Convex Knife Sharpening with a Belt Sander

I made this series of videos for a contest that was going on with the chance to win three Bark River Knives, and the title “Convex Grindmaster.” So, hopefully that explains the cheesy little intro.

In general, I think the videos are a little cheesy, but hopefully they get the point across. Watching and editing them made me realize that I say “you know?” and awful lot :D

One important thing to note is that I have slightly changed something since making the videos. In the videos I kind of downplay taking the knives through every single last polishing step. Now, I use my finest compound on leather belts EVERY time I sharpen a knife. I think that is important, so just remember that when watching the videos. And, if you have any questions, there is a FAQ section or you are always welcome to shoot me an e-mail at briangandrews at comcast dot net.

Introduction

Welcome to my video series on convex knife sharpening with a belt sander. I have tried to put some thought into the structure and the layout of the material presented. Therefore, I have created a series of smaller videos that build upon each other, rather than making one massive video that will be too large to watch through the web.

I have tried to explain all the key points within the videos themselves, and do not feel that I need to re-explain things in text too. But in order to aid you in directly finding the topic you want, I will make a list of key points for each video. So, let’s get to it.

Intro Video Summary:

- Just introducing myself in this short video.

Testing Knife Sharpness


There are several ways to test for sharpness detailed in the video. They include:

- Using arm hair (least favorite).

- Testing for stickiness on thumbnail. I use this most often. This method will allow you to test ALL sections of the blade. I generally keep laying the blade down flatter and flatter until it no longer sticks. This gives you an indication of relative sharpness too.

- Looking for edge imperfections. A bright light source (sun, window, lamp) will produce a reflection off an area of the blade that is no longer sharp.

Equipment Overview

Key points from this video:

- I use a 1×42” belt sander.

- I prefer the 42” sander because x-weight belts are readily available.

- The x-weight belts are stiffer, and have fewer tendencies to roll as you approach the knife tip.

- I bought my x-weight (Klingspor) belts from Pop’s Knife Supply in Georgia.

- For anything finer than 600 grit, I switch to a leather belt pre-loaded with compound.

- Leather belts can be purchased from Lee Valley.

- Compounds can be purchased just about anywhere you can buy Bark River knives.

- I pre-load my leather belts with compound on a hard surface before putting them on the belt sander.

Sharpening Tips Video

Key points from this video:

- Sometimes when sharpening on a belt sander, getting the edge nearest the handle can be difficult.

- My technique for overcoming this is to angle the tip a little bit away from the belt sander, and give 2 or 3 “false starts.” This will end up with a more even overall grind.

- The tip can be another problem area. I generally do not run the tip much past the mid point of the belt. In doing that, it does not get as much “sharpening time” as the rest of the edge.

- In order to overcome that, I will just run the tip section of the blade a couple extra times.

- I always finish any sharpening grit with one full pass of the knife edge.

- The final tip is regarding the motion used. I demonstrate in the video the motion that is necessary to get a nice, even grind.

Sharpening Stage 1

This video is meant to demonstrate the steps I take to restore the “bite” to a well used edge.

Key points from this video:

- To demonstrate the use of the leather belt, with compound.

- To help with the sharpening angle in this stage of sharpening.

- Demonstration of result.

Sharpening Stage 2

This video is meant to show the next stage of touch up. If the edge is not only no longer sharp, but contains extreme dull spots, or even rolls, you may have to take your sharpening up to this next level.

Key points from this video:

- Belt grits used for this type of sharpening.

- To help with the sharpening angle in this stage of sharpening.

- Demonstration of result.

Advanced Sharpening

I believe this video goes beyond the scope of the contest. So, it is just provided here for bonus material.

My intentions are to show a more aggressive sharpening that can either be used to repair larger edge chips, or to establish a convex secondary bevel on a knife that does not already have one.

Key points from this video:

- Belt grits used for this type of sharpening.

- To help with the sharpening angle in this stage of sharpening.

- Demonstration of result.

- Other uses for sharpening equipment.

FAQ (no video provided)

I have tried to come up with a list of questions that I had as a beginner, and tried to address them here.

Q: What are the advantages of a 42” sander over a 30” sander?

A: I like the 42” sander because x-weight belts are readily available for it. The x-weight is a stiffer backing, and less tendency to roll when you reach the knife tip. This rolling occurs because of equal pressure being applied to the belt, then as the knife edge ends (at the tip) a lighter belt will roll on you. I think that you can still do things just fine with a non-x weight belt, but it will require more technique and practice.

Q: Are leather belts necessary?

A: No, this is my preference to use these. I know many people, especially with a 30” sander that will use really fine grits, like a 15 micron belt. Whatever works, the results of either are pretty comparable.

Q: Is there any practice you recommend for beginners?

A: Yes. Do not start out on your most cherish knife : ) Go buy a couple cheap clunkers, like a Cold Steel Bushman and grind away on those. Practice the techniques I have shown until you have them down. Then move on to your better knives. Another tip is to do your practicing with a finer grit belt than you think you actually need. Every pass on the belt does not remove as much material. That way, you can get a feel for what your are doing, and see the effect on the edge without grinding away a lot of metal. If you start with a real aggressive belt, one pass can do a lot of removal. Get the feel for things with the fine grits.

Q: How do you keep from dulling the knife tip?

A: In general, I do not grind the tip the full width of the belt. I get it just a bit past the halfway point, and I stop. Even the stiffer belts will start to twist on you if you take them too far across the belt, and it is not worth knocking the sharp point off. If the tip does not get as much grind as the rest of the edge, I will run just the tip a couple of times alone, always finishing with a full edge pass on the belt.

Q: How do you know what angle to hold the knife at?

A: This is a very difficult question to answer, because my answer is based on experience and has multiple parts. So, let’s address those parts.

Answer 1 (for touch up work): This is the easier one to answer because you are not going to be using aggressive sanding grits, and not trying to create a new profile. So, what you want to do is match the angle that is already on the knife. With your belt not running experiment with the angle that gets the edge to just barely touch the belt. Remember that angle and practice it. Then, turn the sander on and go at it. Err on the side of being too shallow, and inspect the edge for results. If you are not quite getting to the edge, increase the angle until you do sharpen all the way to the edge. If you are only using a leather belt, you can almost tell the correct angle by sound, as demonstrated in the video.

Answer 2 (grinding new edge): This is the difficult one to answer. I don’t try to get all into measuring angles, and getting an EXACT angle. The best I can say is that from experience, I know approximately what angle to apply to what type of steel, and that is close enough for me. I will evaluate the result after I am done, and if it is not what I like, I will go back and grind so more. In this case, you are better to err on the side of too steep of an angle, rather than too shallow of an angle. The reason is it is always easier to take more material off, rather than trying to put it back. So, if you grind an edge and it is about 20 degrees on high carbon steel and you feel it is still too thick and not sharp enough, then go back to the belt sander and decrease your angle to about 15 degrees per side. This is the area that practicing on cheap knives really help.

Q: How do you keep a consistent angle?

A: This can take some practice, but really does not take long to get the hang of. Once you have practiced the sharpening motion required, shown in the “Tips and Techniques” video, it become pretty easy. When I decide on an angle, I look at the distance between the knife spine and the belt. I just concentrate on keeping that distance consistent, and move the knife with a fluid motion. Looking at the edge should show you a nice consistent grind, letting you know you did everything correctly.

Q: What belts do you use?

A: For gritted belts, I use Klingspor x-weight belts in 220 grit and 600 grit. I usually can do all my gritted belt work with just those two. In order to get a high polish, I use leather belts pre-loaded with compound.

Q: Where do you get your belts from?

A: I get my gritted Klingspor belts from Pop’s Knife Supply. I get my leather belts from Lee Valley.

Q: Where can I get compound from?

A: Pretty much anywhere you can get Bark River knives from, also carry the Bark River compound. If you still can not find that, both Pop’s knife supply and Lee Valley carry different compounds. If you are looking to buy local, places like Production Tool Supply, and most woodworking stores carry compounds.

Q: How do you apply compound to your leather belts?

A: I put the belt down on a hard surface, and rub the compound in. If you are having difficult with that (especially when the belt is new) you can try a small amount of heat to the compound (lighter, hair dryer, heat gun, etc). If you get too much on the belt, the worst thing you are going to do is make a mess when you fire up the sander.

Q: Do you heat the blade enough to ruin the heat treat?

A: The short answer is no. After every pass or two, I will touch the edge with my fingers to make sure it is not warm. If it is cool enough for me to not notice any significant heat, it is not going to bother the heat treat. If you start to notice the edge is too warm, you can use a bowl of water to dip the knife in to keep it cool. Just make sure to fully dry it before sharpening again.

Q: Do I really need a belt sander?

A: There are other non-motorized methods for sharpening, and a whole different category to cover those techniques. But, everything shown here can be done by hand, it is just going to come down to a matter of time. If I have a ding in an edge, it could literally take a couple hours or more to work out my hand. With a belt sander, I could easily be done in less than 10 minutes. The belt sander also gives me the confidence to know that there is no amount of damage I can not fix. So, I do not hesitate to beat on stuff. If I knew it could cost me 6 hours of time, I might think twice about beating on something : )

Q: What does the final finish of the edge look like?

A: I like a real, real high polished edge, and not the more saw tooth, jagged type of edge that some prefer. I like the high polish because based on my experience, it seems more durable, and holds up better. I also like the way it will push cut material, rather than requiring a slicing motion to do the same thing. The high polish also makes touching up the edge by hand rather easy.

Q: How large of a knife can you sharpen this way?

A: As big as you want. Nothing changes, not even the technique. In fact, I think bigger knives are easier. The trickier ones are the super short ones. On those, all the little “techniques” have to happen in a shorter period of time, and sharpening angles can be harder to determine. It is still easily done though