American Woodworker

Free Product Guide >>

Syndication

 


 

 

 

Woodwork 

Winter 2013-2014

Preview this issue

 

Sharpening Gouges

RATE THIS:

Sharpening Gouges

By Alan Lacer


Perhaps no other aspect of lathe work is a bigger stumbling block to new turners than the process of shaping and sharpening the tools. Even new tools often require reshaping and tuning to make them truly serviceable. A poorly shaped or dull tool is hard to control and leaves a damaged surface that requires extensive sanding. On the other hand, a sharp tool, ground properly for its intended use, is almost effortless to handle and leaves a fine finish on the wood. The following is my suggested strategy for a sharp and user-friendly spindleroughing gouge and detailing gouge—two of the most common turning tools.

 

Sharpening equipment

Here’s what you’ll need:

• A slow speed (1,725 or 1,800 rpm) wheel grinder with 8-in.-dia.wheels. The tool rests must be rock solid,with no flex whatsoever. If your rests are flimsy or too small, consider adding an aftermarket support (see Sources, below).

• A 1-in. wide, 60-grit wheel of friable (easily crumbled) aluminum oxide (white,pink or blue) in a J or K hardness.Although 60 grit may be too coarse for carving tools, chisels and plane irons, it is a good choice for the heavier turning tools. It removes material more efficiently and grinds cooler than finer grits, while still leaving a fine edge on the tool. In addition, have a coarser wheel (36 or 46 grit) on the other side of the grinder for those times when heavy stock removal is necessary.

• A dressing tool is essential. Use it to true (make the wheel round), clean, sharpen and level the wheel.Gray dressing sticks, star-wheel and diamond dressers are the choices. Each leaves a different surface on the wheel,but any one can fit the needs of most woodturners.

• You also need a medium India slipstone for refining the ground edge and for maintaining a sharp edge between trips to the grinder. See Sources,page 23, for a mail-order source for all of the equipment.

 

Types of gouges

Turners use three basic gouges: the spindle roughing gouge, the detailing gouge and the bowl gouge (Photo 1). In this article,we’ll cover how to sharpen the first two. Sharpening bowl gouges is a subject all to itself,which we’ll cover in a future issue.

The spindle-roughing gouge is used for between-center work to remove the corners from square stock, turn cylinders, tapers and long shallow curves. It is a poor choice for detailing or bowl work because it does not maneuver well in tight turns and is subject to breakage at its tang.

The detailing gouge (sometimes called a spindle, shallow or fingernail gouge) is a workhorse for between-center work, readily suited to concave and convex details, and sometimes used in bowl work for fine detailing.

 

General grinding strategy

1. Begin by dressing the wheel. A level and sharp grinding wheel is essential to proper grinding. Keep your dressing tool beside the grinder and use it frequently to remove build-up of metal (glazing) and to maintain the flatness of the wheel. For safety, protect your eyes and lungs with safety glasses or a face shield and dust mask.Position the tool rest as close to the wheel as possible.

2. Shape the tool first. Set the tool rest at 90 degrees to the coarse wheel and begin shaping. See Figs.A and B (below) for suggested shapes and bevel angles of the spindle-roughing gouge and the detailing gouge.

3. Begin the sharpening process. Set the tool rest at the desired angle for the finished bevel on your 60-grit wheel. Always begin at the heel (Photo 5).The process proceeds in stages until the entire bevel is in full contact with the wheel. In reality, you are grinding the bevel and not the edge.As experienced turners say, “If you grind the bevel properly the edge will take care of itself!”

4. Use light pressure, be slow and deliberate and maintain a relaxed grip (and attitude!).Maintain a solid stance with elbows against your body.Use only the force required to eliminate any tool bouncing.

5. Leave the tool on the stone, checking your progress only occasionally. Use the spark trail as the indicator of where you are grinding.When sparks begin to lightly run over the top of the tool, stop grinding in that area—otherwise you will burn away the steel and produce a “saw-toothed” edge.

6. Avoid heating the tool to such a temperature that you see temper colors developing (yellows, purples, and blues). Such overheating does not harm high-speed steels (usually so stamped on the tool or its handle),but bluing an edge on a high-carbon tool creates a tool too soft for turning wood.A clean and sharp wheel, light pressure and even movement should not overheat the steel.With carbon-steel tools that must be heavily ground, are thin or delicate (like the points on skew chisels), quench the tool in water often to keep the steel temperature low. For high-speed steel tools,do not quench in water.Quenching these tools may create micro cracks that affect the quality of the edge. For these tools, simply do heavy grinding in stages, allowing the tool to air cool between sessions.

7. The objective of sharpening is to produce a keen edge with a bevel that is single-faceted with a slight hollow grind.


The Spindle-Roughing Gouge

Probably the easiest gouge to grind is the spindle-roughing gouge. Shape the tool as recommended in Fig. A. After setting the rest to 45 degrees, start at the back of the bevel (heel) and rotate the tool side to side along the full length of its edge. Grinding is complete when the full bevel is in contact with the wheel and sparks appear over the top of the edge (Photos 5 - 7).


The Detail Gouge

If you sharpened this tool with the same technique used for the roughing gouge, you would produce a spear-pointed shape, instead of the desired fingernail shape (Fig. B), because most of these gouges are thinner on the sides and thicker in the middle. Set the tool rest to 30 to 35 degrees, and follow photos 8 through 10.Start at the heel of the bevel, with the flute upright. Do each half of the tool by pushing upwards with a slight twist.When each half has been ground, blend them together in the middle of the tool.


Is it sharp?

Here’s how to tell if your tool is sharp:

• By sight: If you can see the edge, there is no edge! A sharp edge reflects no light, but simply disappears into a black line. Angle the tool edge under your shop lamp to see if you pick up any glints of light.

• By effort to remove wood:A sharp edge, with the tool at the proper angle, makes turning wood feel effortless. A dull tool requires more pressure to make the cut.

• By sound: A sharp tool makes a hissing sound (reminds me of a sharp hand plane) while a dull tool sounds flat or makes a scraping sound.

• By shavings: A sharp tool makes curls and ribbons (even if short at times).A dull tool makes very short chips or even dust.


To hone or not to hone?

Not every turner hones their tools, either after grinding or when in use. Over the years I have found honing helpful in several regards: To refine an edge for a finishing cut; and to maintain a sharp edge, rather than returning to the grinder at the first hints of dullness.Honing only works on properly ground tools. Bevels that are multi-faceted or lack a hollow grind are difficult or impossible to hone. For gouges I use the flat side of my India slipstone to hone the ground bevel, and finish with the curved edge of the slipstone in the flute of the gouge (see Fig. D). Take great care not to round over the edge when honing. Hone the bevel and flute of the gouge and never the edge itself.


Sources

(Note: Product availability and costs are subject to change since original publication date.)

Gouges and sharpening equipment are available from many mail-order sources. For example:

Woodcraft, woodcraft.com, 800-225-1153, 8-in., slow-speed grinder, #127255; 60-grit aluminum oxide white wheel, #01W48; 36-grit aluminum oxide blue wheel, #129760; Grinding tool rest, #03B35; Dressing stick, #11N51; Diamond wheel dresser, #124670; Medium India slipstone, #07B05.


Fig. A

The spindle-roughing gouge is generally ground straight across (as viewed from above), with a vertical or near-vertical edge (as viewed from the side) and with a 45-degree bevel angle.


Fig. B

The detailing gouge is commonly formed into a fingernail shape (as viewed from above) and with a 30- to 35-degree bevel angle.


Fig. C

Hone the bevel of a gouge with the flat side of the slipstone.The hollow ground edge makes for a built-in honing jig: Simply touch the heel of the bevel with the stone.Then lower the stone until you feel the area just below the edge.Maintain contact with those two points and progress along the bevel until the entire edge has been honed.


Fig. D

Hone the flute of the gouge by using the curved edge of the slipstone. Hold the stone completely flat inside the flute and progress along the edge until the full length has been honed.


This story originally appeared in American Woodworker June 2000, issue #80.

June 2000, issue #80

Purchase this back issue.

Click any image to view a larger version.

1. The three basic types of gouges are the spindle-roughing gouge (English style), the detailing gouge and the bowl gouge.


2. A properly dressed wheel is essential. Hold the dressing tool firmly and move side to side across the wheel until it is flat and clean of all metal particles.


3. The first step in sharpening any gouge is to create the shape of the tool. Detailing gouges, for example, come from the factory square, triangular or slightly domed (left). The correct shape is like a fingernail (right).


4. Rotate the tool slowly along the full length of the edge, progressing until the entire bevel is in contact with the wheel. Maintain a comfortable grip, keep the tool rest set to 45 degrees and the heel of the bevel resting on the wheel.


5. As seen from the side, the roughing gouge’s first contact should be at the back of the bevel (heel).


6. As the rotation continues, the mid-section of the tool is ground.


7. The bevel is now in full contact with the wheel and sparks are just beginning to appear over the top of the edge.


8. Start with the gouge in the middle of the stone with the heel of the bevel touching the wheel.


9. Grind the left half of the tool by slowly pushing the tool up the stone and rotating to the left. Reverse this action to return the tool to the starting position.


10. Grind the right half of the tool by slowly pushing the tool up the stone and rotating to the right.

Then reverse this movement to return the tool to the starting position.This sequence may have to be repeated several times to achieve a sharp edge. When the bevel is in complete contact with the wheel and sparks just begin to trail over the top of the tool, you’re done.


11. Gouge grinding pitfalls. Rookie attempts at grinding often produce these problems, from left to right: 1. Multi-faceted gouge (uneven movements and pressure, removing tool too frequently from wheel to examine and attempting to return to same place). 2. Spear-pointed detailing gouge (failing to grind to the shape of the edge). 3.Tool bluing (dull or loaded grinding wheel, excessive pressure, grinding in one place too long), and a saw-toothed edge (over grinding of the edge, usually indicated by a stream of sparks over the top of the tool).