Rare earth magnets

3 toed sloth · #1 20th Dec 2011, 01:23 PM

Finishing off a cabinet which has two doors closing and meeting in the middle. I'm thinking about using r/e magnets for catches, can anyone who has used them give me some advice?

The top overhangs the doors, so I could place something in the top of the door and the underside of the top. Or one in the back of the door and one in the front edge of the bottom shelf, which the door stops against when it closes.

Do you put magnet to magnet, or magnet to metal?

Would one at top only be enough or do I need top and bottom?

There are different sizes, and so I suppose, different strengths. I vaguely remember seeing a mixed pack available somewhere so you could gauge the different sizes and strengths, does anyone know where these are available?

Answers to any or all of these questions would be much appreciated.

Thanks,
Peter S.

Skew ChiDAMN!! · #2 20th Dec 2011, 01:56 PM

I'd be inclined to buy a pack and see how they go against a small piece of metal. Avoid trying magnet-to-magnet, until you know how strong they are as rare earth magnets are strong and it can be a right PITA trying to separate them afterwards!

Similarly, it's better to put a magnet/metal pair near the top of the door and - if that isn't strong enough - to put a second magnet/metal pair near the bottom instead of just putting a magnet/magnet pair near the top.

Why? Well... the 2nd magnet/metal pair will give you the same latching strength as one magnet-to-magnet, but without the strain on the glue holding the magnets into the timber.

It can be damned frustrating to fit a magnet-magnet latch, test the door... discover it's a bit more tightly latched than you thought, so give it a jerk and promptly discover that one magnet has pulled free and is still stuck to the other. DAMHIKT.

3 toed sloth · #3 20th Dec 2011, 02:40 PM

Thanks Skew,

What you're saying makes a lot of sense. I suppose each situation is different so trial and error seems the way to go.......well, hopefully more trial than error.

These things could be more trouble than they're worth, still I'd like to give them a try. I'll have to start small & magnet to metal and go from there. Might even be worth making up a kind of test rig with a bit of MDF just to get a feel for it. Once I start drilling in the real thing I'm too committed if I decide I don't like it.

rustynail · #4 20th Dec 2011, 06:51 PM

Depending on the thickness and size of the doors positioning of catches can be very important for long term use. Thin framed doors have quite a lot of flex when held at either the top or bottom. Where possible, it is a good idea to place catches close to handles as this helps to eliminate door flex when opening. R E magnets are available at Jaycar Electronics Penrith.

3 toed sloth · #5 20th Dec 2011, 08:22 PM

Hi Rusty,

I agree with you, but there is no way to put the catches near the handles in this case. The doors are fairly rigid in this piece, they are 500mm x 250mm Jarrah frames at 18mm thick and M & T joints.

Even so I am concerned about the flex effect over time. I am thinking maybe a catch top and bottom for balance and/or the minimum strength magnets possible to do the job. The doors only have to stay neatly closed so I suppose they don't need a huge amount of magnet power.

issatree · #6 20th Dec 2011, 08:33 PM

Hi Peter,
Yes, What has been said, as I would also put the Magnet, where ever the Knob / Handle is.
You can also get the Magnets from John McJing. His Add is right on this Page.
I bought a couple that would be 5/8" 16mm.
I think, & you may only need a bit of Tin or whatever,
You would need to bore a hole to place the Magnet in.
I also found that Loctite 401 will not do the job, so you may need to Use a 2 Part Epoxy.
I don't think Magnet to Magnet would be a good idea, as these Magnets are, as they said, very strong.

T.C · #7 20th Dec 2011, 09:38 PM

I've been looking at buying some magnets for a project of mine and found they are tons of them on eBay. Can't remember which seller had them but you can definitely buy sample packs, some also give them a hold strength rating.
I also found this mob in Melbourne Specials - Sample Packs - Aussie Magnets
They were a bit far from my place but I eventually found and bought what I needed from this place Fastmag Magnets, Rare Earth or Meodymium, Ferrite and Magnetic Sheeting after playing around with a few different ones, I don't think they had sample packs though.

MajorPanic · #8 20th Dec 2011, 10:54 PM

You should learn a little about REM's

I buy mine from this guy Frenergy Magnets items - Get great deals on Diameter 1mm - 20mm, Length 1mm - 20mm items on eBay Stores!
He's Brisbane based & has a lot of excellent info on magnets.
The N52's are REALLY strong.
Have used 2 to hold large cabinet doors closed. One in the top of the door & one in the cabinet, works just like self-closing doors

Magnetic Strength and Gauss: Magnetic strength and Gauss ratings can be confusing. Many companies advertise their magnets and magnetic products with the “internal gauss” rating which is very different from the actual “surface gauss”. The surface gauss is dependent on the N-rating, size and shape of magnet. We provide a magnetic force calculator to calculate holding force and gauss at our website. Just type “Frenergy” or “Magnetic Force Calculator” into a search engine like Google and find our website. We have provided the surface Gauss in the item description above and also further technical information in the tables below.

AlexS · #9 21st Dec 2011, 08:57 AM

I've used a pair of 6x6mm neodymium REMs on cupboard doors to hold them closed. They are magnet to magnet, and are strong enough to hold the doors closed but not to pull them closed.
Just make sure you get the polarity right.

3 toed sloth · #10 21st Dec 2011, 06:12 PM

Thanks for all the replies.

Issatree, good point about the glue, don't want the magnet so strong it pulls straight out of the woodwork. Looked at McJing, no sample packs but a few different shapes including squares, and discs with a countersunk hole in the centre.

T.C. Thanks for the info. Aussie magnets have the ideal sample packs for what I want, 32 small magnets for $12 or 16 bigger ones (still small) for $20.00. I am going to order the $12 pack as they come in sets of four and if I go top and bottom on each door that kit may be all I need.

Major Panic, yes there's a bit more to these magnets than meets the eye. The gauss rating may be useful for technical fields, but it is a bit full on for me. The Aussie Magnets site uses a rating called "pull strength". All their magnets are given a pull strength rating in grams or KGs and means the amount of weight required to pull the magnet off a piece of 3mm steel plate.

Had a look at the Frenergy site and WOW do they have some magnets. May well return to that site once I sort out what magnets I am going to use generally. Lots of different shapes to choose from. Did have some sample packs but too big and varied for what I need.

Alex, that is what I want to do. The sample pack I'm going to buy doesn't have 6mm x 6mm, but it does have 6 x 3 and 8 x 5mm and some even smaller. The great thing about these magnets being so strong is that you can use one quite small and so not too visually obtrusive.

Can you explain where you put them specifically on your cabinet?

AlexS · #11 21st Dec 2011, 08:41 PM

I put them level with the handle. On one cabinet that's near the middle of an 1800 high x 320 framed glass door, on the kitchen cabinet it's near the top.
I get them from Maglab.

Clinton1 · #12 21st Dec 2011, 09:43 PM

The magnet and metal do not need to touch. If you can set the magnet away from the metal then you reduce the 'pull'. Handy if you have space within the frame. About 1/2 the distance between magnet and metal = double the pull, and visa versa.

3 toed sloth · #13 22nd Dec 2011, 08:58 AM

Thanks Alex, the Maglab site looks good, and the only one I've seen that thought to put a scale against the picture so you can see how big they are.

I can't put my magnets near the handles as the handles will be mid height between top and bottom and magnets have to be either top or bottom or both. My doors are only small at 500 x 250 so I'll have to see if I can get away with one top or bottom or top & bottom.

If I go top & bottom I'll have to be careful not to create too much pull as the cabinet is a bit top heavy and I don't want to be pulling the whole thing over, trying to open the door.

Clinton, I'd wondered about that. By adjusting the depth I could calibrate the strength of the pull. Difficult to test, though, as magnet has to be glued in place to test. I am thinking about making an MDF box with a door for testing. The magnet could be glued into a removable insert. I could then move the insert around to try different depths, or fit different inserts with different size magnets and combinations.

A lot of work, but I will need to test my setup somehow before I permanently install.

rusel · #14 22nd Dec 2011, 10:01 AM

Hi
I am in the blue mountain myself and I have some rear earth magnet here if you want to come and have a play, might help you decide which way to go.
I will pm my phone number Call if you wish to come around.

Russell

Clinton1 · #15 22nd Dec 2011, 10:15 AM

Quote:

A lot of work but...

Thats what you get for trying something new.