Turning with Sharp Tools - Straight Skews
Last month, we began a new series of tutorials which will be covering the proper sharpening of lathe tools. In the introduction tutorial in that newsletter, we covered the proper ways of identifying dull lathe tools. This month, we're going to explain the proper method for sharpening flat skews. Next month, we will cover radiused skews.
When to Sharpen -
Skews should be sharpened as soon as they begin to produce dust, rather than smooth ribbons of wood while cutting.
Correct Sharpening Angles -
There are two angles which must be maintained on the skew. The first angle is measured across the widest face of the tool, from side to side. The most common angle used here is approximately 20 degrees, as shown in the photo on the left below. The length of the bevel should be one and a half times the thickness of the skew, as shown in the photo at right below. For example: if your skew is 1/2" thick, then the length of your bevel should be approximately 3/4" long.
Grinding Methods for Skews -
Skews can be ground in a number of ways. Let's look at the most common sharpening methods, and how each method can affect the tool's performance.
- Sharpening with a Grinding Wheel
Grinding wheels will produce a slightly concave (hollow ground) surface on each side of a skew, due to the rounded shape of the grinding stone. This concave surface causes two potential problems: the turner may have a more difficult time maintaining contact between the bevel of the tool and the wood being turned, and the cutting point can become dulled more quickly. It is highly recommended that a skew that is sharpened on the grinding wheel be honed afterwards to produce a more flattened surface along the bevel. This can be accomplished with a belt sander, or by using a hand held file, as detailed below.
- Sharpening with a Belt Sander
A belt sander is an excellent alternative to using a grinding wheel for sharpening the skew. A belt sander produces a flat ground surface on each side of the skew, which is ideal when using this tool. The flattened bevel allows the user to more easily keep the tool's bevel in contact with the wood while turning, and will allow the tool to maintain a sharper edge for a longer period of time between sharpenings. Be sure to maintain contact with the cutting edge and heel of the bevel against the sanding belt at all times, and keep the front edge of the skew perpendicular to the direction of travel of the belt to maintain the correct angle between the long point and short point of the tool.
- Hand Sharpening
Most turners prefer to hand sharpen their skews unless they are incorrectly sharpened, or have become damaged (nicked or blunted from using the tool for scraping cuts). Incorrectly sharpened or damaged tools will require more aggressive reshaping, and should be done with a grinder or belt sander. A small diamond file or sharpening stone can be used for this process. Simply maintain contact with the point and heel of the bevel against the stone, and make several light passes on each side. This is typically all that is required to maintain a very sharp edge on a skew.