Scrapers DemystifiedComments (0)
This article is from Issue 36 of Woodcraft Magazine.
Finish faster in 5 steps (or less).
Many woodworkers revere the card scraper as if it possesses magical properties. A dirt cheap tool that can remove glue, smooth knots and gnarly wood, strip paint, or knock down finish nibs without making noise or dust may indeed sound like a woodworker’s Holy Grail. But in truth, there’s no great mystery to harnessing the magic of this humble piece of steel. The only trick is creating the hook-shaped burr. Get it right and your reward is a tool that makes shavings without the risk of tear-out. Get it wrong and you’ll get nothing but dust.
The search for the perfect scraper edge separates woodworkers into three scraper camps: Coarse Burr, Fine Burr, and Burr-free. They’re all right. The edge choice depends on the task at hand. Just as you wouldn’t use a freshly-honed chisel to hack notches in a 2×4, you needn’t waste time burnishing a perfect burr to scrape away hardened glue. By trying the following sequence and testing each edge, you’re likely to find the right edge to match your next job.
A good starter set consists of a thin (0.6 mm) rectangular scraper and a medium thick (0.8 mm) rectangular scraper. Thinner scrapers are easier to flex which provides more scraping finesse. Thicker scrapers are tougher to bow. This makes them likely to dish the surface and more suited for heavier scraping. If you can spare a few extra bucks, buy a gooseneck scraper. You won’t use it as often as the straight-edgers, but for removing machine marks and burns from curves, it will earn its keep.
Here’s what the long edges of your scraper should look like at the end of this 5-step process. The burrs will slice the wood like a miniature plane, but without tear-out. Better edge preparation translates into a smoother finished surface and longer-lasting edge. A coarse burr breaks down quickly, but is easy to refresh.
Step 1: Squaring the edge
Use a fine mill file to establish a square, straight edge. The grooved board keeps the file perpendicular to the scraper’s face. Draw the scraper as shown to avoid dulling the file’s teeth.
Step 3: Honing the face
Remove the burr left from filing and then hone the outermost 1⁄2" of the face. A block (with double-faced tape on the underside) provides even pressure across the face of the steel.
Step 4: Drawing out the burr
Tilt the burnisher and glide it across the scraper’s face a few times to polish the edge and draw the metal outward. The resulting burr is undetectable, but this step makes the next one easier.
Step 5: Turning the hook
Hold the burnisher perpendicular to the scraper’s sides and run it along the edge. Repeat this step two or three times, gradually increasing the burnisher’s angle to about 5°.
Step 1: Squaring the edge
Squaring, or jointing, the edge establishes a square, defect-free edge. The most important part of this step is filing the edge straight and square. I’ve tried various jigs and setups to maintain the proper angle, but this jointing block remains my favorite. To make the jig, groove a board to fit your file. Draw the scraper against the teeth a few times until the filing action is smooth, and the scraper’s edge appears uniformly shiny. (An easy way to check your progress is to run a permanent marker along the edge. When the ink’s gone, you’re done.) Joint both long edges.
While it’s the first step in the five-step prep process, the burr produced from filing is surprisingly suitable for rough scraping. The scraped workpiece won’t be finish-ready, but the resulting marks can be quickly erased with a random-orbit sander and 220-grit sandpaper.
Steps 2 and 3: Honing the edge and face
Honing removes the serrations and burr left from the file. Don’t skip this step. Attempting to draw and turn the unhoned edge produces a ragged burr that’s too weak to be used for more than a few passes.
In theory, scrapers are like chisels and plane blades; the finest edges come from the highest grit stones. However, in practice, I can’t detect an appreciable difference in edge quality beyond what I achieve with my 6000-grit waterstone. I suspect the reason for this "grit-ceiling" is due to the way that the burnisher polishes the edge while drawing the hook.
To hone the edges and faces, I use a pair of homemade guide blocks. The edge-honing block maintains the square filed edge and makes it easier to move the scraper around the stone. The face-honing block provides more consistent pressure than can be achieved with finger pressure alone. (To attach the block to the card, use a strip of double-faced tape.)
Once the edges and faces have been honed, the scraper is ready for delicate work such as smoothing nibs from a finish. For more aggressive cutting and versatility, though, move on to the next steps of drawing and turning the burr.
Step 4: Drawing out the burr
Drawing out the edge further polishes it and work-hardens the metal to make a longer lasting burr. One or two passes should be all it takes; too many strokes can overharden the metal and make a brittle hook, like a paper clip that’s been bent one time too many times.
To draw the edge, wipe away any residual honing grit and then lay the scraper flat on the edge of your bench. Apply a drop of oil to your burnisher, and run it along the length of the scraper’s edge using a light downward pressure. Some woodworkers keep the burnisher flat on the steel. I prefer tilting it a degree or two to concentrate downward pressure on the cutting edge.
Step 5: Turning the hook
Clamp the scraper in a vise so that the edge to be burnished is parallel to the benchtop. Starting with only a few pounds of pressure, hold the burnisher perpendicular to the scraper’s face and scoot it along the edge. Make two or three additional passes, gradually increasing the angle until the burnisher is at about a 5° angle. (Less is more. Compared to 15° hooks, the smaller hooks work as well, but seem to last longer.) If you’ve done your work correctly, you should feel a tiny burr along the entire edge.
Tilt the burnisher in the opposite direction to turn the opposing hook, then rotate the scraper in the vise and hook the remaining two edges. When you’re done, make a few test cuts. If an edge isn’t making shavings, burnish it again using a bit more pressure. Until you get the moves down, one or two edges may need reburnishing.
Two ways to scrape
A scraper can be pushed or pulled. Pushing is more aggressive, but also more apt to dish the surface. Pulling is less aggressive but produces a flatter surface.
“Catching the edge” is the same regardless of hand positioning. Start by holding the tool perpendicular to the work and tilting it until the hook begins to make shavings. The exact angle isn’t important, but I find myself scraping at about a 60° angle.
A scraper can be used in any direction relative to the grain without producing tear-out. When scraping a machine-planed surface, work diagonally to level out mill marks.
Restoring an edge
It’s hard to mistake a scraper in need of sharpening. When the card starts to skip across the wood or produce dust instead of shavings, it’s time to take it back to the burnisher.
If you’re using a carefully prepared edge, you can refresh the burr several times before having to re-file the edges.
To do this, lay the scraper on your bench and run the burnisher diagonally across the face to flatten the old hook then turn a fresh one. You can re-hook an edge four to six times before the metal becomes brittle, requiring you to file a fresh edge.
Using A Curved Scraper
Once you’ve used straightedge scrapers, you can try burnishing a curved scraper. Unlike sanding, scraping is faster and less likely to round over a sharp profile. Honing and hooking a curved edge requires some practice but unlike a rectangular card, you only need to work the portion of the edge that’s needed for the job at hand.
Using a curved scraper is also different than using a straight-edged one. A curved scraper won’t match the exact profile. This means that you’ll need to scrape a profile in overlapping passes, rotating the scraper to fit the adjoining section. I prefer using a curved scraper one-handed, and on the pull stroke. Rotate the scraper so the card fits the curve, tilt until the burr begins to grab, and then pull it towards you.
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