Scrapers - Canadian Woodworking Magazine

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Scrapers



Card scrapers, burnisher and file (above)Illustrations by Mike Del Rizzo

A card scraper is the kind of tool that doesn’t make a lot of sense at first glance. You’ll probably read about them several times but ignore them. After all, sandpaper works well and takes little skill to use. And when sandpaper gets dull, you just throw it away and grab a new “sharp” sheet.

However, soon after learning how to use a scraper you'll appreciate its benefits. It will create shavings instead of sawdust, removing far more material in a shorter span of time. For me, it’s a great tool for quick smoothing of problem areas and it’s also handy for removing small areas of finish missed by a chemical stripper.

How Does it Work?
A card scraper is a thin piece of hard steel that can cut small wood shavings using a sharp corner. Even with no burr at all, a scraper will cut using just the sharp, 90° corner. Forming a tiny burr along the edge of the scraper using a tool called a burnisher, makes the scraper even more aggressive, effectively turning it into a tiny hand plane.

If you look at the illustrations, you’ll see a burnisher in use on the edge of a scraper. The burnisher is simply a hardened steel rod that is drawn at a slight angle across the edge to create a burr. If the edge starts at a crisp 90°, then the burnisher will distort the edge into a rounded shape, folding the metal into a tiny hook with a sharp point. Secure the scraper in a vise and hold the burnisher at about 5° to 15° from horizontal. A few strokes with the burnisher will create a hook capable of cutting shavings.


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Filing the edge 

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Holding the scraper

Why Use a Scraper?
While a scraper is capable of completely replacing sandpaper and preparing wood for final finishing, I think you’ll find that sandpaper is still going to be your main finish preparation tool. A scraper must be re-sharpened (or “re-burred”) often. Also, tiny nicks in the cutting edge, which are easily created while cutting through pin knots or other dense areas, will leave trails of fine lines on the surface. This is similar to the long stripes left behind by nicked jointer or planer knives.

For me, the beauty of a scraper is its ability to remove material much faster than sandpaper. For example, have you ever noticed how long it takes to remove pencil marks with sandpaper? Three or four strokes with a scraper will do more work than several minutes of hand sanding.

A scraper is also useful for removing minor tear-out. By bending the scraper with your thumbs, you create a curved cutting surface that can focus on a small area of tear-out. You should also scrape shavings from a larger area surrounding the tear-out so as not to create a noticeable dip in the wood. If you create a much larger concave area and your finish is not super glossy, then your eye won’t notice the slight hollow.

You can also use scrapers to remove other problems such as very distinct mill marks. This can happen when you run your boards too quickly through your milling machines, such as jointers, planers and routers. But it can also happen on a jointer, for example, if you didn’t have enough downward pressure close to the cutterhead, causing the board to vibrate up and down as it passed over the knives.


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Shavings 

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Scraping plane and hand scraper

Some Pitfalls
There are a few common reasons hobbyists fail to master the technique of burnishing a scraper:

1)   Most scrapers don’t have flat sides when purchased. Rub them on their sides on a flat waterstone and you’ll see an irregular dull gray pattern. Continue rubbing the scraper on its side until the gray pattern is continuous, near and up to the cutting tip. Only then will you achieve a crisp 90° corner every time you reburnish a dull scraper.

2)   When a scraper gets dull, you can’t just reburnish it. You need to restore a crisp edge before a burnisher can create a new burr. Start by jointing the edge flat with a mill file, holding the scraper in a vise and holding the file steady at approximately 90°. Push the file across the top edge until it appears wider and flatter, removing the curvature created by the last burnishing.

3)   In addition to using the file, which is called “jointing the edge”, you need to remove any old, dull burrs still felt on the sides of the scraper. Lay the scraper flat on your waterstone, pushing the leading edge away from you. Don’t pull the tool or you’ll fold the burr back onto the edge. A medium grit stone such as 800 or 1000 grit will do. Stop only when you feel no burr left anywhere.

4)   Reburnish using a fairly mild angle. Use enough pressure to create a burr you can feel, but don’t overdo it. Pushing too hard can fold the burr over too far, making the effective cutting angle too steep. Holding the burnisher at too high an angle will fold the burr over so far that it doesn’t come in contact with the wood at a convenient angle.
 
No Going Back
Once you learn to sharpen and use a card scraper, you’ll reach for it more often and wonder what you ever did without it. Start with regular scrapers in various thicknesses. The thicker the scraper, the heavier the shavings. Then buy some curved ones, including the goose-neck scraper I like to use on shop-made crown mouldings. Soon you’ll gain an interest in scraper planes, which make large scraping jobs on flat surfaces easier by giving you two handles and a flat sole to control the cutting action. Being able to plane wood without the usual tear-out issues involved with regular hand planes will make you a believer in no time.


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HENDRIK VARJU
Hendrik Varju

www.passionforwood.com