WoodWorks by Garry


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Jointer knife / blade sharpening jig

One afternoon while I was about to flatten and square up some white pine to make an exterior door for the garden shed that I was building for my wife, I discovered the knifes that I had in my 8 inch jointer would not cut true across the 7 inch wide boards that I was trying to true up.

The problem was my knives were not ground straight on the cutting edge. They made a fairly good cut when jointing on edge but not on a wider surface.

Well at that point I needed a quick fix. I had to come up with a way to straighten and sharpen the cutting edges myself. It turns out that I am very happy with the way the knives turned out after sharpening them with my simple shop made jigs I made that afternoon.

Below are photos of the sharpening jig and the fence that I made to keep the knife jig square to the inch plate glass that I use for a flat surface. This is a foolproof way of sharpening the blades because of the flat surface and down pressure put on the blades cutting edge. I started out with a coarse emery cloth to get the cutting edge straight and progressively switching to finer sand paper to 600 grit wet or dry sandpaper.

Most photos will enlarge by clicking on them

The knives came out so straight after I was done sharpening them that I could only see a defect free line when I set them on the bench with the cutting edges facing each other. My jointer never cut this True and effortlessly as it did after installing the knives that I had just trued and sharpened. 

With a saw blade that would cut an 1/8 inch curf I set the tilt on the saw at 45 degrees.

Then I ran the 5/4 piece of maple standing on edge through the saw

I cut the length of the fixture
I cut the block of maple about 1/16 inch shorter than the blades and screwed a scrap piece of poplar on each end to hold the blade in the block. By cutting the block just a little shorter than the blade, it allowed the blade to be secured in the block of maple by tightening the screws on the end that go through the poplar end pieces.

Blade secured in the fixture by tightening the screws on either end

Then I made a fence or guide which allows me to slide the block of maple against it to keep the knife edge square to the glass I am using as a surface plate. The sandpaper is setting at an angle to the fence to allow more movement for 8 inch knife length. This would not be necessary with 4 or 6 inch knives.

My hand is resting on a piece of plywood that is secured to the bottom of the guide which allows me to naturally apply down pressure and also keeps the sandpaper flat.

I added the dowel on the top of the block to have something to push against when sliding the fixture back and forth against the fence.