Adjusting the Mouth on a Plane

Using a well tuned hand plane to shave wood is arguably one of the most seductive pleasures in woodworking, but it takes some knowledge and a little effort to get the hand plane tuned properly. One aspect of using a plane that requires regular attention is the mouth opening. Most hand planes have a fixed mouth opening that is not easily adjustable. In fact, that style of mouth can only be adjusted by opening it wider using a file, so when you are setting the opening for that style plane, choose the opening size wisely and sneak up on it through repeated testing. But some planes, such as the one that Rob Johnstone is using here, have an adjustable mouth opening that can be adjusted for the task at hand.

Understanding the concepts that determine your optimal mouth size is important before making any adjustments. The variables to keep in mind are:

Grain orientation. The direction of your planing action relative to the direction of the grain will be a determining factor when setting the mouth size. Rob explains the trade-offs here and helps you understand the fundamentals.

Debris size. Some planing operations are intended for a finishing step that involves light removal of stock, while others are intended for fast removal of large amounts of material. These two types of planing will result in shavings that can vary a lot in size, so it will be important to have the plane’s mouth opening set to accommodate the size of debris.

Excess opening leads to lower quality surface. While it might be tempting to just use a large opening that will accommodate any chip size, you will find that using a large mouth opening for fine stock removal operations can lead to less than perfect results. Therefore it is important to use the right size mouth opening for each planing situation.

If you are interested in learning more about hand planes and other useful hand tools, check out our class on using hand tools.