Attaching things with magnets?

[Andy Dingley]

I need to attach a couple of nameplates to a diesel loco. It's not mine and they're only on there for one day, limited to 25mph.

So my thought was magnets. Any suggestions?

The nameplates are 4-5 foot long and wooden. Inside them is a recess 80mm wide and 18mm deep. So far I have a bunch of two dozen 30x8x3mm rectangular rare earths.

My plan is to use the magnets in pairs, stuck to a 3" square of thin steel sheet, screwed inside the wood. This is screwed through foam washers and bent so that the magnets can just touch the surface. Three steel mounts to a nameplate.

Ho do I attach the magnets to the steel sheet? I want them to stay in place when removing from the loco, so ideally something a little stronger than magnetism alone. Epoxy? Does this work on plated magnets?

I need to avoid scratching the loco (as best I can). Insulation tape over the magnets? Brown parcel tape? Or nothing?

I'm thinking about shipping these plates with a couple of loops of strong ribbon as "pull off handles".

As usual, I have no time t make this stuff, then have to send it to the loco owner and hope it all works on the day. No chance to test beforehand (I'm testing it on the fridge).

I'm assured the loco is not aluminium sufficiently well that it's Not My Problem if it is.

Thanks

[The Natural Philosopher]

Yes, epoxy works, as does car body filler and even contact adhesive.

Id use carbody filler because it doesn't suffer from inadequate mixing as epoxcy can

Nothing. Just be careful. Use a bit of clingfilm to get all in place, them lift one side and remove and then repesat for other side.

[alan_m]

In my experience the plating on Ebay rare earth magnets peels off if you sneeze!

I have some magnets with holes through the middle and can be attached with screws

Is the surface you are going to attach to perfectly flat. If not flat, not all of the magnets will make contact or hold.

[Tim Watts]

You can buy magnets with countersunk fixing holes in the middle :)

[newshound]

That's what I would use. Covered with a single layer of PVC electrical tape they will stick well to an iron or steel surface as long as they can align. But if it is painted with a reasonably durable finish, then chrome plated magnets should not scratch it especially if pulled off carefully without sliding.

[Peter Parry]

Old hard disk drives have one or two flat magnets of very impressive strength. Some come with mounting holes, other can be epoxied in place.

[Thomas Prufer]

Epoxy does work on plated magnets. The plating may peel, but eventually, not in one day. Beware that the magnets may move towards or apart from each other when the epoxy is setting if they are close together. (Nothing more annoying than to ge them just so, and snap, they jump and kiss each other in a mess of half-set epoxy...)

Failure mode would probably be the steel sheet peeling off the magnet. Can't see that happening in one day, at 25 mph. (Hard disk magnets are epoxied to their mounts/pole pieces, and can be removed by bending these. The magnet stays unbent, the pole piece peels away from it -- this requires mole grips, as the pole pieces are ~2mm. The plating usually, but not always, stays intact.)

Well, nothing, as you won't be the one scratching the locomotive by sliding the magnets around rather than pulling it off. And the "pull off handles" are a very good idea, as the signs can then indeed be pulled off without sliding.

(If you must: the thinnest tape you can get away with, as the holding force drops rapidly with separation. I'd leave it off -- it's locomotive with paint, not French polish.)

Thomas Prufer

[Chris J Dixon]

Whatever you do, won't you have to convince whoever is signing the "Fitness to run" documents that it will be adequate?

Chris

[Brian Gaff]

What you need is that stuff the advertisers use for this sort of thing. Its a kind of sheet orf bendy plastic which carries magnets over the whole surfagce which means that no one area is going to scratch paintwork. you then just glue the front of the sign to the sheet.

Brian

[Nightjar]

On 08-Jun-16 8:25 PM, Andy Dingley wrote: ...

Nothing, if you want maximum grip. I used to make a medical device that used a magnet to hold the working part in place. It used extremely strong, purpose made, magnets, which are very difficult to lift straight off a steel surface. I still have a number of those and, if I want to make them much easier to remove, I just put a bit of electrical tape over the face.

[Andy Dingley]

It's not main line, so there's no onerous paperwork.

[spuorgelgoog]

Still subject to safety verification or safety management system change management procedure.

A nameplate flying off at 25 mph will still attract the attention of RAIB, especially if it hits someone, and you don't have the paperwork to back everything up.

The main problem with anything magnetic is if the wind gets under an edge. Magnetic vinyl on flat steel car panels is usually ok up to 40 mph.

Owain