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How To Use A Scraper Burnisher

How To Use A Scraper Burnisher


Over the decades, we have taught countless woodworkers the amazing value of the simple card scraper. As with most blades though they are almost worthless unless sharp, and when it comes to card scrapers this is particularly so. Card scrapers may have the highest bang for buck ratio of any tool, but they dull quickly, within about 10 minutes of use.



The good news is scrapers are among the easiest of all tools to resharpen if you do it right. So make it easy on yourself, get the right information and the right tools for the job. In this article we zero in on the mysterious burnisher, but you can learn everything you need to know about sharpening a card scraper and burnishing techniques from our complete article on the subject How To Sharpen A Card Scraper.

We have had folks ask if they can use all kind of things as burnishers...axle parts, engine wrist pins; screwdrivers seem to be the favorite grab. Under the right circumstances any of these could work for burnishing, but why not get the best tool for the job? There is a wide range of burnishing tools on our site that can actually speed the task along and many of them are nice tools to have and appreciate to boot. A good burnisher needs to be two things to get the job done:

  • Much harder than the tool it is burnishing (the steel of most card scrapers can range between Rc38-55).
  • Highly polished with a completely smooth surface.
The burnishing process will turn a fine burr off the edge of the scraper by rubbing it with a harder piece of metal. The burr serves as a tiny, high-angle cutting edge, with the body of the scraper acting as a chipbreaker. Properly burnished, the card scraper removes fine shavings from even the hardest wood, offering the quality of a planed finish. Scrapers are great to use on woods whose grain characteristics do not allow for conventional planing.


HOW TO USE A BURNISHER

Burnishing

Burnishing is the final phase of prepping a card scraper. Once you have sharpened the scrapers edge it is time for burnishing. A burnisher is a short rod of very hard steel polished to a very smooth surface. To "burnish" is "to polish; make shiny or lustrous by rubbing". The burnisher will finish the job of sharpening the scraper's edges and then gently shape them into high-angle cutters. Lay the scraper on a firm, flat surface such as your bench, and wipe a liberal smear of heavy oil along the edge. Use 20 or 30 weight motor oil or the like, not thin cutting oil; you want to lubricate the scraper to be sure the burnisher slides smoothy with no chance of biting into it and tearing the cutting edges. Bring the burnisher on flat, with your thumb bearing down hard directly above the scraper's edge, and stroke its full length fifteen or twenty times. This will make the surface smoother (hence sharper), and both harder and tougher as well, so the tiny burr you're soon to create will be able to stand up to the kind of hard work you're going to ask of it. Apply eight to ten pounds' pressure; enough to feel firm without hurting your thumb. Flip the scraper over and burnish the opposite side, then turn it around lengthwise and do the other two edges as well.

Turning The Burr

We might be smarter to call this "forming the edge" to avoid confusion about what "burr" means. In this case, it does not mean the sort of torn, ragged cornice we're usually talking about when we use the word. On a scraper the "burr" is actually the clean, smooth and continuous cutting edge created by filing and burnishing. You're going to use the burnisher very gently to push that cutting edge up to form a tiny, sharp hook that runs the full length of the scraper. Daub a little more oil along the edge, and hang the scraper 1/2" or so off the edge of your bench. Present the burnisher vertically, then tilt the top inward slightly (about 5°) so it contacts only the scraper's upper edge. The edge you're about to work on is sharp, which means there's very little steel right out at the cutting edge—which means it takes very little pressure to push it up into a tiny burr. Applying no more than about 8 ounces of pressure, stroke the edge full length five to ten times. Now wipe off the oil and feel the results. The burr should hardly be big enough to detect; it should feel mostly just like a very sharp edge. A distinct, heavy burr won't work well at all, so if you've produced such a thing, use the burnisher to lay it out flat and try again. Turn a burr on all four edges, so you'll be able to do plenty of work before you need to start over.

Reburnishing The Tool

Honed and burnished correctly, your scraper can be used, reburnished flat and a new burr burnished for reuse. This process can be repeated several times before it is necessary to refile and hone the edge again.


*Always be mindful of the two most common mistakes when using a burnisher: applying too much pressure and going for too much angle.


Shop for all Scraping Tools - including Burnishers and Card Scrapers

Lee Laird's Take on Preparing A Card Scraper.

Learn More information about How To Sharpening A Card Scraper.

Learn more about the importance of adding Card Scrapers to your tool box!.


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