Backyard forging part 5: Sharpening

Process of sharpening a knife:

The task of getting a fine cutting edge on to your knife is an important element to the knife-making process, arguably one of the most important. Regardless of how refined and aesthetically pleasing you are able to make your knife it is only worth its salt once you have a sharp and robust cutting edge. This is the business end of the tool at the end of the day.

All this being said I am not going to spend hours describing the finite details of how to achieve the sharpest cutting edges as there’s a great number of people already doing so out there on the internet and through other mediums. Instead I will cover the basics of what you want to be aware of and how to achieve a serviceable cutting edge to your bushcraft knife.

The science behind the process:

Whenever we are sharpening a knife or any edged tool for that matter it helps if we have an appreciation of what is going on along the cutting edge at a microscopic level. This allows us to better achieve the end result that we desire.

Once the edge of a tool has dulled, or is yet to have its cutting edge applied, what looks to the naked eye to be continuous sharp edge will in reality consist of a series of burs and look like a microscopic saw edge. It is these saw teeth that we are gradually aiming to reduce using a series of finer grade abrasive surfaces. Notice I said ‘abrasive surfaces’ instead of a specific type of sharpening stone. I will explain why shortly. This moving down through the different grade surfaces continues until we are at such a level that we can cleanly remove the ultrafine burs through a process known as stropping which will be covered at the end of the blog.

Importance of angles:

Briefly I want to discuss the different cutting edges that we can achieve when profiling and sharpening our cutting edge. There are three broad types of cutting edge; Concave, convex and flat or Scandinavian edges. All three have their merits and disadvantages and there is a wealth of literature out there for those interested in the subject.

Three main profile options for our knife bevel; Convex, Concave and Scandinavian grind 

 

Through the rest of this blog I will focusing on obtaining and sharpening a Scandinavian grind as through experience this is the most versatile edge for a range of bushcraft activities and allows for ease of maintenance when out in the field.

Working through varying grits:

As already stated above the whole process of obtaining a workable cutting edge is one of moving down through progressively finer abrasive surfaces. The reason I say abrasive surfaces is due to the nature of this knife making process, one where we have been trying to use what we will find at home or in the shed, we won’t necessarily have a range of specific tools for the job. This is in no way a fact that should hold us back and one that we can easily overcome utilising a range of common and cheap, household items.

Selection of tools used to obtain a keen cutting edge

Our home made knife is now ready to have its cutting edge applied to it and as we are starting completely from square one we are going to have to start at that very point. One which is very much courser than we would ever use to re-touch an already sharpened knife that has simply lost its edge.

The first sharpening tool that we are going to use is a flat metal file. As I said this is an extremely abrasive tool and should be used with caution so as not to unintentionally remove material. It will however allow us to really profile on the bevel of the blade to the desired angle before we swap over to finer and more time consuming means of sharpening.

Flat file being used to profile the bevel onto the knife

At this stage you are aiming to profile the correct angle, somewhere between 25 to 28 Degrees for the entre cutting edge. This will result in each side of the bevel being a 12.5/14 degrees drop in angle to the cutting edge. This can sound tricky and rather precise to achieve but really don’t let yourself get hung up on the issue. It has to be near those figures but not exactly, although the nearer the better. Just so you know I didn’t spend hours with precise measuring equipment attempting to get the angle exactly right, I simply had one of my existing knives to hand and made sure that my home-made knife mirrored that as closely as possible.

A good tip here is to focus on how far the bevel of your existing knife travels up the blade. This is what will determine the angle along with the thickness of the blade. So for example if your blade is 2mm thick you should aim for a bevel that is between 4mm in depth, i.e. 4mm up the face of the blade.

Relationship between blade thickness and bevel height

Now that we have established a good working profile for our knife it is time to proceed to sharpening it. Throughout this first sharpening stage, we will have to start with a relatively course grit stone or sand paper depending what you have to hand. If you have not got any specific sharpening stones or fine files then getting hold of a pack of sanding belts means you can make your own sharpening blocks for a few pounds, if not pennies. This is achieved by a block of wood being inserted into the belts and two small chocks to tension it for a flat sharpening surface.

The process that I shall now describe will be repeated until we reach the stropping stage. The one change in angle that has being profiled with the metal file now comes into its own. This one change in angle means that we have less to think about when sharpening and is easier to maintain. To find this angle for sharpening simply place the knife flat on the stone and then rock it forward until the cutting bevel is sitting flush.

 
Knife blade lying flush with sharpening stone before cutting edge is found 

Knife blade tilted forward to find cutting edge on the sharpening surface

To maintain an even and balanced edge to the knife we are going sharpen each section of the blade on both sides evenly, 10 seconds is a good time. This means we do not have to attempt to sharpen the entire length of one side of the knife which requires a degree of accuracy and which will be difficult to maintain for long periods. Instead we will break the sharpening down into three sections along the blade and sharpen each side of these in turn, bevel close to the handle, along the belly of the knife and the tip.

 

Sharpening being broken up into sections; here focusing on the blade closest to the handle

Sharpening the mid-section and belly of the knife

Finally sharpening the tip

Once happy with this process repeat through a series of progressively finer sharpening blocks/stones until you have reached an edge that can remove shavings of thumb nail at 90⁰. If your knife does this it is already very sharp and will perform almost any task well. That being said if you remember back to earlier when the process of sharpening was described under the analogy of saw teeth then your sharp knife still has a row of fine saw teeth right the way along it. We now need to remove these teeth so that you have a longer lasting edge to your knife.

The process of stropping is extremely similar to that of sharpening but with a few key differences. Where with sharpening a knife we apply a ‘cutting’ action across the sharpening stones in order to gain an edge, with stropping this would obviously lead to us cutting the leather in to multiple pieces. To strop our knife we pull it back across the leather maintaining the same angle that we did whilst sharpening, always maintaining that one change of angle. What the textured side of the leather is now doing is rocking the microscopic saw teeth generated through sharpening back and forth until they cleaning snap off and leave us with a cutting edge that is much more robust in use. This is good news all round as it results in the knife performing better and means we shouldn’t have to sharpen it quite so often. The secret around this is to sharpen and strop regularly after use so that it should be a simple two minute job. Paying attention to your knife after weeks of heavy use will mean that a whole evening in the kitchen getting your knife back into working condition is needed. As a guideline to how long you will need to strop for, aim for at least twice as long as you’ve spent sharpening. This can quickly add up to a considerable amount of time if you let your knife get blunt and so is another argument for regular maintenance!

Process of stropping being illustrated

Hopefully now you have a fully handled and fully sharpened knife that is ready for use throughout your future projects. What I intend to cover in the final installment of these blogs is how to make a woven bark sheath that will allow you to carry the knife safely but also in a beautiful fashion on all your bushcrafting forays!

 

Danny Hodgson

Woodland Ways Instructor

 

References:

–          I just want to say thank you to Ben Orford for his advice and guidance throughout this process. He has offered some superb knowledge on how to complete the knife making process.

–          A note to Mora knives of Sweden should also be made as I have used their knives now for many years now and their products have been a valuable source of design inspiration.