Guided Angle Sharpening a Spyderco to the Plunge, Using 3D Printing Parts

[Dutch87]

I bought a M4 steel Spyderco Tenacious recently, and when I bought it I was too distracted by some other knives I was buying at the same time to notice that when it was sharpened at the factory, they left a few mm extra unsharpened right before the plunge line. The edges on Spyderco knives always run into the plunge, and the bevels stop a millimeter or less from shoulder, but this was much more than usual.
You can see in the picture that between 3-3.5mm was left unsharpened.

I wanted to fix this when I put my own edge on the knife with my a guided angle sharpener, but I knew that if I simply started grinding against the plunge it would create uneven areas underneath the stone and where the edge of the stone was eating away at the existing bevel and that these defects would be extremely difficult to even out. I figured that the best way to bring the unsharpened portion of the Tenacious blade even with the existing bevel was to grind on it with something that was no wider than the unsharpened area was.
I have a selection of ceramic and india stone files that are about a ¼" wide that are about the right size for the job, but since this was M4 steel I expected it to be resistant to fine grinding and wanted to use something more aggressive I have some of the Spyderco Sharpmaker triangular stone sets including the CBN plated set so I decided to use these. The rounded "point" of the triangle stones are under a millimeter wide and it can get right into the corner of the blade and the plunge.

I prefer to use a guided angle system to sharpen, so I didn't want to freehand the stones against the blade. I wanted to mount them in the dovetails of the system's stone holder, so I decided to design and 3D print an Edge-Pro compatible mount for the Sharpmaker stones.
I went the Thingiverse.com to browse for existing 3D designs that might give me a jumpstart and I found that Leading Edge had uploaded a Sharpmaker holder design for a Lansky sharpener a few years ago, His design had then been modified and re-uploaded by someone else to support the triangular stones in more places. I took that remixed design and changed it to be part of a 1" x 8" base with 45 degree bevels in the ends for Edge-Pro mounting. It took some prototyping, but I got a design printed that is stable and secure and centered on the guide rod of my sharpener.

Here is a Sharpmaker CBN stone mounted on my TS Prof K03 rod with the 3D printed holder.

I disassembled the Tenacious and mounted the blade in a single milled clamp by the ricasso. For full flat ground blades I usually disassemble them and clamp them this way. It is more accurate and secure.
I thought that putting an 18 degree per side edge on the Tenacious was a conservative target, and I hoped that I could grind in the unsharpened heel of the blade at that 18 angle and then switch to my main stones for the rest of the sharpening and keep a consistent angle across the entire blade.

I use the K03'S built-in digital angle finder, but because round or triangular stones cannot sit flat on the blade, they can throw the digital angle finder off since they have be held upright. So I'd rather adjust the sharpening angle with something that can sit flat and then swap the triangular stone in. So first I used a flat, narrow ceramic file in another 3d printed mount to set the 18 degree angle. You can see some more 3d printed parts I made to give me a better surface for using the K03's coarse adjustment rod for thickness compensation. Every time I will switch to a new stone, I will drop the round "hat" onto the stone and tighten the K03's coarse adjustment there to include the thickness of the stone in the setup of the sharpening angle.

Then I change the thickness for the much taller Sharpmaker stone and mount.

Here is the Tenacious blade prepped for surgery. I taped off the rest of the blade that I don't want to hit with the CBN triangle.

I realized that I had clamped the blade in at a bad rotation. I clamped the blade with the tip pointing perpendicular to the extension of the clamp the way I normally would, however with this sharpening, getting the stones to shoulder up all the way to the squared off plunge line is paramount. So I had to rotate the blade in the clamp until the straight line of the stone aligned with the plunge. Of course moving the blade in the clamp threw out my angle setup from earlier, but it should still be close.

In this picture, you can see that the CBN triangle was very effective in putting a bevel on the unsharpened section, but the small bit of material that dips down below the sharpened edge like a turkey wattle was preventing me from getting that last half millimeter ground in.

So I decided to take the CBN triangle out of the mount and free hand it like a file and come in perpendicular to the blade to cut that wattle off. I don't have pictures of this, but it was effective, if overly aggressive. I cut that tiny section out, then used the ceramic files to smooth out the face of the ricasso that I had ground into.

Once the wattle was gone and the previously unsharpened area had been sharpened to some degree, I set up the thickness of the main stones I would be using: Venev Ursa Diamond Resin.
These stones are shorter than the 6" Edge Pro standard, and don't have 45 degree cut ends for dovetail mounting because they are double sided. I use them because they are just a bit over ½" wide and I feel that narrow stones make it easier to even out the grind on a blade with variations or defects in the heel from a bad factory belt grind, especially if the edge runs into the plunge and you cannot overshoot the heel like you can with the tip to make sure you can reach all of it.
I reset the angle to 18 degrees and sharpened from 150 grit to 800 grit. Since I had rotated the blade to align the straight lines of the CBN triangle with the plunge line, the rectangular Venev stones were able to reach all the way into that heel corner.

For stropping, I set the thickness in my angle adjustment to a sanded piece of basswood treated with 1um diamond emulsion mounted to a ½" aluminum blank. I backed the adjusted angle off to 17.7 to avoid rounding over the sharpened apex.

Here is the sharpened and stropped blade still in the clamp, and then reassembled.

You can see a tiny scallop cut into the heel almost at the extreme corner. I believe this was a result of the CBN being much more aggressive on the M4 steel than I anticipated, and the attempt of filing away that turkey wattle got ahead of me. This was the only blemish in the bevel finish that remained from the incomplete factory sharpening and my experiments. Honestly, to have any imperfection in the bevel after so much work and preparation is disappointing, but I believe that will be erased by the next sharpening.

I think I should have attacked that turkey wattle at the heel first, and with slower ceramics before trying to put a bevel on the unsharpened area. I probably didn't need the CBN at all with this blade. I will revise my Sharpmaker mount 3D design as well, as I realize that it is wider than it needs to be and was a bit hard to see around to the work when I was grinding in that corner.

Thanks for reading. I always enjoy sharpening and challenging myself to try new methods on different blade styles.

 

[bmo419]

I love 3D printers for addressing stuff like this when there's no solution that currently exists. That little unsharpened section on Spyderco's is pretty common though in my experience. If anything it's been more rare for me to get one sharpened all the way down to the plunge. I'm in the same boat that I also don't like the little unsharpened section and just sharpen all the way down to the plunge, though I freehand so it's a bit easier in my case. Stones with a 90 degree edge like your Venev's would've worked better than the Spyderco CBN as you found, particularly because Spyderco usually does a 90 degree plunge so it fits in there nicely. Nice that you got it solved though.