Mastering the 40/40 Grind: The Ultimate Guide to Sharpening and Technique

If you’ve been in the woodturning world for any length of time, you’ve likely heard of the 40/40 grind. Popularized by professional turner Stuart Batty, this specific geometry for the bowl gouge is often called the “holy grail” of grinds.

But for many, the 40/40 has stayed out of reach because it has traditionally required a high level of freehand sharpening skill. At Craft Supplies USA, we’ve been working to change that.

In this guide, we’ll break down what the 40/40 grind is, why it’s a game-changer for your turning, and how you can achieve it perfectly every time using the new 40/40 Raptor Jig.

What is the 40/40 Grind?

The name “40/40” refers to the specific geometry of a bowl gouge:

1. A 40-degree nose bevel.
   
2. 40-degree straight wings.

To achieve this, you must use a gouge with a parabolic or elliptical flute. Traditional V-flutes or U-shaped bottoming gouges don’t have the wall thickness or shape required to make this geometry work.

Why Use It?

The 40/40 grind was born out of a need for speed and efficiency. Stuart Batty developed it while doing production spindle turning for his father. He needed a tool that could:

• Remove massive amounts of material quickly (peeling cuts).
  
• Leave a finish-ready surface on difficult end-grain fibers (slicing cuts).
  
• Reduce fatigue by requiring half the physical energy to make a cut compared to traditional grinds.

How to Sharpen the 40/40 (The Easy Way)

The biggest barrier to this grind has always been the sharpening. Most jigs are designed for “Irish” or “swept-back” grinds. To solve this, we developed the 40/40 Raptor. Here is the step-by-step setup:

1. Establish the Wings

The foundation of the 40-40 grind is a perfectly straight cutting edge along the wings. Using your sharpening platform, set the tool so the wing is flush against the stone.

• Grinding wheels naturally create a “hollow” or concave shape. To counter this, slightly rock the gouge up and down on the platform to flatten the wing out.
  
• Use a straight edge to check your progress. You want a crisp, linear edge from the nose to the back of the wing—once this geometry is established, you won’t have to reprofile it often.

2. Set the 40/40 Raptor

Move the platform aside and bring in your V-arm and the 40/40 Raptor.

• Set your tool to a 3” protrusion from the jig.
  
• Set your Vari-Grind leg angle to 17 degrees (all the way to the top).
  
• Use the Raptor to set the exact distance of your V-arm from the wheel.

3. Grinding the Wings in the Jig

Before you focus on the nose, you want to use the jig to refine the wings. While the platform gave you the straight shape, the jig ensures the angle is perfectly consistent.

• Keep one hand on the V-arm for stability while your other hand swivels the tool.
  
• Rotate the tool to one side and bring the wing into contact with the wheel. Instead of a “sweeping” motion used for fingernail grinds, you are essentially refining the flat surface you created in Step 1.
  
• Work one wing, then the other. Monitor how much steel you are removing to ensure both sides stay the same length. You want the wings to be mirror images before you ever touch the nose to the stone.

4. Blend the Nose

With light pressure, sharpen the nose and blend it into those straight wings you established on the platform. Avoid “over-rotating” into the wings, or you will accidentally change that 40-degree angle.

Putting the 40/40 to Work: 3 Essential Cuts

Once you get to the lathe, you’ll immediately feel the difference. Here are the three areas where the 40/40 excels:

1. The Production Peeling Cut

On a spindle, the 40/40 acts like a “sledgehammer.” By opening the flute and using the wing, you can peel away deep shavings. Because the wing is straight, it acts like a Bedan or a Skew, clearing material with incredible efficiency.

2. Slicing End-Grain

One of the most impressive feats of the 40/40 is its ability to slice end-grain fibers cleanly. By arcing the tool toward the center (similar to a skew technique), the nose slices through the fibers while the wing acts as a chip breaker. The result is a surface that often only needs a light touch of 320-grit sandpaper.

3. The Controlled Push Cut on Bowls

When roughing out a bowl, the 40/40 feels “planted.” Unlike rounded “fingernail” grinds that can feel skatey, the 40/40 locks onto the bevel. You can remove bulk material from a wet blank with minimal effort and zero “white-knuckling.”

Final Thoughts

The 40/40 grind isn’t just for pros—it’s for anyone who wants to spend less time sanding and more time turning. While it doesn’t replace every tool in your kit (it’s not ideal for shear scraping on bowl exteriors, for example), it will likely become your go-to gouge for 90% of your work.