Knife grinding magnets???

C

CDH

Joined
Jun 8, 2007
Messages
283
How many use them? I keep wanting to build one with the pile of rare earth magnets I have salvaged from dead hard drives, but I always talk myself out of it...

Now I am getting tired of skinned knuckles trying to flatten tangs and surface grind off the scale from SS barstock. That seems to be ideal usage for a magnet...

SO, long story short, how well do they work and is grinder dust piling up on the blade/magnet a big problem or not?
 
I just use a big speaker magnet. It's not so strong that it's difficult to remove the blade, but holds well enough. I cover it now and then with masking tape to prevent blade marring- the tape can also be peeled off if the magnet grows a large pile of steel dust.
 
i use a magnet from an old vcr. the magnet is from the bottom and is usually connected to a motor by a small belt. mine came from an older vcr about 8-10 years old. a piece of steel will let you know if you have the right one without taking things apart. they are about 2-2 1/2" in diameter but some are close to 3".

an offset handle must be made if you use one that big so you can push on the blade in line and not have the handle off center or have half the magnet hanging over the edge of the blade. a offset for the handle can be made from a block of aluminum with a hole drilled on the end which attaches to the magnet. another hole is drilled to position the handle in the middle half of the magnet.
 
Lee Valley is said to have some powerful rare earth magnets. And for some really incredible magnets, try this outfit. They have one that rates at around a half-ton of pull. They say they require three guys to be working together when they move these beauties around. Friend just got a delivery of some much smaller ones of theirs yesterday that are extremely powerful, yet compact and ready to be incorporated into what I think would make a terrific blade-grinding holder. http://www.kjmagnetics.com/proddetail.asp?prod=BZX0ZX0Y0-N52
 
I actually use a magnet from a laptop drive. The IT section at work had dozens of them so I have a couple on my anvil and one screwed onto a piece of wood to hold blades for flattening. Works great.
 
The ones from Harbor Freight work great. I only use them for tapering tangs. You do have to periodically scrape the dust and shavings off the magnets.
 
I picked up a great 120 lb. pull welder's magnet from Amazon for around $14.00. So far all I've used it for is removing scale from bar stock

Like emphaski, I would love to learn to use it to grind in a distal taper before doing my bevels, but haven't progressed quite that far yet.....
 
I found an old magnetic kitchen knife holder for .50 at a yard sale. It broke down into two 1" x 6" magnets which are perfect for grinding.

Dick
 
Hi all

Sorry for not contributing with messages up to now. :-(

This is my solution:

I have screwed three countersunk neodymium ring magnets to a piece of wood and taped masking tape over the magnets.

Masking tape solves iron dust problem. When you need to get rid of the dust, you can tape an extra layer and remove all the layers with the dust trapped inside.

bicak_b1_09.jpg
 
Here's my recently completed setup from K & J Magnetics. It's got 40lbs. of pull using four magnets. I used to use hard drive magnets, but had trouble fastening them to the handle. These are countersunk and bolted to the 1/2" x 1.5" x 1/2" C channel. It's about 8" long and keeps the blade very flat. I had trouble with shorter magnets. When I got to part of the blade that wasn't right by the magnet, it would flex. Most of my blades(3 of the 4) are 3/32" or 1/16" so it was an issue often.
magnet2.jpg
 
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Rare earth magnets have a heat range they cannot exceed. The ones I use start to break down [lose magnetism] @ 250 fh. They would not be a good choice if you are doing a lot of stock removal where the temps get pretty high.

Fred
 
Build your own. Take 2 pieces of 1/8" steel bar. I think I used 1 1/2". Go to lowes and pick up a pack of their ceramic magnets. 1/2" X 1" X 2" IIRC.
You may have to play with the poles to get the pull right. Once you do, you will know it. You can then wrap in tape leaving the top open and pour epoxy in the middle to hold everything.

One word of caution. Only use 2 magnets. use 3 and you will not be able to get your blade back, not without a vise and plyers. So I hear:rolleyes:

Paul
 
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