Sticky front door with strong magnets

[john brook]

Have some shed doors (identical to a normal solid wood front door) that i want to simply remain closed by the use of magnets, when coming in and out a lot.

The neatest way i can think of is using some of those strong magnets with holes already in them screwed to the inside door frame at the top and with a small length of wood screwed to the top inside face of the door raising another magnet that meets up with the one on the top frame. Hope that's clear.

I have tried those double quite strong cupboard magnets, the kind you can get in B and Q type stores and i thought that they would hold, surprisingly even a small wind just blows the door open.

I can buy the Neodymium (strong type) magnets with holes with a; 1.6, 2.4,

4.8, 5.6, or 9.8 kg pull strength. Any ideas on what strength you think I should go for? Bearing in mind we dont want the door too sticky.

[The Natural Philosopher]

Id go for size rather than flux density.

Try a pair of buggered loudspeakers - the ferrite mags in those and the iron parts that go with them should be nearly all you need.

You can back off the stickiness by adding a layer between the mating surfaces..bit of fablon etc, to fine tune it

[dennis]

Not surprising really, even a small pressure difference on a surface the size of a door results in a large force. One psi will result in a force of about 65 kg per sq foot. The magnets used to hold security doors shut apply about 400 kg force so that gives you the upper limit. The size of the smallest person will give you the lower limit. Then fit a bolt and/or a door closer.

[Andy Dingley]

Definitely. Nd are far "harsh" is used bare, and they're too small to use at a distance. If you did use them, I'd be inclined to add iron poles, just to spread the flux.

Agreed. Plenty strong enough and usually a better size.

Why a pair though? One and a good polepiece. I've got a couple of magnetic door catches like this, either speaker magnets or microwave oven magnetrons, covered with a layer of sticky neoprene foam as a cushion.

[Tabby]

Forget it, seasonal movement and vibration will make this work badly unless you use excessive magnetic forces. Go instead for a roller catch, which will keep it closed with the same force regardless of these factors.

NT

[RobertL]

I'd buy the biggest. you an always mount them slightly offset to reduce the pull.

Robert

[The Medway Handyman]

Fit a door closer. It will shut the door for you & hold it closed - you can adjust the force. You can pick them up for a £10

[Alan]

In message , john brook wrote

If you have an old computer hard disk take it apart and get the magnets

[Tabby]

unmitigated pita when you're going through frequently. Avoid.

NT

[dennis]

Most door closers are adjustable, RTFM.

[Andy Dingley]

Only the top mounted ones. The cheapies that mount in the middle of the hinge side are pure springs, no dampers, so they don't slow closing at all.

[Tim Watts]

The hinges I've seen had a further advantage of being adjustable but taking a peg out, torquing it up and reinserting peg.

The lack of dampers can be a problem though - lots of door banging unless you set the thing on the weak side.

[The Medway Handyman]

Didn't anyone follow the piggin link?

[andrew]

I've had these cheap ones fail in less than a year from frequent use, the spring gradually chafes it's way through the pot metal like housing.

AJH

[root]

I used a couple to hold the kitchen door _open_ Briefly: one magnet on the body of the door handle, another on into a wooden stop attached to the wall. Cut a piece of plastic eraser and attach to the wooden stop above or below the magnet. Adjust the depth of the eraser so that the magnets don't quite touch.

The only hard bit was finding an adhesive to hold the magnets in place. Epoxy doesn't last - too brittle. Stixall is the current goop of choice. It has a certain amount of natural flexibility and sticks well to the ceramic magnets, the aluminium door handle and the wooden stop.

[Andy Dingley]

Yes, those top-mount Ryobi things are rubbish (see other post about wanting Toolstation to sell better quality parts). I put four of them in Dad's place, they all failed within a year. The damper mechanism was OK but the joints in the arms were so badly made. The common fault was the riveted pin working loose in the arm, which I guess I could fix by welding.

The two that were really needed, I replaced with centre-mounted simple spring closers.

re this thread, they were at least adjustable for closing speed.

[Andy Dingley]

I use polyurethane panel sealer (like silicone, but extra sticky). The stuff only lasts a month once the tube is opened, so if I've had to buy one (usually waterproofing vehicle or boat panels) it gets used for everything afterwards. It works well as an extra-flexible glue, so long as you don't mind a thick fillet.

[root]

I also tried PU (Gorilla glue), but that had the same drawbacks as epoxy. There does seem to be a benefit in having a slight flexibility in the adhesive.

[Jethro]