Turning a New Burr on a Scraper
In the sharpening class, he also taught how to sharpen and use a scraping card, using a burnisher, flat file, and 1000 / 2500 sandpaper. He had people bring new scraper cards to class, remove the bur, and pull a new one. I forgot to bring mine, so I asked him for the class card (he has a box of them for use in other classes) that needed the most work.
Burnishing tool, flat file (flat side of medium hald-found, or a flat bastard file), strips of 1000 and 2500 sandpaper, flat surface (ideal is 320 grid paper glued to a sheet of 1/4” glass; the 320 grit is not used other than to keep the 1000 and 2000 paper from slipping during use).
For safety, consider wearing some tough gloves. It’s easy to run a corner or edge on the skin of your hands and give yourself a good cut.
Boraxo soap for cleanup. Tuning a scraping card is dirty work.
Clean the Scraper
If the scraper has any noticeable amount of oil or grease on it, wipe it clean with denatured alcohol.
Removing the Existing Burr
Lay the card flat. Use a burnishing tool, placed flat on the card and perpendicular to the edge, moving it back and forth a few times to flatten the bur.
Flattening the edge
Put the card in a vise that has wood pieces over the jaws, fairly tight. Use a flat file (such as a bastard file) to file the edge. Carefully hold the file perpendicular to the edge, while orienting it so that you get as much contact between the abrasive part and the edge as possible (not quite parallel). When filing, you can tell when the rough, uneven parts become smooth; stop when the resistance is even.
Sanding the Faces
To remove any burr from flattening, and to smooth the face, rub each side on 1000 paper strips on the glass plate a few times. Best is to do a little more than half of the face, holding the card with your fingers, the long way, then turn 180 degrees to do the same to the other side. Now turn the card over and repeat for the other side.
Reburnishing the Square Edge
Put the card back into the vise. Using the burnishing tool, held perpendicular to the face, press and rub about four passes (each stroke, up, or back, counts as one). Be careful of your fingers near the corner.
At this point you should have a card that is smooth and has no burs. The long end should be square, ready to turn a bur.
Turning the Burr
Now tilt the burnishing tool up to 15 degrees (low for gentle scraping, 15 is aggressive scraping) off of perpendicular on one side. Starting just below the corner, and applying pressure from the burnishing tool onto the edge, pull the burnishing tool along the length with even pressure. Repeat 2 or 3 times. Check the burr by using your nail, pulling gently up to feel it. There should be an even burr the full length.
Tilt the burnishing tool in the opposite direction and repeat for the other square edge. Now take the card out of the vise, turn 180 degrees, back in the vise, and repeat for the other two edges.
The ideal burr gives a consistent amount of scraping over the length of the scraper. If you didn’t get it right, you can always start over from the beginning. Burnishing too many times will weaken the burr and eventually make it fall off.
You’ll notice a lot of fine black powder around. This would be a good time to clean it up, then wash it out of your hands with Boraxo or lava soap.
This is the last entry discussing what I learned in Dan Paret’s class on sharpening.
-- Mark, hack amateur woodworker, Medford (greater Boston) MA