Academy Notes and Tips
the Shopsmith Woodworking Academy
As a rule, when a brand-new set of lathe chisels arrives in a woodworker's shop, both experienced turners and novices alike can't resist taking a minute, just to look at them. But, while a novice may merely gaze in unfocused wonderment at the unspoiled ash handles and the beauty of the satin sheen on the steel, the old hand peers critically and carefully at the thickness of the steel, the length of the handles, and...the cutting edges of the tools.
Why? Because it's that tiny portion of the chisels that holds the true key to producing happy results in lathe turning. But it isn't merely the sharpness of the edge that dictates the results you achieve...the angle, length and thickness of the bevel is equally important to your success. But which bevel works best?
A Shorter Bevel: Most full-size, standard lathe chisel sets come from the factory with a 45-degree bevel. This provides a lot of steel back-up for the cutting edge. As a result, it's a strong, long-lasting bevel for a utility turning tool that can be used for scraping - a technique that centers a lot of stress on the tool's edge.
A Longer Bevel: Many Master Turners typically prefer a 30-degree to 35-degree bevel for shearing. This longer bevel helps them get a better approach to the workpiece and provides easier control of the cutting tool. Even though the cutting edge isn't as durable (because there's less steel backing-up the edge), it will hold a sharp edge well when it's used for this more subtle kind of work. It is important to note, however, that if you use a tool with a longer bevel to scrape, it will dull quickly. A Bevel Sharpening Gauge is a handy tool for helping you judge the proper angle when grinding and/or honing chisel edges.
Flat Or Hollow Ground?: Although you have a number of choices on how to grind the bevel you want, the bevel on a lathe tool is almost always ground flat. Lathe chisels with hollow ground edges are available for special techniques, but again, a flat bevel is tougher and longer lasting if you're using a scraping technique, like most turners.
Benchstones Or Machine Grinding?: You can use an ordinary benchstone to grind your chisels. To save elbow grease, start with a coarse stone such as silicon-carbide, aluminum-oxide, India or a coarse Oriental waterstone...then switch to a fine grit Arkansas, waterstone or diamond stone for the finishing touches. It may take some effort, but it will also help you avoid overheating the steel and drawing the temper out of the edge.
Machine grinding is another option. There are three ways of doing this with the Shopsmith Woodworking System.
The Disc Sander: The first and perhaps easiest of these is to use the Disc Sander on your Shopsmith MARK V, in conjunction with....
...Shopsmith's Sharpening Guide. This special device mounts easily to your MARK V's Extension Table with two screws. A template is provided for locating the mounting holes. Once mounted, it can be quickly set to grind your chisels to nine different angles for shearing or scraping...from 25-degrees to 65-degrees in 5-degree increments (See Fig 1).