Woodworking Tip of the Day: Tuning a Card Scraper

This is catching the MOAM's attention today….. a ten-dollar rectangle of steel that will out-smooth your random-orbit sander on curly mahogany. That is, if you sharpen it right. Most folks crank a big fat hook on it, get a cloud of dust, decide scrapers are overrated and hang it back on the wall. Here's how to tune a card scraper so it peels shavings off like a good smoothing plane.

Why it matters: A scraper takes tearout out of wild grain that no plane will touch, and it leaves no sanding scratches to show up under varnish later. On a boat that's half the brightwork. WoodenBoat's varnishing guide suggests a cabinet scraper for smoothing big bare-wood surfaces like transoms and cabinsides before the sealer coat, and says to scrape a sag out of a cured buildup coat before you sand. Mahogany and white oak trim with interlocked or reversing grain are exactly where a plane tears out and a scraper doesn't. And it's the best tool going for cured epoxy squeeze-out, drips and runs on a hull. Gougeon's people point out that scraping epoxy, especially green epoxy, keeps it from going airborne the way sanding dust does. The catch is that a scraper is only as good as its hook, and the hook is only as good as the square, polished edge under it.

Materials

• A card scraper. Common stock runs from .016″ to .042″ thick (0.4 to 1 mm). Lee Valley sells .016″ and .024″ for fine finishing and .032″ and .042″ for heavier work and paint. Lie-Nielsen's pair is .020″ (supple, good for short, complex surfaces) and .032″ (stiffer, takes a heavier cut on bigger surfaces). If you only own one, make it something in the .020″ to .032″ range.
• A few drops of light oil for burnishing. Lee Valley's instructions note that a fingertip rubbed behind your ear carries just about the right amount.
• A permanent marker
• A hardwood scrap 1¾″ × 1¾″ × 8″ for a filing block
• Duct tape or fine-line painter's tape, for the epoxy-drip trick below

Tools

• A 10″ single-cut mill file. Bob Van Dyke uses a mill bastard. Christopher Schwarz prefers a finer second-cut or smooth file because a coarse one leaves deep scratches in soft scraper steel.
• Sharpening stones or plates: a 1000 waterstone plus a 4000 to 8000 polishing stone, diamond plates, or wet-or-dry paper on glass from 180 or 320 up to 600
• A burnisher: a hardened, polished steel or carbide rod. Ron Hock (quoted by Schwarz) puts burnishers around Rc 58 to 60. Plain spring-steel scrapers run about Rc 38 to 42 and the premium ones Rc 48 to 53 (Lie-Nielsen's are 49 to 51), so the burnisher always wins. Paul Sellers gets by fine with the back of a chisel or a nail set. If freehand angles give you fits, the Veritas Variable Burnisher dials in anything from 0° to 15°.
• A bench vise
• A flat refrigerator magnet. Matthew Teague sticks one on the scraper as a thumb heat shield, and on a long session your thumbs will thank you.

Steps

1. Make a filing block. This one's Brian Boggs's idea, via Fine Woodworking's Michael Pekovich. Bandsaw a 7″ kerf down the length of that 1¾″ × 8″ hardwood block. Slip the scraper in so its edge stands barely proud of the wood (no more than 1/64″) and clamp the block in the vise. Now the file rides the block and can't go out of square.
2. Joint the edge square. Color the edge with marker. Lay the single-cut mill file flat across the block and take long, full-length push strokes. Files cut on the push. On a used scraper the file will skate over the work-hardened steel at first. Keep going until it cuts steadily and the ink is gone. Do both long edges.
3. Hone the faces and the edge. Faces first. You only need the first ½″ or so next to the edge, not the whole card. Go from a 1000 stone to a 4000 to 8000, or from 180 or 320 paper up to 600. Then hone the edge with the scraper held square against a wood block standing on the stone. Move the scraper, not the block, and wander over the whole stone so you don't wear a groove in it. Alternate face and edge until the filing burr is gone and the corner is crisp and polished. Don't mistake that filing burr for a hook. It'll cut, but it leaves a rough surface and dulls fast.
4. Draw the faces. Lay the scraper flat near the edge of the bench and put a drop of oil on it. Hold the burnisher flat on the face, or tipped a degree or two toward the edge, and take firm strokes along the full length, with the burnisher skewed a bit. Schwarz uses five or six strokes. Paul Sellers bears down hard and takes 20 or 30. Do both faces at each edge. This work-hardens the steel and draws a hair of it out past the edge, so the hook turns easily.
5. Turn the hook. Clamp the scraper upright. Lee Valley leaves about 1½″ above the jaws, and Sellers sets it about ⅛″ above his holder block. Lay the burnisher across the edge, square to the faces, then tip it a few degrees. About 5° is a good place to start, and the sources are all over the map here. Tage Frid held his at 85° to the face, which is 5°. Van Dyke goes 3° to 4°, Pekovich just 1° to 2°, and Teague says anything from 1° to 15° works. Lee Valley says most scraping falls in the 3° to 10° range. Schwarz tried 5°, 7°, 10° and 15° hooks side by side and got excellent shavings from all of them. Take two or three light strokes. Tage Frid put it at about 4 oz of pressure, and Schwarz calls it the pressure you'd use to spread butter on bread. Then tip the burnisher the other way for the second corner. A good hook feels like a tiny lip your fingernail can almost catch.
6. Hold it, flex it, lean it. Fingers on the short ends, thumbs together in the middle of the back about ½″ above the edge, and push just enough to put a slight bow in it. More bow gives a narrower, deeper cut. Lean the top forward in the direction of the push. Schwarz works between about 60° and 65° to the surface. Teague starts beginners around 60° and adjusts until the hook bites. Tage Frid started vertical and tipped it until it bit, at about 70°. The lower your hook angle, the more upright you can stand the scraper. Push to chase tearout. Pull, with your fingertips behind the edge, to flatten the slight dish a push stroke leaves. Feather your work out around a bad spot so you don't scoop a divot that shows under varnish.
7. Read the chips. Fluffy, curly shavings mean you're sharp. Dust means you're not. Change your angle first, then check that the hook is still there. Van Dyke figures five to ten minutes of steady scraping before the shavings fall off. Don't push on into dust, because scraping dull rounds over the jointed edge and leaves you nothing to turn a new hook from.
8. Re-turn it before you refile. When the shavings quit, re-draw the faces and re-turn the hook. No filing. Lie-Nielsen says you can usually do that a few times. Teague gets four to six burnishings, and Van Dyke and Tage Frid five or six, before the steel gets work-hardened and brittle. Pekovich says the hook actually lasts longer the second and third time. When it won't take a clean hook anymore, back to the file and start over.

MOAM's shop note: The common mistake is too much pressure and too much angle. You get a big, fragile hook that's hard to control, and Pekovich warns that heavy burnishing can crimp the steel so badly you have to file it off and start over. Go light and stop as soon as you can feel the hook. Pro trick for the boat shop, from Gougeon's Tom Pawlak at Epoxyworks: for a cured epoxy drip about ½″ wide, tape off the scraper's edge everywhere but the center inch. Lean it forward and push along the drip with the blade square to it. Each pass peels a ribbon, and the tape stops the cut right at the fair surface, leaving the drip only a few thousandths proud. Knock that down with a small hard block and wet-or-dry paper. No sanding swirls on your topsides and no epoxy dust in the air. Here in Marblehead we call that a fair trade.

Sources: Bob Van Dyke, "Learn a fast, reliable way to sharpen a card scraper," Matthew Teague, "Mastering the card scraper," and Michael Pekovich, "The right way to sharpen your scraper" (Fine Woodworking); Tage Frid, "The Scraper" (Fine Woodworking #6); Christopher Schwarz, "A Better Way to Sharpen Scrapers" (Popular Woodworking); Lie-Nielsen Toolworks hand scraper instructions; Lee Valley/Veritas Variable Burnisher instructions and scraper specs; Paul Sellers; Tom Pawlak, "Scrapers: Versatile Tools for Working with Epoxy" (Epoxyworks/WEST SYSTEM); Matthew P. Murphy, "Varnishing Basics" (WoodenBoat); Chesapeake Light Craft, "Cabinet Scrapers for Boatbuilding."

MOAM Out.