A Better Way to Sharpen Scrapers
Scrapers are one of the most misunderstood but useful tools in a woodshop. A scraper in its basic form is simply a piece of hardened steel with a small hook that is created by pressing on the tool’s edge with an even harder rod of steel. This tool is capable of making tear-out free cuts in hardwoods that no plane can manage.
But how to sharpen a scraper is a mysterious or confusing process for many woodworkers. One reason for the confusion is that there are many different published techniques out there, many of them offering conflicting advice.
So I compiled a list of 14 different techniques for sharpening this rectangle of steel that have been published since 1875. All of the 14 techniques basically agree that there are three steps to sharpening a scraper: Filing the edge of the tool, removing the file marks with a sharpening stone and then creating the hook (sometimes called the burr) with a hardened rod of steel, usually called a burnisher.
But none of the accounts agree on the details. Should you file the edge of the scraper with the file parallel to the edge or at an angle (and if so, what angle)? What kind of file should you use? Should you stone both the edge and faces of the tool? To what grit? And how should this be done?
Do you have to burnish the faces of the tool before turning the burr of the scraper? If you do, what angle do you use? And how should you burnish the edge to create the hook? At what angle? Do you slide the burnisher along the edge as you turn the burr?
So one weekend I tried all these techniques then compared the results. I used high-quality scrapers from Lee Valley, Bahco (formerly Sandvik) and Lie-Nielsen. All of the published techniques basically worked and created a tool that made shavings. Yet some techniques were faster, some required fewer hand skills to master and some made a hook that really grabbed the work.
After trying these techniques, applying my own training and talking to an expert on steel tooling, I think I’ve found a 15th way to sharpen the tool that doesn’t require a lot of equipment, and is fast and is easy for beginners.
Like Any Tool’s Edge
What’s important to understand is that a scraper is like any cutting tool and it responds to your sharpening efforts in the same, predictable way.
A sharp edge is the intersection of two steel surfaces (in a chisel, it’s the bevel and the face, which is sometimes called the back of the tool). Any cutting edge is at its sharpest when these two surfaces meet at the smallest point possible.
The edge becomes more durable as it gets more polished by higher grits. Polishing removes tiny scratches in the steel, and scratches are the places where the edge begins to break down and become dull.
A harder steel can also contribute to a more long-lasting edge. However, if it is too hard it can be fragile and susceptible to shock.
All these rules apply to scrapers. The cutting edge of a scraper is two surfaces: the edge and the face. The more polished those two surfaces are, the more durable and sharp the edge is. So with that principle in mind, here’s the thinking behind my scraper-sharpening technique.
Step 1: File the Edge
The edge of the card scraper should be filed square to the tool’s faces (all the sources agree on this). You should use a fine file. Look for one with single rows of parallel teeth (this is called a single-cut file) and teeth that are fine, usually labeled “second cut” or “smooth.” Scrapers are soft and easy to file, so a coarse file will create deep scratches that are difficult to remove.
Color the edge of the tool with a permanent marker. This will allow you to see where you are cutting. When the color is gone, the filing is done.
How you hold the file in use is in dispute. You can work with the file parallel to the edge, perpendicular to the edge or anywhere in between. All can result in a square edge, but there is only one technique that gives perfect results every time regardless of your skill with filing: Use a jig, either commercial or shopmade.
Veritas makes an inexpensive jig that I like. You also can purchase a vintage saw jointer, which was used to file handsaw teeth down for reshaping. Or you can cut a kerf in a block of wood to hold your file. Freehand filing is great if you are skilled at it. Most of us are not, so I recommend a jig.
Step 2: Stone the Tool
After filing, you smooth away those scratches with a sharpening stone or two. Some sources say you have to stone only the narrow edge of the scraper. Others say you stone both the edge and the faces. Because we now know that a good edge is the intersection of two polished surfaces, you should stone both the edge and face.
How do you stone the edge? You can rub the tool on edge on your stone, but this can make it difficult to balance the tool. Some published accounts recommend sandwiching the scraper between two blocks of wood for additional support, but you’ll usually end up abrading the wooden blocks more than the tool.
Alternately, you can bow the scraper as you rub it on the stone to spread the edge out over more of the surface. This works well with flexible scrapers but is quite difficult with the thicker ones.
Instead, I like to hone the edge of the scraper on the sharpening stone with a single block of wood supporting it from the side. I’ll sharpen on the face of the stone as shown at right. This is foolproof and allows you to spread the wear out across the stone’s face by moving the block of wood.
With the edge stoned, how do you stone the two faces of the tool? Here is where the real trickery begins. Every other technique that discusses this has you rub the face of the tool to and fro on the stone. This works, but it takes a while. The face of a scraper is a lot of steel to deal with. Most woodworkers do what they can on the faces and give up when they get bored. And that doesn’t cut it.
Why sharpen a bunch of steel you aren’t using? So I took a page from the playbook of David Charlesworth, a British craftsman. He sharpens the unbeveled face of a plane iron by propping up the back of the tool on a thin ruler set on the stone. This technique, called the ruler trick, sharpens only the section of steel up by the cutting edge.
Would this work with card scrapers, I wondered? It does. And brilliantly. You sharpen only the metal up by the edge. It takes far fewer strokes. And the slight change in edge geometry has no discernible effect on the final cutting edge. Thanks David.
The other question is what grit of stones you should use. This is honestly up to you. The more polished the edge, the more durable it will be in use.