Lathe Turning Tool: Chisels

I’ll now turn my attention to the second family of turning tools-chisels. Unlike a woodworker’s chisel, which is single beveled, a turner’s chisel is double beveled. The edge is in the center of the blank with a bevel extending to either side (see the bottom illustration above). Although difficult to find, it is still possible to buy a traditional turner’s chisel. A typical chisel is 1 in. to 2 in. wide, about 20 in. long (including the stout handle), and ground with the edge square to the blank (like a woodworker’s chisel) with double flat bevels that meet at approximately a 42 inclusive angle. The chisel is the one tool in a turner’s repertoire that works better with a flat rather than hollow-ground bevel.

You should present a traditional wood turner’s chisel to the wood as shown in the illustration on the facing page. Since the illustration depicts cutting to the left, the chisel is turned slightly toward that direction and only the edge of the tool contacts the rest. A common beginner’s mistake is to try to lay the entire tool flat on the rest before presenting it to the work.

I like to lock my fingers around the right edge of a chisel using a relaxed but firm grip. The real control of this tool comes from twisting it ever so slightly up and down to keep it cutting correctly. A beginner often makes the mistake of trying to raise and lower the handle or swing the handle left and right to control the cut. In the split second the cut gets the least off of the bevel, the edge starts cutting a helix in the work and is drawn down toward the rest with the corner (T) digging in. These catches leave nasty craters in the work. Although I like to think that there are no mistakes, only new design opportunities, chisels catch with such gusto that the work is often ruined.

With that said, it is useful to purposely catch the chisel to learn the dynamics of the process. (This exercise can be done just as well with a skew chisel as with a traditional chisel.) Set the lathe to a very low speed, making sure the work is securely held between centers. If using a skew, make sure your left hand is on your side of the tool rest because skews can pinch the fleshy part of your hand against the rest in a catch. (I typically hold the tool loosely with my left hand in back of the rest.) With your right hand, raise the handle slowly upward to cause a catch-along with a new design opportunity.

How a Chisel Cuts

The bevel we cannot see (the one on the far side of the tool) is rubbing the work and the edge is cutting somewhere between the dotted lines “A” and “8”. The cut should take place in an area to the left of center of the tool (as shown by the shaded area), and no more than half the length of the cutting edge should be engaged. This puts the cut in an area just to the right of the corner of the chisel “H” and somewhere just to the right of center. The other corner of the chisel ‘T is well clear of the cut.

SKEW CHISELS

Historically called long-corner chisels, skew chisels have two advantages over traditional chisels that make them easier to control. First, the handle may be brought at nearly right angles to the work, which allows you to stand directly behind the shank of the tool. Second, a skew also does not have to be tipped to quite as high an angle from where its edge contacts the rest as a traditional chisel does.

Beginners should start with a fairly wide skew that is 1 in. to 1 ½ in. One (among many) of the problems with sets is that the skew is generally in the ½ -in. to 3/4-in. range. Those skews are far too narrow for easy control, even in skilled hands. I have three skews: a 1 ¼ in., a 1 in., and a ½ in. I use the 1 in. 90 percent of the time and only resort to 1 ¼ in. for large architectural work. I use the ½ -in. one, which does not even have a handle, in very tight quarters such as when cleaning up a shoulder next to a bead.

A skew is one of the few turning tools that is generally delivered with the correct bevel angles and grind. However, the rectangular section the chisel is made from is usually achieved by Blanchard grinding, which leaves the corners of the rectangle sharp. Sharp corners do not slide along the tool rest, making the tool unpleasant to use as well as uncomfortable to hold. The illustration at right on the facing page shows what I call a “tuned” skew, where the corners of the rectangle have been given a healthy radius in the grinder then polished smooth.

Although you seldom have to grind a skew to start, you will have to regrind it if the tool has a hollow grind or if it has had dealings with a chuck. It is a simple matter to grind a flat bevel of the correct angle on any bench grinder, but the method will bring a cry from the grinder-safety people. That’s because grinding a flat bevel requires grinding on the side of the wheel even though all modern grinding manuals say to grind only on the periphery of the wheel.

The safety people are worried that an unskilled turner will put excessive side pressure on a thin wheel, causing it to break. They are also worried that the same person might excessively dress the side of the wheel, possibly dressing a groove that could start a general fault in the wheel-a break on the dotted line so to speak. But I have never known an experienced toolmaker who did not grind on the side of a wheel once in a while. In addition, hardware stores sell twist-drill sharpening jigs that only work by using the side of a wheel.

The important thing is to bring some common sense to the situation. An occasional grinding on the side of a wheel is okay if you put only light side pressure on a ½ in. or wider wheel (the wider the better). Never excessively dress the side of a wheel. I typically lightly dress the sides of a wheel with a diamond dresser to true it up when I first mount it, then only dress once or twice more with a diamond during the entire life of the wheel. Always keep the grinding shields properly adjusted, and wear safety glasses or, even better, a face shield with safety glasses.

To grind a skew, set the rest so that it is level, and use this as a place to rest the shank of the tool for support. When grinding on the side of the wheel, there is a tendency for the top half of the tool to be ground less than the bottom, so you’ll need to compensate for this by putting additional pressure on the top half. I typically apply pressure with my thumb against the top half. As you grind, alternate from one bevel to the other until an edge is formed and you have contiguous flat. Start with a 42° angle, then as your skill increases, lengthen both bevels to as long as 26° inclusive. You will have to approximate the correct angle, but you can cut out a 42° angle on cardboard for comparison.

Grinding a skew on the side of a wheel is the only way to obtain a flat bevel. Grinder manufacturers don't recommend this, but it is safe if you use moderate pressure against a wheel that is 'h in. or wider.
Grinding a skew on the side of a wheel is the only way to obtain a flat bevel. Grinder manufacturers don’t recommend this, but it is safe if you use moderate pressure against a wheel that is ‘h in. or wider.

The cutting edge also needs to be honed on whetstones, which you do in the same way as you would sharpen a plane iron. Simply stone both bevels on progressively finer stones until a polish is achieved. It helps to get your hands very close to the edge so that you can feel that the bevel is flat on the stone. A roller-type jig may help, but you will have to align the roller to the skewing angle of the chisel as shown in the illustration above.

Many turners today like to grind their skews to a curved edge. I do not like this grind for several reasons. First, it is more difficult to achieve the curved grind with a flat bevel, which is still necessary if the tool is going to perform well. Second, it is much more difficult to achieve a keen edge with whetstones on the curved edge. Third, the curved edge does not cut up to a shoulder well. Finally, the curved grind tends to exacerbate harmonic chatter on thin spindles.

How much the tool is turned toward the cutting direction is largely a matter of work diameter. You can achieve a better cut by keeping the handle as square to the work as possible, with the understanding that it can almost never be perfectly square (see the illustration on p. 130). You have to sufficiently skew the edge to the centerline to keep the toe clear of the cut. As the work diameter increases, you must increase the skewing angle by turning the tool further left and moving the handle right. At still larger diameters, you have to go to a wider skew because the toe will no longer clear the cut.

Long, thin work is subject to harmonic chatter where the work vibrates between centers, causing a spiral ripple in the finish. The more the edge is skewed to the work, the more harmonic chatter is exacerbated. Therefore, you should keep the handle of the skew as square to the work as possible.

A flat bevel contacts the centerline from the cutting edge to the heel of the bevel. If the edge is hollow-ground, there is no support for the cutting edge between where the heel of the bevel contacts the centerline and where the edge is cutting (which is also on the centerline). Therefore, a flat bevel makes the tool much more stable.

OVAL SKEWS

A rectangular skew chisel is difficult to use because the tool is unbalanced. The center of gravity is not under the downward movements of force because only one edge of the tool can contact the rest. An oval skew changes all of this. It creates a skew with a center of gravity that is nearly under the center of force-a center of gravity that is free to change with the rolling action of the tool.

Unfortunately, most oval skews are delivered with too long a bevel (26°) for most beginners. The problem can be fixed, though, by shortening the bevels to about 42°.

Heel Cuts

To OVERCOME HARMONIC CHATTER, you can use a heel cut. I generally wrap my hands around the work and hold the tool down on the rest with my thumb. I never grip the work so tightly that my hands get the least warm, although my flesh provides a dampening action that greatly reduces harmonic chatter. I think this hold also increases the pressure of the bevel against the work so that the tool effectively acts as its own steady rest. This is also why it is best to use a wide skew. The wider edge puts the toe further out of harm’s way. At some point, only a steady rest will solve harmonic problems (and sometimes not entirely), but the combination of the heel cut and hands cradling the work will often carry the day.

You also need to use a heel cut if you must roll beads with a skew. I think this job is much more safely and effectively accomplished with the spindle gouge, but many seem to feel that rolling beads with a skew is some sort of rite of passage. I encourage you to try it on some scrap. You will find that the trick is using the heel cut and staying exactly on the bevel. Some turners roll beads with the toe, believing this is easier. I do not agree; you are just reversing the heel and toe, and since it is a heel cut that is necessary to roll a bead, the same dynamics apply.

A cutoff tool is easy to grind by eye. Simply touch both bevels to the grinder to achieve a 42° or less point, inclusive. Keep the point centered on the blank, especially on diamond tools.
A cutoff tool is easy to grind by eye. Simply touch both bevels to the grinder to achieve a 42° or less point, inclusive. Keep the point centered on the blank, especially on diamond tools.

CUTOFF TOOLS

The cutoff tool, sometimes called a parting tool, is also in the chisel family. A diamond-shaped cutoff tool is the best variation of the tool, although it also comes in a cheaper rectangular variety. The diamond shape has several advantages. It presents less surface area to rub (thus creating less friction in a deep cutoff); it will still cut if the tool is not perfectly vertical on the tool rest; and it cuts a narrower kerf in faceplate-oriented cutoffs. The chief advantage of the rectangular version is its low cost. Both types are generally sold in widths ranging from 1/16 in. to ¼ in. wide.

Because of the way a cutoff tool is presented, you can hollow-ground it; it is best ground to a long double bevel of 42 or less, inclusive. Although most turners use the tool directly from the grinder, it works better in spindle work if you remove the burr by honing it on a fine stone.

To use a cutoff tool, place it vertically on the tool rest and present it at a high angle with the bevel rubbing and the edge just cutting. Rock it down until the cutting edge ends up at the exact center of the work and a parting is achieved. The tool has to slide forward on the rest as the cutoff progresses to keep the bevel rubbing. In a deep cutoff, it is best to take overlapping cuts to keep the kerf wider than the tool. Presenting the tool this way in face work may result in a catch, so for faceplate cutoffs, present the tool at or slightly above the centerline and push it forward to the center.

CONE SEPARATION TOOLS

The cone separation tool is nothing more than a giant cutoff tool. It is used for cutting away the interior of a bowl to save time and wood. By coning away the center of a bowl, more bowls can be turned from the same blank. I often mount a thick blank and cone three nesting bowls from it.

You use this tool the same way as a cutoff tool in face work, but you will have to make overlapping cuts to keep the kerf considerably wider than the shank of the tool. Keep the belt slack so that if there is a jam due to chip buildup, the lathe will slip rather than break your arm. A cone separation tool should never be used with a gear-driven lathe.

OTHER TYPES OF CHISELS

The bedan and beading-and-parting tool also fit in the chisel family. A bedan is much like a 3h-in.-wide bench chisel. It is essentially a super wide cutoff tool (though it is single beveled) and is used with exactly the same technique. The single bevel is ground to a long bevel, about 25° to 30°, inclusive. Like the parting tool, it can be hollow-ground but must be honed to a razor-sharp edge like the skew. It is handy for sizing tenons.

The beading-and-parting tool is basically a 3/8-in.-wide traditional wood turner’s chisel. It can be used both for sizing tenons and for rolling beads, but for the latter it must have a flat bevel. Like a skew, it must be used with a heel cut when rolling beads, but it may be a bit more controllable than a skew for this task.

Support Us By Sharing

Author: Aliva Tripathy

Taking out time from a housewife life and contributing to AxiBook is a passion for me. I love doing this and gets mind filled with huge satisfaction with thoughtful feedbacks from you all. Do love caring for others and love sharing knowledge more than this.

Leave a Reply

Your email address will not be published. Required fields are marked *

*

code