Jointer Knife Sharpening Jig

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Project by measureagain posted 05-15-2015 02:59 AM 1327 views 9 times favorited 2 comments Add to Favorites Watch

This is one of my favorite “tools”.
I like to keep my jointer knives sharp, in between the major honings to remove nicks. I read an article a few years ago in Finewoodworking on how to sharpen them in place. It used a dowel in a wood block to index the slots in the cutterhead. Looked great, except that it only worked on real jointers like a Powermatic, Delta, Jet, etc. The geometry of my Craftsman jointer didn’t have enough clearance for that solution to work.
My solution was a custom fit wood block with a slot in it to slide a z-shaped piece of fiberglass down to lock and index the cutter head.
Your dimensions may need to be adjusted, but this is what works for my particular jointer. I have used it many times, and it keeps the knives tuned razor sharp, and all cutting evenly.
I started with a wood scrap cut to 3-9/32” L x 1-5/16” W x ¾” T. One of the corners needed to be slightly rounded with a file for a snug fit. It has to fit tight to give repeatable results. On the front of the block is a slot cut at 55 degrees, which on my jointer will position the knives just slightly past TDC. It is a half inch deep, and in my case just a hair over .2” wide.
The sliding piece that indexes the cutterhead needs to be durable, and not affected by temperature or humidity. I laminated several pieces of copper clad fiberglass, but you could use a piece of aluminum, or whatever is on hand. My lamination ended up .2” thick. Whatever thickness you end up with, that is the starting width of the slot in the wood block. Fine tune the slot with a file so the material can slide in the slot, but not without some effort. If anything ends up sloppy, you will not get good results.
I had to cut and file my sliding piece into a “Z” shape in order to give me access to the full width of the knives.
It works like this:
First, make sure the jointer is unplugged. Second, check that again. Next, cover the first 12” on the outfeed table with a layer of packing tape, to protect it from the diamond plate. Drop the infeed table a half inch to get it out of the way. Remove the cutterhead guard and set the wood block next to the cutterhead. Raise the infeed table to snug the wood block into place so it will not move. Rotate the cutterhead and carefully slide the z-shaped piece into the slots in the wood block and the cutterhead. If you aren’t going to be careful, keep Band-Aids handy. The outside edge of a jointer knife is almost always still extremely sharp. Place a straightedge on the outfeed table to see if you have to slightly lower it (packing tape thickness). Use a long diamond plate and hone the knife, working the full width, and counting strokes. Pull the z-shaped piece, and rotate the cutterhead to the next knife. When all knives have been touched up, remove the index block and packing tape, reset the outfeed table if you adjusted it, and reinstall the guard.

2 comments so far

View splintergroup's profile


737 posts in 646 days

#1 posted 05-15-2015 02:28 PM

I have made the same jig for my Jet jointer. This has to be the ‘best’ tool there is for sharpening and setting knives.

The angles are perfect, you can easily cut a narrow relief bevel, the knives are left perfectly aligned with the infeed table, all without breaking a sweat. No need for fussy blade setting fixtures and other doodads.

View Lumberpunk's profile


323 posts in 1760 days

#2 posted 05-16-2015 07:01 AM

very cool… on my todo list… thanks!

-- If someone tells you you have enough tools and don't need any more, stop talking to them, you don't need that kind of negativity in your life.

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