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Scrapers are one of the most misunderstood but useful tools in a woodshop. A scraper in its simplest form is simply a piece of hardened steel that has a small hook on its edge that was created by bending the corner with an even harder rod of steel. But this tool is capable of making tear-out free cuts in hardwoods that no plane (no matter what the price or amount of fettling) is able to manage.
But why do scrapers work? No one seems agree on why, though there are some tantalizing clues from some Japanese micrographs.
How should you sharpen them? On this topic there is even more disagreement. During the last two months I’ve compiled a list of 14 techniques for sharpening this rectangle of steel, and none agrees on the details. Should you file the edge straight, at an angle (what angle?), or perpendicular to the edge. Which 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 in true “I have no life” form, I decided to try every one of these techniques and compare the results. I used high-quality scrapers from Lee Valley, Bahco (formerly Sandvick) and Lie-Nielsen. All of the published techniques basically worked and created a tool that makes shavings. Yet some techniques are faster, some are easier for beginners to master and some make a tool that really grabs the work.
And after trying all of these techniques and applying my own training and sharpening experiences to the scraper, I’ve think I’ve found a 15th way to sharpen the tool that doesn’t require a lot of equipment, is faster than any of the other techniques and will result in success the first time you try it.
More experimentation is in order, and I need to see if some other people at work can get the same results as I do. But if the technique does stand up, I think it will make a good article.
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Chris,
Very interesting. I am glad you are considering a metallurgist as a possible next step. I have an uncle who is (was) a metallurgist and I showed him your post (printed out, of course) when I visted him at the home this morning. Sometimes it is hard to understand him, but he seemed genuinely excited about your experiment. For what it’s worth, he kept repeating "It’s the heat, it’s the heat" as he read your post. I am fairly certain that he was referring to your post as he was covered in a blanket at the time. Perhaps temperature is a variable that affects results?
Great blog,
Tom
Dru,
A fair number of methods discuss what you’re calling "kicking," though I’m not convinced it’s necessary. There seems to be a lot of confusion on what is happening when you rub the faces. Some say you’re work-hardening the metal. Other say you are bending the edge back over the edge to prepare the edge for the hook.
Still others say you are "consolidating" the metal. All this conflicting advice is one of the reasons I need to dig a little deeper. The next stop for me is a metallurgist.
Chris
You’ve tried 15 different ways? Wow, gotta hand it to a, you’re must truly love woodworking.Looking forward to the article.