Using Profile Scrapers
Kelton curved neck scraper with handle
Profile Scrapers Overview: One of the more common turning tools in a woodturners toolbox are scrapers. Most of us own the usual compliment of straight and round (bull-nose) nose scrapers and perhaps a left/right skewed scraper. While traditional scrapers like these are commonly used by woodturners, few own or use contoured scrapers.
Profile scrapers are specially shaped and ground scrapers that are designed for specific cutting tasks, like creating back cuts (an under cut on the inside of a bowl or other form) on bowls and platters, or working on the shoulder area on hollow forms. While there are many different ways to accomplish almost every task in woodturning, using profile scrapers is at times, an easy and fast way to get the job done.
An Undeserved Reputation
Various Kel McNaughton curved profile scrapers
Scrapers have a bad reputation with many woodturners. I've heard many horror stories through the years of turnings that were ruined, or damaged by the use of a scraper. I've also heard turners say that scrapers are an "Ill wind that blows no good" and only tear the grain, making the surface worse than when you started. Still others say that cutting is always better than scraping, so why scrape at all?
The fact is that scrapers have a bad reputation for sure, but it is largely undeserved. Using any tool improperly can result in torn grain, or surface damage. When used properly and with a fresh edge, scrapers are as useful as any other tool in your inventory. When used in a shear scraping mode (with the cutting edge held at a sheer angle of approximately 45 to 55 degrees), scrapers can leave the wood surface smooth enough to start sanding at 320-grit, substantially reducing your abrasive protocol.
For additional information on using shear scrapers, click here.
On dense exotic hardwoods like Violet Rosewood for example, scrapers can actually produce a better surface off the tool than a gouge -- an undeserved reputation indeed! However when used improperly, a scraper can be your worst nightmare. It can tear and mangle end grain fibers and even produce peck out on the surface of the wood. Most of the problems I see with my students when using scrapers centres on not keeping the edge sharp enough, or improper presentation of the tool on the surface of the wood. Luckily, both of these problems are easily remedied.
Why Profile Scrapers
Two different ball-end profile scrapers from Kelton Tools
Profile scrapers offer a much easier way to produce certain finishing cuts like back cuts on rims, or relief cuts under the shoulder of a hollow form. Regular scrapers like flat, round-nose, or left and right skewed scrapers are usually too large to do any tight quarters work. Even if a traditional scraper can fit inside the opening on a project, it may not have the right profile shape for intricate profiling operations.
In addition, regular scrapers usually feature a large sharpened surface, which may make the cut too aggressive on thin walled projects, whereas profiled scrapers typically present a much smaller sharpened edge to the wood, allowing light cuts to be taken with ease. Also, the unique shapes of some profile scrapers allow for easy access in difficult to reach areas, where a regular scraper could never reach.
Types of Profile Scrapers
Large and small skewed end profile scrapers from Kelton Tools
There are many different types and sizes of profile scrapers available including numerous curved and bent shapes, ball-end, ball on post, left skewed, teardrop, square, straight-end and pointed. If you need a custom profile shape that is not available, you can easily take an unused straight edge scraper and grind the exact profile you need using a bench grinder. Final shaping can be completed with shaped abrasive cutters mounted in a hand held rotary tool.
Using Profile Scrapers
Upper: Henry Taylor Tools profile scraper;
lower 3: Kelton Tools micro profile scrapers
Most wood surfaces can be improved if the scraper is held at a sheer angle of 45 to 55 degrees in use, instead of laying the scraper flat down on the tool rest. Depending on the specific shape of the scraper and the clearance around the tool, this presentation may not be possible. If the scraper must be used flat on the tool rest, raising the handle slightly so the end of the handle is higher than the sharpened edge is preferable over a flat presentation of the cutting edge to the wood.
To see two short video segments on shear scraping the outside and inside of a bowl, click here.
The Importance Of Frequent Sharpening
The number one problem I see with my students when using a scraper is not sharpening the edge frequently enough. Scrapers that are used straight off the grind stone (no honing) feature a tiny burr on the cutting edge that does the cutting. This tiny burr does not last very long and must be refreshed frequently during use.
Just like any other cutting edge, as the edge begins to wear, the quality of the cut degrades. If you're using a scraper with a dull edge, chances are very good that you will experience torn grain or other surface damage. By keeping this edge frequently sharpened, you substantially reduce the chances of compromising the surface quality of the cut.
How often should you resharpen the edge? That depends on the quality of the steel in the scraper and the type of wood you're turning. As a rule when working with a typical M2 HSS scraper, I refresh the edge after every 25 – 30 seconds. Yes, you read that right, every 25 to 30 seconds! Scrapers work best with a freshly sharpened edge. If you get in the habit of refreshing the edge every few seconds of use, the quality of your cut will be dramatically improved.
If you're using a scraper made from one of the longer wearing exotic steels like powder metal steel or cryogenically treated steel, you can get a little more life from the edge. If I'm using a cryogenically treated M2 HSS, or a powder metal scraper, I typically refresh the edge after every 45 to 50 seconds.
For additional information on cryogenically treated turning tools, click here.
To Hone Or Not To Hone
I usually use scrapers with the burr intact (straight off the wheel, no honing), unless I'm working with a very dense exotic timber. In these cases, I use a fine credit card size diamond hone to remove the burr completely before use. To remove the burr, simply lay a diamond hone flat on the top of the scraper and lightly rotate the hone over the sharpened edge in a circle. It only takes a few seconds to remove the burr.
Remember if the burr is left intact, the cutting edge will be more aggressive. If the burr is honed away, the cutting edge will be less aggressive. If your scraper is somewhat grabby in use and you're using a freshly sharpened edge, with the tool held in the correct cutting position and you're working with a dense hardwood, try honing the burr off and see if that makes the cut more controllable. With some timbers, having no burr at all is just what the doctor ordered.
Experiment a bit with leaving the burr on and taking it off. There is no real hard and fast rule here regarding the burr, since the timber you are working with at the moment, as well as the thickness of the walls on your project, both tend to influence your decision.
Safety Note: Always follow all manufacturers safety instructions before working with your lathe, or any of the tools or products you may use. If you are unsure about any operation, obtain competent professional instruction before proceeding. Use and wear all necessary safety devices during turning and observe safe woodturning practices to prevent accident or injury.
|Steven D. Russell is a professional studio woodturner, teacher and writer. He has written numerous articles for international woodturning magazines, which have been published in more than 78 countries around the world. Steve has demonstrated in numerous cities across the United States. His studio, Eurowood Werks, specializes in bowls, platters and hollow forms with unique visual and tactile treatments. |
Steve is also a regular featured writer for the Guild of Master Craftsman's "Woodturning" magazine, published in London England. Woodturning magazine is the world's leading magazine for woodturners. Look for his monthly articles covering technical topics, or project based articles in each issue.
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