Rare Earth magnets

[Bill Wyko]

I own a Car Stereo shop and I have to replace my cards about every 90 days. Big woofers have big magnets which can in turn, cause big problems.

[Perry Holbrook]

Try, rare-earth-magnets.com That's where I buy mine. They have several sizes and list the strength of each size.

Perry

[Jim Becker]

Fred, the Shaker clock in my kitchen has two RE magnets employed as the 'catch' for the door to the key compartment. But in general, you only need the magnet on one side and an appropriate steel strike plate on the other side.

One piece of trivia...these are also what you want if you need to stick things to a "stainless" steel appliance. Regular fridg magnets don't work well in that job...

[Lee Schierer]

Two rare earth magnets are stronger than one rare earth magnet and a piece of metal. Magnetic strength varies inversely proportional to the square of the distance between them.

Magnetic media will be affected by magnetic fields. CD's are not affected, the data is stored in holes burned through the film. I can't say if DvDs are or not as I don't know how they are recorded onto the media.

Your TV picture (conventional electron tube type) will be affected by the close proximity of magnetic fields. If you magnetize the metal chassis you may have permanent color distortions unless you degauss your Tv.

[Rick Gibson]

Get them to close to a picture tube and you will get permanent color and picture distortion. They will magnetize the front of the screen which will pull the electron beam out of it's normal path. I have had to use an old bulk audio tape eraser to degauss my daughters tv more than once because the grandkids liked the colors made when they held a magnet near the screen.

[Doug Shepard]

That's a good point, and why I like the cups, because you can screw them into the wood. And the magnet WILL stay in the cup.

If you want screw holding ability you can also get what KJ Magnetics calls Mounting Magnets, with coutersunk holes directly in the mag.
https://www.kjmagnetics.com/products.asp?cat=110

Nothing against the cups. Just one more screwing option.

[Phil Thien]

Commercially pressed DVD's, as well as DVD-R/DVD+R and DVD-RW/DVD+RW disks are not magnetic, will not interact with magnetic fields, and should not be effected by magnets.

[CPeter James]

http://en.wikipedia.org/wiki/Neodymium_magnet

CPeter

[John Stevens]

Magnetic strength varies inversely proportional to the square of the distance between them.

It's been almost thirty years since my (only) college physics class, but I'm pretty sure that magnetism decreases proportionally to the sixth power of the distance between them. That is, if you double the distance, the strength of the magnetic field will only be 1/2^6, or 1/64th, as strong. For that reason, I doubt that magnetic door catches will have any effect on a TV, other electronic device, or magnetic storage media inside the entertainment center.

Moving along to stuff I actually know about: I have built five CD cabinets that have doors approx 60" tall by 8" wide. For a catch, each door uses one 3/8" rare earth magnet in a cup, with a metal disk located on the cabinet opposite the magnet (all from Lee Valley). They are not covered with anything but the little black membrane supplied with the kit. They don't look bad at all, and they keep the doors closed securely, but they don't make it too hard to get them open.

Fred, I'd suggest you mock one up and try it--I think it's the only way you'll know for sure whether it'll work for your application. Good luck!

[Rick Gibson]

For that reason, I doubt that magnetic door catches will have any effect on a TV, other electronic device, or magnetic storage media inside the entertainment center

John I have seen small unshielded speakers affect a computer monitor 6 inches away. Not knowing how close these will be it's something to consider.

On another note and I never thought earlier Fred these doors are held closed with one 3/8 rare earth magnet in a cup embedded in the center frame and a small metal plate on the door. As John said best would be to build a mockup and test it. Put the magnets where you plan to and check if there is no effect on the TV screen you are laughing. The rest of the electronic you would not have to worry about.

[Jim Becker]

Get them to close to a picture tube and you will get permanent color and picture distortion.

True...but there is no "picture tube" issue with Fred's setup. LCD...

[Rick Gibson]

True...but there is no "picture tube" issue with Fred's setup.

That would be called back to school and redo reading 101. Missed that in my first reading just saw TV. There will be no problem and magnets will work well. I use them to keep most of my cabinet doors closed and they work well.

[Karl Stewart]

If you want to hide them in the edges, I would use a slot cutter on the back of the door and insert; test with a tape cover.

I've done this through 1/8" hardwood, three 1/2" dia .10 thick RE mags will hold the weight of a 8" chefs knife and the holder on a fridge. http://www.sawmillcreek.org/showthread.php?t=49078 scroll all the way down.

Two facing each other [through the hardwood] should work well. If the test works, use epoxy to permanently mount. Most important: show pix when project is complete!

[Hank Knight]

Fred,

I built my daugher an easel with a paint box incorporated into the lower canvas tray. I used 3/8" rare earth magnets to keep the door of the paint box closed. My plan was to mortise the magnets into the door face and cover them with high pressure laminate so they would be invisible on the door face. I intended to use a corresponding metal disc mortised flush with the edge of the box that mated with the door. I used five magnets in a door approximately 20" wide. I was afriad that I'd used too many and that the door would be difficult to open. To my surprise, the magents were not strong enough to keep the door closed. The separation of the thickness of the high pressure laminate between the magnets and the oposing metal discs was enough to virtually destroy the effectiveness of the magnets for my purpose. I ended up replacing the metal discs with 3/8" magnets set into the little metal cups with opposing magnetic poles opposite each covered magnet in the door. This gave me enough attraction to accomplish my purpose, but I was amazed and disappointed at the effect the laminate had on decreasing the magentic force. I believe you would need actual metal-to-metal contact for 3/8" - or even 1/2" - magnets to work in your application. That's my experience, for what it's worth. For illustration, here's a photo of my finished paint box showing magnets in the cups set into the edge of the box. The opposing magnets are imbedded beneath the white laminate in the face of the open door.

[jeremy levine]

All you need to know ( almost)
http://www.leevalley.com/hardware/pa...77&cat=3,42363