Magnetics experts, please chime in...

This is not so much a request for your humble opinion as for your experience or theoretical expertise.

I’m posting this here mainly because it’s one of the three fora that I regularly read and I don’t think it quite fits in Cafe Society for its scant aspect of ‘creativity’. If a mod thinks it should be relocated, fine, but let me know where it goes so I can follow the responses.

I have a large collection of small martial arts weapons that are sitting in a big plastic box and I’ve always wanted to set up a display rack for them on a wall. I want to be able to reach over and grab a weapon, handle or use it, and put it back in place without diminishing the structure of the display – so I don’t want to just put up a dart board with all these things stuck in it. I’ve been thinking about framing a 2’ x 3’ section of corrugated sheet (like roofing material) because I think it would be novel, elegant, and relatively inexpensive. The key for me is that the ridge-and-valley pattern would make it easy to grab a weapon in the middle, do whatever with the weapon, then set it back to ‘rest’ on the ridges. I don’t have access to scrap corrugated roofing, so I’ll have to buy a fresh sheet and I don’t want to just experiment and waste money and materials on an idea that won’t really work.

That leads to my questions to you guys who are knowledgable about the physics/engineering of magnetic materials:

  1. If I zap a section of corrugated steel with a 12-volt battery, would the surface/ridges attract my steel blades and chains, or would only the edges of the sheet be attracting and holding things?
  2. If I connect a 9-volt battery to leads attached to opposite edges of a corrugated steel sheet and leave it connected, would it hold any better than the 12-volt zap?


Neither of your ideas will work.
At all.
Trust me.

Go to the hobby store and get a sheet of magnetic flippy floppy. Glue small squares of the stuff to the corugated metal, stick weapons to the magnets. Alternatively, go to the hardware store and buy some rebar and a couple big spools of insulated 14 ga single strand wire. Wrap it around the rebar, mount the bars behind the corugated metal & electrify your electromagnet (not sure if you can plug this into the wall, wear gloves when you plug it in?).

Would a magnetic knife holder work?

And, as a bonus, have the potential to produce spectacularly bad outcomes for you and/or your stuff.

It’s not a display approach I would use at all, because even at its best, it’s not secure, and falling weapons are bad. If you insist on it, however, you should use permanent magnets, rather than trying to do anything with electromagnets.

Better still, use hooks, brackets, straps, and the like to make secure supports for the weapons.

Sensible & safe, but I think the look the OP was going for was more of a “magic” no-hooks thing. Thus the favor for the stickiness of magnets.

Yeah, hooks.

You need neodymium magnets. I built a wooden knife rack along the lines of this using the magnets from discarded hard disks. I’d recommend buying the magnets instead - I had to chisel out the back to fit the oddly-shaped HDD magnets.

You’ll need to experiment with different sizes and arrangements of magnets to hold things firmly.

Then at the very least, there should be a catch-tray or something below the rack to keep stuff from falling all the way down. Tabi don’t fit well without toes, you know.

Fair enough, and I suspect that’s largely why I can’t already buy something through a martial arts catalog of some kind. However, I posted to this forum to get more of the specifics on why they won’t work and open up something of a discussion from which to brainstorm ideas.

I have seen the magnetic tool-holders and knife-holders. My collection is large and assorted enough that several would be needed and my preference is for a ‘two-dimensional’ display/rack rather than the linear presentation that a long tool-holder bar would provide. At this point I think lining up six or eight of those magnetic bars would look more crude (and at >$5 per bar foot more expensive) than what I have in mind. However, it may end up being my only choice.

I’ve toyed with an idea similar to Sun-Jester’s; magnetizing several rods and setting them up in a parallel configuration maybe an inch away from a surface. Then I’d lay the weapons across various rods and my fingers would be able to get between the gaps for grasping them.

I’m really thinking electro-magnets are a bad idea because eventually a battery will fade out and drop everything. I don’t want to be attaching extra stuff (magnets, velcro, straps, whatever) to the weapons themselves, though, because that will reduce the grab-and-use impression I’m trying to convey with this display. Otherwise I know I’d be able to skip magnetizing the display or could just press everything behind a covering sheet of glass or plastic. Oh, here’s a thought: Think of [COLOR=Green]Crouching Tiger/Hidden Dragon and that rack of available weapons in the studio/school in owned by Yu Shu-Lien (Michelle Yeoh). I want to be able to grab-and-go that quickly with my small weapons (and my wife says she wants to make symmetrical display patterns that will change and stay symmetrical as the collection grows).[/COLOR]

Keep the ideas coming! They are welcome and they’re helping me brainstorm.


Yes, there will already be a tray.
Plus, I don’t have small kids who will eat hooks or magnets (or weapons).



As others have said, neodymium magnets are the way to go.

Personally, what I’d do is get a sheet of wood of the appropriate size, and on one side drill wide cylinders about halfway down (say, 1/4"). Put them in a grid fashion with a spacing appropriate to the number of weapons you have. Get a bunch of disk magnets and glue them in place. On the other side, apply a piece of felt, and frame the whole thing. The felt will provide enough friction to keep the pieces in place as long as the magnets are strong enough.

The main problem is that the magnets won’t be cheap. But there’s no way around that, unless you can find them scrap. I would go with something like this. They’re only a few bucks each, but you’ll likely need a few dozen.

Nice rack for kitchen knives. Your project?
Was there a calculation involved in the intended spacing, or was that “Well, an inch apart seems reasonable enough.”?


That’s not mine, no. Mine’s just one piece of wood with two old HDD magnets.

I experimented with the magnets behind pieces of cardboard and thin plywood to get an idea of the depth (2mm between the magnet and knife is good). There wasn’t any spacing to determine since I’m only using one magnet per knife.

You’re not going to be able to magnetize something yourself, not if you want to hold anything bigger than a paperclip. Buy a sample assortment of neodymium magnets on Ebay so you can try out different sizes and strengths.


So, what about a sheet of that magnetic sign material, backed by a sheet of corrugated roofing material? Plastic seems light and would support the shape, while the sign material would (?) hold the weapons. I was originally thinking of doing it with a metal backing and jumped to thinking I could just skip the sign material in favor of magnetizing and using the corrugated sheet itself. However, as Tellyworth has noted, a backyard attempt at magnetizing something that big won’t hold much of a weapon. I have used paperclips as weapons before, but a frame full of paperclips on the wall doesn’t seem like an interesting idea to me and doesn’t help me display the rest of my arsenal at all.


Get some rare earth magnets from Harbor Freight. Cheap and strong.