that type might not be suitable

 

[Rhyolith]

This is a good site for magnets: http://e-magnetsuk.com

 

[custard]

Bear in mind the neodymium magnets are very brittle, for example if you let two simply collide together under their own forces there's a good chance one of them will shatter - I had some that did exactly that.

+1

If you use the magnets with a countersunk screw hole through them you need to nip them up until they just stop rotating, any more and they shatter.

 

[Eric The Viking]

Don't forget: if you take a pair of rare earth magnets and attach them to a steel backer ( N-steel-S ), the resulting "horseshoe" magnet will be more than twice as strong as one on its own. I did this recently as I needed a strong magnet to hold a trap door open on a scaffold tower: Steel plate on the trap door, pair of 20mm disc magnets on a steel plate on the framework. It works a treat. I stuck the magnets to the steel using a smear of high-strength epoxy, then screwed the steel plate to the aluminium frame, having first-of-all drilled it for self-tapping screws.

I can't imagine hot-melt glue would be strong enough against the magnetism, but I'd be interested to know how it's done, if it is.

 

[ED65]

I can't imagine hot-melt glue would be strong enough against the magnetism, but I'd be interested to know how it's done, if it is.

Often when magnets are being held by hot-melt glue they're at the bottom of a hole, with the pulling force going into the glue not out of the hole.