I recently taught a weekend workshop for beginners, and quickly realized that the terms "cutting," "scraping" and "shear scraping" were foreign to this group. I must admit, it was quite a few years into my turning career before I knew and understood the difference myself. When should each method be used? For what purpose? Is it all right to mix the three when turning a bowl? Is it ever OK to scrape a spindle-turned form?
Let me begin by saying (or perhaps confessing) that I first learned to turn when I made a pedestal for a table, and I did it totally by scraping. And, I might add, lots of sanding! I moved on to bowls, happily scraping away. And sanding! I became really good at both.
The transition to cutting was awkward, but many bowls and spindles later, after I learned to cut and shear scrape, those methods paid off in saved time. I still utilize scraping ... it has a time and place, but it has taken a backseat.
Scraping
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| For shear scraping, the round-nose scraper is held with the cutting edge slightly angled down, tilted on the toolrest.
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Scraping is done with scrapers: round-nose, square-end, diamond-point, or angled. Scrapers are best when they are heavy, which helps make them more stable. The profile of the end you use depends on the profile of the object you are turning: round-nosed scrapers for concave areas, straight-ended scrapers (of any sort) for convex areas. Scrapers have bevels, but unlike gouges or skews, the bevel of a scraper never touches the wood. The scraping is done at or slightly above the center line of the work to prevent dig-ins.
Scraping is easy to learn: place the tool flat on the tool-rest, hold it horizontal, then slowly advance it into the wood. That's (almost) all there is to it. Like all other tools, scrapers need to be sharp. The bevel should be about 60 degrees or steeper, even as steep as 30 degrees. I've found that scrapers usually come with a bevel too close to 90 degrees. With that type of bevel angle, catches can happen when the bevel digs into the wood. You want a good bit of clearance between the bevel and the wood you are cutting. A note of caution, however: a bevel that is too steep decreases the stability of the edge.
One advantage of using a scraper is to remove minute amounts of wood in specific areas of a turning, especially the inside or outside of a bowl. Say that you've achieved a great cut on the inside of your bowl, from the rim all the way to the center of the inside. But there's just one small area that's a bit higher than the rest, and the bowl is already as thin as you want it to be. It's difficult for most of us to go back and take away that small amount. This is where a scraper is handy. Since you've already achieved a good cut, scraping will leave a clean-cut surface as well as a smooth curve.
Cutting
Cutting is done with gouges and skew chisels. Unlike scraping, it's important to make sure the bevels of these tools are making contact with the wood. Well, sort of making contact. I like to think of this as "acknowledging" the bevel. When you're actually cutting, the bevel is barely, if at all, touching the wood. Beginners generally "ride the bevel" way too much. But that's OK. It's better to do that than to avoid using the cutting method.
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| In this photo, the author uses a skew chisel as a straight-ended scraper to shear scrape the profile of the outside of the bowl. |
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Cutting should be employed as much as possible. It's faster than scraping, not as hard on your body, and it leaves the fibers of the wood in better shape than scraping does when initial cuts are made. For spindle turning, I recommend using the cutting method almost exclusively. It leaves the wood in a condition that requires extremely little sanding. The exception to this would be if your turned object is to be painted. A not-so-smooth surface is required for paint to adhere to the wood, so roughing it up a bit with 120- or 150-grit sandpaper is advised.
The primary thing to know for cutting on spindle turnings is to make the cut downhill: from the high point to the low point for all elements.
For bowls, rough out the initial shape using a large bowl gouge. (Roughing gouges are meant for spindle turning!) On the outside of the bowl, cut in an uphill direction, from the base of the bowl to the rim. On the inside, cut from the rim towards the center. It is possible to cut either uphill or downhill on the inside of a bowl, but in general, uphill will give you a better cut. Cutting with a gouge is done with the flute pointing in the direction of the cut, the tool traveling in that direction, and some portion of the lower half of the cutting edge contacting the wood. Those are the three "rules" of cutting or shear scraping with a gouge.
The steepness of the bevel is of some importance for achieving a good cut and for controlling the tool. A steeper angle, one closer to 30 degrees, will be challenging to control, but it will give you a cleaner cut. A bevel closer to 70 or 80 degrees will be easier to control, especially when working on the bottom of a bowl, but the cut will not be quite as clean.
Adjusting the Bevel for Clearance
If your lathe can only handle bowls of small diameter and your tools have long handles, you will find that the bed of the lathe gets in the way when cutting on the inside of bowls. Here are three solutions: 1) buy a larger capacity lathe; 2) use tools with shorter handles or cut off the extra length from your long-handled tool; 3) grind the angle of your gouge more towards 60 or 70 degrees. That will allow the tool handle to be lifted high enough to clear the bed of the lathe yet still make a cut.
Shear Scraping
Shear scraping can be done with scrapers or with gouges. To shear scrape with a scraper, make sure the cutting edge is sharp and has a slight edge to it. This can be achieved either straight off the grinder or by raising a very slight burr on the cutting edge. Instead of holding the scraper flat on the toolrest and horizontal (as for scraping), lift the handle slightly so the cutting edge of the tool is pointed slightly down. Next, lift the side of the tool and present the cutting edge to the wood at an angle. Take a light cut. Shear scraping is meant to take off only a slight amount.
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| To shear scrape between a bowl and headstock, you can hold the tool with the flute open upward and the tool handle down. Try pulling the tool to cut in difficult areas. |
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To shear scrape with a gouge, the profile of the gouge should be that of a fingernail grind. Present the cutting edge directly to the wood, ignoring the bevel. Place the cutting edge of the tool at a slight angle to the wood. The tool handle will be at a more vertical position than for cutting. Pull the gouge in the direction of the cut. Use a good portion of one side of the tool's cutting edge. Using a long section of the cutting edge helps create a smooth-flowing curve.
The advantage to shear scraping is that you can achieve a very fine cut, especially with difficult-to-turn woods. It's the only way I can get a good cut on cherry, for instance. Also, shear scraping is sometimes the only method for accessing difficult-to-cut areas, especially when turning the outside of a bowl when it's mounted with the opening facing the tailstock. The small clearance between the back of the bowl and the headstock often makes it difficult to remove wood from the back and bottom. Shear scraping not only allows you access, it lets you cut in the direction needed for a cleaner cut.
I realize that word directions are difficult to follow. We are visual people. Study the photos accompanying this article. Practice. If you don't have a catch or dig-in, you're not extending yourself or learning new methods. For safety's sake, always take a light cut and keep your tool-rest as close as possible to the wood. Turn at moderate speeds until you are proficient to keep those catches minimal. And by all means, please keep on turning, and have fun!