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Doc Green’s Woodturning Site

Parting Tools

What’s a parting tool used for?   The traditional purpose is to cut a narrow slot in the workpiece in order to separate it from waste wood.  Accordingly, the tool is long and narrow so it can reach deep into the cut.  Thicknesses range from a minimum of 1/16” up to 1/4” although similar tools intended for other purposes may be a bit wider.  For strength, the “blade” of a parting tool is wide, and the cross section is typically rectangular.  

A parting tool is also used to cut narrow slots wherever such a slot is needed.  For example, slots may be cut into a spindle blank to establish the diameter the spindle is to have at that point.  Another use for the wider tools is that of removing wood quickly when forming a tenon.  

A diamond parting tool has a flattened-diamond cross section. This geometry provides relief in the cut and minimizes frictional forces against the sides of the tool.  I think this is the first parting tool that a new turner should acquire.

Safety note:  You must not advance a parting tool into the wood more than a fraction of an inch without widening the cut to provide relief, for two reasons.  First, friction against the sides will cause the tool to get hot – hot enough to cause a burn if you are unaware.  

Second, the friction force causes the tool to be hard to control, and in the worst case, the wood may grab the tool and take it away.  Some have rather short handles and are not intended to reach far over the tool rest nor deep into a cut that has not been relieved.  

Using a Parting Tool

Zero shear.  A common feature of all parting tools is that the wood meets the cutting edge straight on.  There is no shearing action at all.  It follows that the surface produced will not be as clean and smooth as that produced by a gouge or skew.  (This is not true for the beading/parting tool when it is used more like a skew.)

Thin parting tools.  These are intended primarily for making thin parting cuts to separate a piece from waste wood.  The cut is made at center height with the handle of the tool level.  The cutting action can be scraping or bevel-rubbing, depending upon the geometry of the tool.  In this application, the quality of the surface left behind is not a major concern.  

The procedure for making a cut is exactly what you might expect. You place the cutting edge against the wood at center height, and then advance the tool into the cut.  If you feel a strong downward force on the tip of the tool (handle tends to rise), the indication is that either you are advancing the tool too fast or you need to drop back and widen the slot, for relief.  

Thicker, symmetrical-bevel tools.   These tools may be used at center height in the same manner as the thin tools, but a more effective and efficient cut is the peeling cut.  This cut is made well above center and is best when done with the lower bevel rubbing. It will remove wood quite rapidly and leave a cut that is flat on the bottom.  It is therefore widely used for cutting tenons.

My observation is that a parting tool in a peeling cut is stable and shows little tendency to grab and produce a catch.  

When you are cutting slots that will become a permanent part of the piece (as with a honey dipper), you can avoid tearout by using a skew to incise lines at each edge of the slot.  This is described in the article on skews.  

Shop-made parting tools.  The best parting tool I have is one made from an old file.  It takes a good edge, holds it well, and is stiff so that sideways flex is never observed.  

Conventional wisdom holds that files are brittle and will break easily.  For this reason, I do not use files to make scrapers or other tools that will be used flat on the rest.  This is the weak direction as far as the file is concerned.  However, for the parting tools, the file is used “on edge,” which is its stronger direction.  In any case, I am one who seldom takes a heavy cut, no matter what the tool.

I also have one made from a cheap pilot hole bit, one that’s flat and never works quite as well as you had hoped.  Also, I made a long skinny one from a triangular file.  These work well for their intended purpose, which is to make small cuts on tiny pieces.

(See the first photo in this article.)

A beading/parting tool.  These tools have symmetrical bevels formed on a body having a square cross section, available in sizes of 1/4” and 3/8” square.  They are widely used for forming tenons with a peeling cut.  

A more exacting application is that of “rolling beads” on a spindle. This terminology arises from the motion the tool executes while shaping a bead.  The method is to use the tool to cut a pair of convex surfaces back to back, which constitutes a bead if the spacing, curvature, and so forth are correct.  

The tool may be considered to be a variation of a skew.  For example, it will do a nice planing cut on a small-diameter spindle and will cut V grooves as long as the groove is not too narrow.  To perform at its best, it needs to be sharpened to the same degree as a skew.  However, the angle between the bevels is about twice that of a skew and this affects, to some degree, the sharpness of the edge that can be achieved.  On the other hand, the larger angle makes for a strong cutting edge.

To me, it is easier to use than a skew, probably because I have a better concept of exactly where the bevel is that is supposed to be rubbing the surface.  With the skew, I always feel like the bevel is hidden and I’m working blind, but this is no doubt just a mental thing.  The one disadvantage it does have is that, because of the greater bevel angle, the handle must be swung farther to the left or right in order to bring the plane of a bevel square to the axis of the piece.   

Using the B/P tool to cut convex surfaces.  Mount a small spindle blank on the lathe and true it up.  Adjust the height of the tool rest so it feels comfortable when the bevel rubs at about the 10 o’clock position.  Use a peeling cut to form a groove about 1/4” deep near the middle of the piece.  

With the lathe Off, place the tool about 1/2” to the right of the groove and find the position where the cutting edge just begins to engage the wood, with the bevel rubbing.  Remember this position because it’s where you start when you “roll” a convex surface.  

Swing the handle to the right about 10º and rotate the tool slightly to the left.  The left corner of the cutting edge should now be in contact with the wood, bevel still rubbing.  Rotate the lathe by hand and the cut will begin at the left-hand side of the cutting edge.  

Now start the lathe at a few hundred RPM.  Place the tool about 1/4” to the right of the groove.  Swing the handle to the right and rotate it to the left as before to initiate the cut.  Then advance the cut toward the groove by pivoting the tool on the tool rest.  The result should be a surface that slopes toward the groove.  

To create a curved surface, continue rotating the tool as you pivot the tip to the left. As the curvature develops, you will have to swing the handle to the left at the same time in order to keep the bevel rubbing.  If, by chance, you get a runback, the indication is that you are swinging the tool too far to the left.  

Practice this cut until you are comfortable with it.  If you have trouble, use a gouge or whatever tool works for you and cut a curved surface.  Then, with the lathe off, roll the B/P tool over the surface and study the positions the handle must assume in order to keep the bevel rubbing and the left side of the cutting edge in contact with the surface.  

As your confidence develops, cut a deeper groove and try for a surface with greater curvature.  And don’t forget, learn to make the cut on the other side of the groove, advancing the cut to the right. After all, a bead has two sides.  

Cutting a bead.  On a practice spindle, use a parting tool to cut two grooves near its center about 3/8” apart and 5/16” deep.  Then use the B/P tool to round the sides of the center ring to form a bead.  As you do this, practice looking at the “horizon” rather than directly at the cutting edge; that is, look across the top of the spindle where you can see the curve in profile.

Now to do the other side . . .

Chances are that you will wind up with rounded sides, but the shape will not look much like a bead.  You will note that the tool handle must swing a lot to get steep sides on the bead.  

Now move to the side of one of the groves and cut another. Try it again.  Any improvement?  Keep on doing these practice cuts until you get a good-looking bead, or at least a curved surface that could be whipped into line with sandpaper.  

Next, instead of using a parting tool to cut a fairly wide grooves on each side of the bead, use a skew (or the B/P tool) to cut fairly wide V grooves.  This should have the effect of bringing the beads closer together.  

The following three shots illustrate the rolling motion of the tool as it advances in the cut.                           x

As you make progress, make the V grooves narrower until the resulting beads are practically touching at their bases.  Then practice, practice, and practice some more.  Try making tall beads, short beads, wide beads, narrow beads, and for fun, elliptical beads.  Also, concentrate on getting a clean surface so that little sanding is required.

If the angle of your B/P tool is so large that you have trouble reaching to the bottom of the cusp between the beads, feel free to use the long point of a skew to clean up that region.  And that’s all there is to it.  

Easier said than done?  Yes, perhaps.  I’ll admit to having my own difficulties in getting  good curves and making two beads that look remotely the same, but then, I need to practice a bit more.  

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