Thursday, March 8, 2007

Cabinet Scrapers, Common Problems and Cures

Cabinet scrapers are one of my favorite tools. Once you get them down, you will do things faster and with a finer finish than you ever expected! Which brings me to the first problem in learning to use them, What to expect? As a self taught craftsman, I slowly learned over years of effort the real potential of the scraper. At first, I made some dust, then some scratches, then some shavings and finally outright carving. As I worked, the mystery of why it worked sometimes and not others gave way to understanding, and as with most things it ends up being pretty simple.
The first rule is to expect shavings, not dusty little ones, big plane shaving type curls. To understand the basics of scrapers, look to Bruce Hoadleys book "Understanding Wood", it is a wealth of good info, but it won't tell you what you're doing wrong. From my trials teaching, I hope to peg a few of the problems you're having.
A major problem is rounding the edge too much to turn a burr. The process of stoning the scraper to a mirror finish on the face and edge and a clean 90 degree angle where they meet is full of potential misteps. As a test, try filing the edge flat and square to the side and then take it directly to the wood. Hold it perpendicular to the surface and gently push forward while leaning it towards the direction of the cut (just a little bit forward, more on this later) It will cut beautifully. It will also leave a lot of telltale scratches that we try to avoid by honing, but at least you can see what a sharp edge will do. If this is a new result to you than you know that you need to work on honing a sharp square edge. Try holding a square edged block of wood next to the scraper as you run it on the stones. And switch between honing the face and the edge. Be critical, look carefully at the edge that you've created. Is it geometrically clean and polished? The edge should already feel sharp and take a small shaving without even turning a burr.
Once you have this edge, the next step is to turn the burr. This is a very likely place for your troubles to continue. I start by work hardening (compressing the metal and hardening it) the edge and pointing the burr. I do this by laying the scraper flat on my bench and running my burnisher (could be a screwdriver handle or anything harder than the scraper) flat along the face. A little oil on the burnisher will help. Now a tiny (and I mean tiny) burr has been formed and is pointing straight up along the edge. Now I hold the scraper in one hand and rub the burnisher (held perpendicular to the face) along the edge. Do this about 3 times and the burr will now point toward the face of the scraper. Now angle the burnisher, slightly and run it along the edge again. What I am getting at is that the burr should be tiny (much stronger and resistant to breaking) and barely angled. Most of the problems I've seen in burr turning are attributed to rolling the burnisher way to far. You don't need to end up at a 30 or 45 degree angle, 5 degrees will do. You'll see why when I talk about using the scraper next posting.

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