Gouges, Part 3
The Basic Cut
A bowl gouge is the tool that every turner should master. One can be used in a variety of ways to do things ranging from roughing out a bowl or truing up a spindle blank to making final finishing cuts on the inside and outside of a variety of pieces. This article explains how it works.
There are enough similarities between a bowl gouge and a spindle gouge that most of what is presented here will apply to the spindle gouge as well. The spindle gouge will probably have a shallower flute, and it may be ground with a slightly longer bevel.
A spindle blank makes a good practice piece even though the logical thing might be to use a bowl. So, mount a blank on the lathe as was suggested for the spindle roughing gouge. Then use your SRG to true up the blank. You will then be set to go.
Note: Turners use a terminology to describe the flute position whose meaning is not at all obvious. This is the reference to the flute being either closed or open. Now what does that mean? Pay attention to this in the following, and hopefully, the meaning will become clear.
How to make the basic cut. Position the tool rest at a height so that, with the handle horizontal, the tip of the tool is level with the rotational axis of the spindle.
Don’t turn the lathe On yet. With the handle horizontal, rotate the tool so that the flute faces horizontally to the right, at the 3 o’clock position. Angle the tool so that the entire bevel makes contact with the wood. In this position, the tool will not cut; this is the neutral position. The flute is closed. At first, this should be your starting position when you go to make a cut.
So what must happen to make it cut? Go back to the starting position, then rotate the tool a very small amount until the flute faces the 2 o’clock position. This small counterclockwise rotation opens the flute a tiny bit and allows a small section of the cutting edge (top wing, near the tip) to engage the wood. Rotate the lathe by hand and you should get a small shaving. Keep the bevel rubbing against the wood while you do this.
A tiny portion of the top wing near the tip is actually cutting the wood fibers along a line parallel to the bevel. Some of the cutting action may occur along the tip of the bottom wing. The fibers then move down onto the inside surface of the bottom wing which lifts them away from the wood. This is a fluid, continuous motion and a shaving is the result.
After you are able to get a shaving, start the lathe and try it for real. Keep the RPM low; about 800 RPM is fast enough at this point.
Place the tool against the wood in the neutral position with the flute closed. Be sure the bevel is rubbing. Then open the flute a small amount, and it should begin to cut. As this happens, move the tool sideways to advance the cut down the side of the piece, without changing the orientation of the tool relative to the wood.
If you open the flute but it doesn’t start to cut, the very tip of the bevel is probably not in contact with the wood. Don’t open the flute any more! Instead, swing the handle around to the right ever so slightly, and the cut should begin.
Caution: I’ve asked beginning turners at this point to “open the flute a bit more” only to have them rotate the tool a full 45º or so, which is way too much. This always gives me a bit of a scare because opening the flute makes the cut more aggressive and can easily lead to a catch. You must make adjustments to the tool position only in very small increments. This is the nature of turning.
After your initial success, try it again. Repeat the process of going from the neutral,
Chances are that as you advance the tool, the cut will either get gradually deeper or the tool will climb out and you will “drop the cut.” Either way, this issue will go away after you learn to guide the tool, which is explained a bit farther down. But first, a bit more explanation is in order.
Rubbing the bevel. Why doesn’t the tool dig into the wood, grab, and produce a catch? Answer: The part of the bevel back from the tip prevents this from happening.
In the first situation described above with the flute totally closed, all the bevel is simply riding on the surface. None of the cutting edge engages the wood, and the tool does not cut.
But when you open the flute a small amount, the very tip of the cutting edge on the top wing engages and begins to cut. Most of the bevel still rides on the surface and prevents the tool from being pulled deeper and deeper into the wood.
Now don’t try this, but imagine what will happen if you rotate the tool enough to cause the entire top wing to engage the wood (flute totally open). All the edge along the bevel will be actively cutting; none of the bevel will be left to ride on the surface and stabilize the cut. The tool will dig in, and you will get a catch.
The key to being able to control the cutting action is that as you open the flute, the active part of the cutting edge increases only gradually. Put differently, as you open the flute, the bevel riding over the surface does not disappear into the cut all at one time. This results from the geometry of the bevel angle and the shape of the flute.
Guiding a gouge in the basic cut. Three movements of the gouge control the direction the cut will take and how heavy or light the cut will be. One is the “rotation” of the tool about its length; this controls the extent to which the flute is open, as described above.
Another is aiming the tool in a direction relative to the length of the lathe. This is the “swing,” adjusted by pivoting the handle left or right. The third is tilting the handle so the long axis of the tool points either up or down. This is the “tilt.” (This terminology was introduced in Part 1.)
We can make two general statements about guiding the cut. We assume the tool handle is very nearly horizontal.
How heavy or light the cut will be is controlled by the amount the flute is open; that is, by rotating the tool around its long axis.
The direction the cut will take is controlled by the swing of the handle.
These two are not totally independent. If you swing the handle around to guide the cut deeper into the wood, you will get a heavier cut. On the other hand, swinging the handle to make the cut follow a curved surface does not produce a heavier cut.
Also, if you have opened the flute and established a fairly heavy (deep) cut, simply closing the flute will not necessarily cause the tool to climb out of the cut. You may have to guide it out by swinging the handle appropriately.
Changing the tilt. Lowering the handle shifts the active part of the cutting edge toward the bottom wing. This brings more of it into play and gives a more effective cutting action. For this reason, most turners naturally drop the handle a bit as opposed to keeping it horizontal as described above.
You can give this a try. With the lathe Off, place the gouge in the neutral position as described above, with the entire bevel in contact with the wood. Then lower the handle about 8º (see note below) and reposition the tool so the bevel is again in full contact. You may have to lower the tool rest slightly. Rotate the piece by hand and see if you get a shaving.
Find the neutral position where, with the bevel rubbing, the wood travels parallel to the cutting edge so that no cutting occurs. When you find it, remember it. This is your new starting position.
Note: OK, so how much is 8º? This corresponds to dropping the end of the handle about 2.5” if the overall length is 18”. Or drop the handle 2” if the overall length is 14”. This is not a lot.
Experiment a bit, rotating the lathe by hand, until you can go from neutral, where it doesn’t cut, to where it begins to take a small shaving as you open the flute. Then start the lathe and try it for real. After a couple of tries, you will probably find that this cut is no more difficult than with the handle horizontal, and it will more than likely work better.
After you get the hang of this, you will no longer need to start from the neutral position every time. You will be able to approach the wood with the flute already open so the cutting begins with the first contact. However, starting from neutral is safe.
Another note: When a gouge is used as described above, the cutting action occurs near the tip of the tool. In articles on this site, I will refer to this cut as being a tip cut to distinguish it from a wing cut where the cutting action occurs well out on a wing.
Up next: the wing cut.