Guided knife sharpening jig

Part 2: Guided knife sharpening jig - prototype

As a proof of concept, I built a prototype. I don't think the final product will look or function exactly like this, but this at least helps me see if the jig will function like I want it to and give me the opportunity to tweak anything in my design before I commit to the final, more costly materials.

I made this version out of some white oak I had laying around.


I like the idea of using a threaded rod to adjust the sharpening angle. Most kitchen knives can be sharpened to 20 degrees on each side (40 degrees total included angle), but some specialty knives have 10, 15, or 25 degree bevel angles. Being able to change the angle easily, accurately, and precisely was one of my design requirements.

In the prototype, changing the angle is accurate, precise, and repeatable, but it certainly isn't easy - well, it's not hard, but it's a pain to screw the top nut up to the desired height, then screw the bottom one up - or vice versa. I'll need to come up with a more convenient way to do that.

The abrasive (either diamond hone or emery paper on a glass plate) will mount to the angled rod. The knife will be held in place by the rare-earth magnets embedded in the base. After trying it out I determined I will need to come up with a way to accommodate knives of varying lengths.

The mounting point on the threaded rod does allow for all the necessary degrees of freedom, but I think there is probably a more elegant solution. I'm thinking some sort of ball joint - sort of like a tie-rod end would be slick. I'll scour McMaster to see what they have.

I've got a pretty good idea about the basic design. Next I'll dig through the wood pile to find some nice pieces for the final build.

Starting the fabrication

From the wood stash I picked out some nice curly maple and pernambuco. At least it was sold to me as pernambuco - I have my suspicions that it might actually be chakte viga. It is way more vibrant than the pictures indicate.



I milled them to size. The three smaller pieces of pernambuco will allow me to have a mounting surface of various width for various length knives. You'll see how that works out later on.



I then milled grooves and tenons (?) so the three mounting pieces would fit together and remain perfectly flat but be easy to separate when I need a shorter surface.





And here they are all fit together…


Those 3 pieces all need a way to connect to each other and to the base. Pernambuco is pretty hard stuff, so I drilled and tapped some holes so they can all bolt together with 1/4-20 socket head cap screws.





Next, we'll make the holes in which to mount the rare earth magnets, and start working on the base and uprights.

The base and uprights

I finished up the rest of the milling on the base. I drilled the holes for the rare earth magnets (they are neither a nice round English or metric size). I think I ended up using 31/64" for a good snug press fit in the prototype. I milled the notches for the uprights, and the holes for the threaded rod bushing and what I'm calling the guide rod. The guide rod will help keep the 'carriage' square as it moves up and down. I'm not sure if it is strictly necessary, but in keeping with my 'needlessly complex' design, I figured I'd add it.



I added some sacrificial blocks on either side of the based to prevent chip out.


Dry fitting uprights in the notches:


I then made the holes for mounting the uprights to the base. They'll be mounted using 1/4-20 socket head cap screws. I milled the holes for the threaded rod bushing and guide rod in the top piece. Then I routed the finger joints for the top and uprights using my Incra fence. And








That finishes the fabrication of the wood parts (well, almost). Next I move on to machining the other bits out of Delrin, bronze, steel, stainless steel, and brass.

More fabrication

I've done a lot of fabricating of the parts for the knife sharpener, not just of wood but as you'll see, Delrin, stainless steel, and bronze, too.

I milled out the spots for the uprights, drilled the holes for the magnets, and did a test fit.




I milled the finger joints for the uprights on my router table with my Incra fence.





Then I turned my attention to the other parts. I started with the treaded bushing in which the threaded rod will turn. I turned it from 1/2 bronze bar stock.


Then I knurled it to give it a good rough surface for the press-fit into the carriage.


Here it is with the carriage blank roughed out and two other pieces we'll see later.


After a little more machining and the use of the hydraulic press, we have a good snug fit of the bronze threaded bushing in the Delrin carriage.



With the carriage done, we move on to the abrasive stone holding assembly. I first tackled the bushings that will serve as stops on the stainless steel rod. The rod will be the piece you grab and move back and forth to actually do the sharpening. The bushings are machined out of stainless steel.

Here it is being parted off on the lathe, followed by drilling and tapping for a 6-32 set screw.




And here is the general idea of how it works. The rod slides through a rod end in the carriage that allows rotation in all directions up to 27 degrees. Bushings with springs on either end of the rod end provide soft limits to the travel of the rod forward and back. The Delrin block on the top is part of the assembly for holding the abrasive stones. It is held in place by a similar stainless steel bushing.



I wanted a way to consistently and accurately set the angle. I decided to use my digital angle gage to do that task, but I needed a way to hold it in place while I was adjusting the angle. The angle gage has magnets built in, so I came up with just embedding a steel disk in the abrasive holder block. That way while I am setting the angle the gage will just set there and I can read the number to determine when I am at the right angle. I knurled the steel disk just like the bronze bushing before to allow for a good snug fit in the slippery Delrin.



Next I made handles so I could easily grab and control the rod/sharpening stone assembly either from the end or from the top. I made them out of a small scraps of pernambuco. I cut the head off of two socket head cap screws and knurled the ends, then super-glued them into wood handles for easy mounting on the rod assembly. The spring provides enough force on the sharpening stone to hold it in place against the other Delrin block (which is held fixed by a bushing on the rod), but also allows for quick and easy swapping out of stones for other grits - just compress the spring a little and remove the stone, insert the new stone, release the compression, and viola.











And here are the handles installed on the rod assembly.


Next I'll make a knob for changing the angle and I'll to the first test fit of all the components I've made so far.

Making the knob and feet, and assembly

The next step in the saga of the knife sharpener is to make a knob from a small scrap of pernambuco.


I machined a small stainless steel sleeve I'll use to mount the knob. I knurled the end so it would bind securely to the hole drilled in the knob. I added a little superglue to help.




With the sleeve mounted in the blank, I could hold on to it in the collet of the lathe. I turned a small 'divot' on the surface of the knob, just for aesthetics.

Then, using the dividing head on the mill I machined seven 'scallops' in the knob's edge to give something to grab on to when turning it.




And here is the first dry-fit with most of the parts complete.


Next I cut out the pieces for the feet using a hole saw, and turned them to final shape on the lathe.









Next up was to spray a few coats of General Finishing Enduro gloss.


And final-ish assembly.


I'll use it for a bit and see how I like it. I'm sure there will be a couple tweaks coming…

FancyLearnin said:

Making the knob and feet, and assembly

The next step in the saga of the knife sharpener is to make a knob from a small scrap of pernambuco.

I machined a small stainless steel sleeve I'll use to mount the knob. I knurled the end so it would bind securely to the hole drilled in the knob. I added a little superglue to help.

With the sleeve mounted in the blank, I could hold on to it in the collet of the lathe. I turned a small 'divot' on the surface of the knob, just for aesthetics.

Then, using the dividing head on the mill I machined seven 'scallops' in the knob's edge to give something to grab on to when turning it.

And here is the first dry-fit with most of the parts complete.

Next I cut out the pieces for the feet using a hole saw, and turned them to final shape on the lathe.

Next up was to spray a few coats of General Finishing Enduro gloss.

And final-ish assembly.

I'll use it for a bit and see how I like it. I'm sure there will be a couple tweaks coming…

Click to expand...

Excellent work! I've followed your progress on this build and I really like the design you came up with. I also appreciate your methods Having a metal lathe and milling machine and knowing how to use them sure is a nice thing isn't it? I like how you used a lead screw to position the carrier block to set the angle.

I'm curious if you're just relying on the magnets to secure the knife or if there will be other clamping? Also, I may have missed it, but what kind of threaded rod did you use for the carrier block and is there a set screw or anything to lock the position or are the threads the sole retention?

I've often pondered making either something like this or a clone of the Wicked Edge system. But, it's never been a top priority and my Lansky kit and Worksharp seem to always keep it on the back burner. Welcome to the site and thanks for posting such a great blog series to introduce yourself!

FancyLearnin said:

Making the knob and feet, and assembly

The next step in the saga of the knife sharpener is to make a knob from a small scrap of pernambuco.

I machined a small stainless steel sleeve I'll use to mount the knob. I knurled the end so it would bind securely to the hole drilled in the knob. I added a little superglue to help.

With the sleeve mounted in the blank, I could hold on to it in the collet of the lathe. I turned a small 'divot' on the surface of the knob, just for aesthetics.

Then, using the dividing head on the mill I machined seven 'scallops' in the knob's edge to give something to grab on to when turning it.

And here is the first dry-fit with most of the parts complete.

Next I cut out the pieces for the feet using a hole saw, and turned them to final shape on the lathe.

Next up was to spray a few coats of General Finishing Enduro gloss.

And final-ish assembly.

I'll use it for a bit and see how I like it. I'm sure there will be a couple tweaks coming…

Click to expand...

Thanks for the kind words. The magnets are the only means of securing a knife on the jig. I'd thought about using some sort of a clamping mechanism, but I wanted good clearance for shallow sharpening angles (such as for filet or santoku knives) and most clamping schemes just sort of get in the way. I bought the strongest classification of neodymium magnets (N52), and I ordered thicker ones than I normally would have so they have higher magnetic flux. They are incredibly strong. The knives, even long and wide ones, are held extremely well. In fact, you have to be very careful removing a knife - you really have to pull. My technique is to tip the knife up on edge (the back edge) so there is less area in contact with the magnet and then pull it off. That works quite well.

The threaded rod is 3/8-24. I wanted a fairly fine thread so that I would have a good degree of precision in setting the angle. The flip side of that is you have to make a lot of turns to significantly change the angle. I anticipated that, and it was a trade-off I was willing to make. Fortunately I don't need to change the angle too much since most kitchen knives have the same angle, you only need minor adjustment to compensate for the width of the knife.

There is no set screw to lock it in place once the angle is set. It doesn't move at all when sharpening. I had thought about adding some sort of locking mechanism, but it turned out not to be needed at all. And the thread is so find that even if it did move it would be insignificant to the sharpening angle.

I had put this project on the back burner for a long time, but eventually my frustration with dull knives overcame my inertia. Plus I had to work out the design in my head, given the design criteria I had set for myself. I had not seen anything that works exactly the way this one does (though I am sure they are out there), so I did a little head scratching to start. I didn't have any means of sharpening knives before - other than freehand, which never seemed to turn out too well for me. Now my knives (and scissors - more to come on that application) are razor sharp and I go around the house looking for things to sharpen!

Tweaks and upgrades: The last chapter

Having used the sharpening jig for a bit, I decided to tweak a few things to make it more useful and more user friendly.

The first was to correct a major nuisance. When you want to change our stones/grits, you needed to set the arm down either off to the side (if the knife was short enough to allow for that), or somehow set it down on the knife itself.

I needed a way to 'hang up' the arm out of the way. I first experimented with this solution:


But that wouldn't do. It was too cumbersome to hook the string on the hooks and you could only do it if the carriage was the right distance from the top. A better way was needed to hold the arm that didn't rely on a flimsy string and moved wherever the carriage moved. This is what I came up with. I made a hook of sorts out of some think aluminum sheet, and put a bend in it to approximate a perpendicular angle to the arm when tilted up.











The next thing was the need to adjust the fixed collar positions without the need for a small Allen wrench. I want to have all the major adjustments be able to be done my hand. So I made thumb screws to replace all the tiny set screws.











And the 'major' upgrade was a jig/holder to allow for sharpening scissors. Since most scissors have slightly curved blades, a wide holder like the magnets for knives I have on the sharpener won't work. I need something narrower that can really clamp down on the blades. I made a prototype as proof of concept, but sadly I don't have pictures of it. Anyway, the final version started out with some cold rolled steel.




After some more machining and a little hot bluing, it looks like this:


Of course I can't just leave those socket head cap screws sitting there taunting me, so I made some bronze thumb screws to adjust it.




And that's it! So what do you think? I'm pretty pleased with how it turned out, and I am really pleased with its ease of use. I've sharpened every knife and scissor in my house. Now I should probably make a nice storage box for it…

FancyLearnin said:

Tweaks and upgrades: The last chapter

Having used the sharpening jig for a bit, I decided to tweak a few things to make it more useful and more user friendly.

The first was to correct a major nuisance. When you want to change our stones/grits, you needed to set the arm down either off to the side (if the knife was short enough to allow for that), or somehow set it down on the knife itself.

I needed a way to 'hang up' the arm out of the way. I first experimented with this solution:

But that wouldn't do. It was too cumbersome to hook the string on the hooks and you could only do it if the carriage was the right distance from the top. A better way was needed to hold the arm that didn't rely on a flimsy string and moved wherever the carriage moved. This is what I came up with. I made a hook of sorts out of some think aluminum sheet, and put a bend in it to approximate a perpendicular angle to the arm when tilted up.

The next thing was the need to adjust the fixed collar positions without the need for a small Allen wrench. I want to have all the major adjustments be able to be done my hand. So I made thumb screws to replace all the tiny set screws.

And the 'major' upgrade was a jig/holder to allow for sharpening scissors. Since most scissors have slightly curved blades, a wide holder like the magnets for knives I have on the sharpener won't work. I need something narrower that can really clamp down on the blades. I made a prototype as proof of concept, but sadly I don't have pictures of it. Anyway, the final version started out with some cold rolled steel.

After some more machining and a little hot bluing, it looks like this:

Of course I can't just leave those socket head cap screws sitting there taunting me, so I made some bronze thumb screws to adjust it.

And that's it! So what do you think? I'm pretty pleased with how it turned out, and I am really pleased with its ease of use. I've sharpened every knife and scissor in my house. Now I should probably make a nice storage box for it…

Click to expand...

Fantastic work! A very well thought out and well made design It should serve you well.

FancyLearnin said:

Tweaks and upgrades: The last chapter

Having used the sharpening jig for a bit, I decided to tweak a few things to make it more useful and more user friendly.

The first was to correct a major nuisance. When you want to change our stones/grits, you needed to set the arm down either off to the side (if the knife was short enough to allow for that), or somehow set it down on the knife itself.

I needed a way to 'hang up' the arm out of the way. I first experimented with this solution:

But that wouldn't do. It was too cumbersome to hook the string on the hooks and you could only do it if the carriage was the right distance from the top. A better way was needed to hold the arm that didn't rely on a flimsy string and moved wherever the carriage moved. This is what I came up with. I made a hook of sorts out of some think aluminum sheet, and put a bend in it to approximate a perpendicular angle to the arm when tilted up.

The next thing was the need to adjust the fixed collar positions without the need for a small Allen wrench. I want to have all the major adjustments be able to be done my hand. So I made thumb screws to replace all the tiny set screws.

And the 'major' upgrade was a jig/holder to allow for sharpening scissors. Since most scissors have slightly curved blades, a wide holder like the magnets for knives I have on the sharpener won't work. I need something narrower that can really clamp down on the blades. I made a prototype as proof of concept, but sadly I don't have pictures of it. Anyway, the final version started out with some cold rolled steel.

After some more machining and a little hot bluing, it looks like this:

Of course I can't just leave those socket head cap screws sitting there taunting me, so I made some bronze thumb screws to adjust it.

And that's it! So what do you think? I'm pretty pleased with how it turned out, and I am really pleased with its ease of use. I've sharpened every knife and scissor in my house. Now I should probably make a nice storage box for it…

Click to expand...

Thanks, Kenny! It sure is nice to have sharp knives and scissors again.