I Was Wrong About Sharpening! Here's 1 Odd Trick I've Been Hiding..

You may have seen these videos on YouTube. A craftsman takes their knife, places the blade at a shallow angle on the edge of the table, then they take a fine metal file and give each side of the edge a few swipes.

Then they begin to cut through skins like a hot knife through butter!

Have I missed something? Or do we worry about having a pristine polished edge too much? Do we even need it on a cutting knife? This blog post will answer these questions.

Now, I've been trialing this method for over half a year now, and today I want to share my experiences, and how I've also improved this method considerably. So read on.

For many of us, we bring out the sharpening stones, or diamond plates to touch up our craft knives when dull. We then begin stropping with polishing compound to create a beautiful smooth edges that pop hairs like a new lawn mower on fresh grass.

A process that can take a few minutes or even much longer.

Sure, after doing this we are left with a mirror polished edge that will cut through anything (for a while), but it does break concentration and takes our focus away from our workflow.

The image shows a smooth polished edge on a small skiving knife

However, regardless of what super magical steel we are using, leather craft knives with a razor edge dull pretty quick. Those who disagree are likely using more force as the knife begins to dull, usually without realising it. It's a process that can happen so slowly it escapes the awareness of many. Only when sharpened do you realise the difference.

For example, I was in a store once buying a pocket knife. The knife I was interested in was also owned by the sales assistant behind the counter. 'I use this knife daily to open boxes and packages, never sharpened it once in over ten years!' he told me. He then handed it over and I felt the edge. I could have safely massaged my face with that knife it was so dull.

Anyway, yes, leather is mildly abrasive to blades, but usually it’s dirt, grit and debris stuck to your cutting surface that really strips the edge off your blade.

This can be from abrasive particles shed from sanding your leather edges, dirt attracted to adhesives left on the surface, even small metal particles from sharpening other knives.

Ok, stropping with polishing compound will sometimes save your blade from becoming dull if done frequently between cuts. But all it takes is your blade contacting a particle of grit to render stropping ineffective, then back to the stones you go.

The file sharpening method I touched upon in the beginning is often seen by leatherworkers and shoemakers from Italy and France. In the uk, a block of wood with loose sandpaper is commonly seen with clicker knives, but the outcome is the same - a toothy edge.

So, what is a toothy edge you ask? Any why is it better in most cases?

A toothy blade is simply and edge with micro serrations. They are hard to see with the naked eye, as these ‘teeth’ are almost microscopic. 

Each tooth has a pointy tip that offers the leather a smaller surface area, this allows it to ‘bite’ and sink into the leather more aggressively than a polished blade.

These micro serrations last longer and are incredibly quick quick to touch up.

Note the jagged tiny serrations on the cutting edge

As is the case with many things, a toothy edge is a compromise. It takes mere seconds to sharpen the edge, and it cuts incredibly well, however it does create more drag, making it slightly tougher to pull through leather.

This is mostly because the blade isn't slick and smooth, it also bites into the cutting surface too.

There are also limitations with a toothy edge, an example would be skiving knives, French edgers, round knives and even grooving tools. These often require a ‘push’ cut. This is where the blade is pushed forward directly into the leather to cut.

So, this means toothy edges require the blade to be drawn across the leather to perform best, or in other words ‘sliced’.

If you try and push a toothy edge directly forward into leather, it will act like a blunt blade, requiring considerable force (see the video demo below). Not good for your fingers, or the leather.

As an example, take a serrated kitchen knife. These knives also have a form of a toothy edge. Same principal, just bigger. If you take a tomato and draw a serrated knife across the skin, it generally cuts into the tomato quite easily, even if the blade hasn't been sharpened in years. 

However, try pushing that same serrated blade directly down into the tomato (a push cut) without pulling back and forth, and you’ll end up with a squashed tomato. Even if the serrated knife is sharp and brand new!

So, in short, a toothy edge cuts aggressively and lasts a long time, but it sucks unless you are slicing the blade across your leather.

Now, commonly the file sharpening method is carried out with soft carbon steel blades. Large clock springs are a common source of material as it's soft and files easily. This makes for a blade with low edge retention (dulls more quickly), but sharpens with only a couple swipes. A good compromise.

However, I don't like compromise, I like to have my cake and eat it too.

Most of us leather crafters prefer to use harder steels for good reason, this increases edge retention considerably, making the blade last longer between sharpening breaks.

However, hard steels really don’t file well, and some blades can be even harder than the file itself! Rendering the file method useless.

So with experimentation, I have come up with a solution to get the best of both worlds. A hard knife steel - with a toothy edge.

I start with High Speed Steel, which I obtain from a hacksaw blade. I then sharpen it with a diamond hand file. Nothing expensive, just a small cheap flat file of unknown grit (I estimate around 600 to 1000 grit). 

I keep the blade in contact with the edge of the table at a shallow angle, then I push the file across the blade moving the file in one direction away from the edge. Then I flip it over and do the same thing on the other side, but this time moving the file TOWARDS the edge. This removes any burr that may have formed from the first step.

I do 5 to 10 swipes on each side. Any more is guaranteed build up a burr that must be removed before the blade will cut. A burr is a microscopic curl or wave that develops on a knife edge after enough sharpening on one side. 

If I am working on thin skins that will stretch as I cut, as an extra step I will take the blade to the strop for about 10 swipes aside. This won’t polish away the micro serrations, rather it polishes the 'teeth' which reduces friction and makes the blade sink into the leather even more aggressively.

You can touch up your toothy edge on the strop for quite some time before you need to go back to the diamond file. Maybe even a dozen times unless you have really dulled the edge somehow.

After trialing this method for the last 6-8 months, I can finally say, for me at least, this is the preferred method for sharpening a leather craft knife. The speed of sharpening, the ability to maintain a curved edge (if you use such a knife) and the extra longevity given by a toothy blade has me convinced.

So, now you know how it’s done, why not give it a try? You may not be convinced, or it could end up being a game changer! It only takes a few seconds to try it.

Just note, some files and abrasives can be too coarse, this makes the blade too rough to be useful. Experimentation with files or sandpaper is key to finding the sweet spot. Trust me, you'll know it when you get there!

If you had success with this method, or you have some other tips and tricks to share, comment below!

Thank you for reading. Philip