magnetic knife rack question

[ed kerns]

As projects go, this couldn't get much simpler. I plan to take a board, maybe 1 X 2.5X 18", embed some rare earth magnets in the back side and hang it on the wall as a knife holder. I'm thinking I'll use a forstner bit to drill out the back side within about 1/8" of the front surface. I'll size the holes to whatever magnet diameter I choose and then I'll cover the back with matching wood. My question is, without building a prototype, I have no idea how many magnets, and what size, depth, hole pattern etc. would best serve my purpose. I'd like it to hold everything from a paring knife to a cleaver - securely, but not so securely as to require two hands to pull the knife from the board. Any advice appreciated!

[Lynden]

A line of bar magnets might work better than individual round magnets.

https://www.amazon.com/s/ref=nb_sb_ss_i_...HEG6RHL1JZ

81+kyRqK7DL._SL1500_.jpg

A channel magnet is stronger than a bare bar magnet.

https://www.amazon.com/s/?ie=UTF8&keywor...5eks_e_p37

"Magnets do their best work when focused. The natural field of a magnet is polar radiating loops.
Magnets have equal fields. The trick is to get both fields working for you.

A ferromagnetic backing plate placed against one side of the magnet creates a more efficient path for the flux lines to follow. It also creates a radiating pattern favoring one pole, which effectively points the majority of the magnetic energy in one direction.

When a magnet is placed in a ferromagnetic cup, the cup further magnifies the effect by eliminating the air gap (air is a poor conductor of magnetic fields) and brings both poles of the magnet to grip on the same surface. This is similar in principle to a horseshoe magnet. A rare-earth magnet in a steel cup provides four times the strength of a bare magnet. A cup provides a disc magnet the optimal magnetic flux focus into the smallest gap area." quote from Lee Valley Tools

[daddo]

Won't work with stainless steel blades.

[Cooler]

I saw an interesting design where the they cut a slot at the very rear of a butcher block counter top and slipped the knives behind the drawers.  It took up no space.  But would be tough to do with granite, marble or quartz.

With Formica a nicely formed wood opening would be needed.  

Sorry, no magnets involved.

[Bob10]

As projects go, this couldn't get much simpler. I plan to take a board, maybe 1 X 2.5X 18", embed some rare earth magnets in the back side and hang it on the wall as a knife holder. I'm thinking I'll use a forstner bit to drill out the back side within about 1/8" of the front surface. I'll size the holes to whatever magnet diameter I choose and then I'll cover the back with matching wood. My question is, without building a prototype, I have no idea how many magnets, and what size, depth, hole pattern etc. would best serve my purpose. I'd like it to hold everything from a paring knife to a cleaver - securely, but not so securely as to require two hands to pull the knife from the board. Any advice appreciated!

Not the question you asked but might be the answer you need.  It might be cheaper to buy a knife rack and pull the magnet instead of just buying magnets plus you know it will work for what you need.  If you have a second hand store near you probably even less.  I was trying to buy magnets by the 100 on ebay.  Price was close to buying finished products so I am still looking

[Lynden]

More from Lee Valley Tools....

Knife Holder

I have always found it jarring to put a sharp knife on an ordinary magnetic knife holder. The blade is held against two steel strips. It is not really a question if this will cause dulling, just when it will happen.

Regardless of how careful you are, sooner or later the sharp edge will hit a bar. On the other hand, wooden knife blocks clutter up a counter, even though they are kinder to knives.

There is a third choice. You can make a wooden knife holder using rare-earth magnets. The magnets are strong enough that you can put a layer of wood between them and the knifes. The knives are held securely in place, but never get damaged because they only ever come in contact with wood, not steel nor the magnet. The simplest way to do this is to drill 1/2” holes to within 1/16” or so of the face of your wooden bar. Whether you use a brad-point drill or a forstner bit, the center brad will probably put a hole in the face of the bar. You can put filler in this if you wish, but the whole job looks more professional if you drill it out to 1/4” or 3/8” and put a wooden plug in it. The job looks neater and the plugs mark exactly where the magnets are in the wooden bar. This makes a far better knife rack than you can buy in any store. 

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[MichaelMouse]

As projects go, this couldn't get much simpler. I plan to take a board, maybe 1 X 2.5X 18", embed some rare earth magnets in the back side and hang it on the wall as a knife holder. I'm thinking I'll use a forstner bit to drill out the back side within about 1/8" of the front surface. I'll size the holes to whatever magnet diameter I choose and then I'll cover the back with matching wood. My question is, without building a prototype, I have no idea how many magnets, and what size, depth, hole pattern etc. would best serve my purpose. I'd like it to hold everything from a paring knife to a cleaver - securely, but not so securely as to require two hands to pull the knife from the board. Any advice appreciated!

Check your knives first.  Some alloys are really tough to get a hold of.  

If your knives are high-carbon steel and will stick, I'd go cheap with cow magnets and bore holes, space with dowels if you need two per blade.  Remember to put a ledge on the bottom, so the knives can't fall.

[ed kerns]

Thanks everyone for the input. I've checked out Lee Valley's info. and have been reading up a bit on magnetic properties. This project was requested by a friend of  a friend (I find I do a fair amount of work for other folks, but I'm still not comfortable with "client".) I think I'll just build one from a scrap board and experiment a little.

[smithgl12]

Something like this .5" long x .5" diameter cylinder should work. 13lbs of force
https://supermagnetman.com/collections/n...1410253315

Based on a quick test of holding (vertical like a knife rack) my Leatherman Wave (420 stainless steel) (8.5oz) with a .25x.25 Neo cylinder on the blade. I also tried a .5x.5.x.25"square Neo. That held through 1/16" paper but not through 1/8". All rough ruler measurements. But should get you in the ballpark.

Might want to reduce distance to the knife <1/8". Also I'd "drill" to the face of the holder using a flat bottomed bit on a plunge router. The forstner point might punch through if you go too thin.

[ed kerns]

Something like this .5" long x .5" diameter cylinder should work. 13lbs of force
https://supermagnetman.com/collections/n...1410253315

Based on a quick test of holding (vertical like a knife rack) my Leatherman Wave (420 stainless steel) (8.5oz) with a .25x.25 Neo cylinder on the blade. I also tried a .5x.5.x.25"square Neo. That held through 1/16" paper but not through 1/8". All rough ruler measurements. But should get you in the ballpark.

Might want to reduce distance to the knife <1/8". Also I'd "drill" to the face of the holder using a flat bottomed bit on a plunge router. The forstner point might punch through if you go too thin.

Thanks for this. Yes it was my thinking to go  as thin as is practical on the front surface and the router is a good idea. I also have some cheapy forstner bits, I could drill most way through with a good bit and grind the tip of a cheap one to finish the cut. Or conversely use bar magnets and rout out the entire recess. Part of the equation is finance. The board is basically scrap, but  (as someone mentioned) it makes no sense to spend a fortune on magnets for such a simple project.