What Is Kerf and Why Is It Important?

If you’ve been interested in sawmills for any length of time, you have likely seen the term “kerf” floating around. Did you ever wonder what that term meant? Simply put, kerf is the term for the width of the saw cut and the associated volume loss that occurs from sawing or milling. It is the amount of wood lost to sawdust, so to speak. The issue of kerf is not unique to sawmills, however. Carpenters, machinists, and metal workers also use the term to describe identical issues of volume and material loss with their respective tools. In these cases, kerf primarily presents a problem of measurements. A carpenter wishing to make an exact cut must consider, for example, that the width of his saw blade will remove about 1/8th of an inch of material. For a sawmill, kerf presents a different, but just as crucial problem: Efficiency.

Kerf Affects the Efficiency of a Sawmill

Sawmilling can be a tough business. Margins can be tight, and sawyers must waste as little as possible, both in terms of time, money, and materials. Kerf is itself a big source of waste. The kerf of a single cut may not seem to be much, but consider that many cuts will be made through a single log. Added together, this volume could amount to an entire board lost from every log! That’s a huge difference.

Second only to slab wood, kerf represents one of the single largest sources of physical waste in a modern sawmill operation. Unfortunately, it is an inherent cost of doing business. A sawmill must cut wood, and unless the physics around sawmill technology changes dramatically, a certain percent of log volume will always be lost to kerf.

Sawdust Itself Is a Problem

The problem kerf presents is twofold: of course, its bad to lose good volume to sawdust, but then what do you do with sawdust? The accumulation of those pesky particles has long been a source of grief for sawmill operators everywhere. In most cases, there is not much you can do with sawdust, and so disposal can create a costly problem. Luckily, forestry workers are some of the most creative, and sawmills have been able to create markets for this material, helping to alleviate the problem.

What is the Kerf of a Sawmill Blade?

It should be no surprise that the width of kerf is variable between different machines. Milling with a bandsaw mill may create kerf totaling 12% of the total volume. With a circular sawmill, however, up to 21% of the volume may be lost to kerf. That said, there is an industry standard of sorts. The International 1/4″ international log rule is largely the standard for estimating the board foot volume of logs, and its key assumption (included in the name) is a 1/4″ kerf. That is a decent rule of thumb to use for log rules, but it can be problematic in most cases, as it tends to be an over-estimation.

It is important to know the peculiarities of your specific machine so you can get the best estimate possible. Here are some generalities for different types of sawmills:

Band sawmills

Band sawmills are by far the most efficient on the market when it comes to kerf reduction. Coming far below the 1/4″ standard set by log rules, many band saws come in with a kerf around 1/16″. Ultimately, however, the number will depend on both the physical width of the blade and the tooth set, which is the angle at which the teeth are angled outward.

Band sawmills have a relatively narrow kerf.

Circular Sawmills

These days, circular sawmills are mostly antiques. They are substantially less efficient than modern band sawmills both in terms of the power needed to operate them (surprisingly, giant metal spinning disks need a lot of power), and of course the kerf. In fact, the 1/4″ international log rule was largely developed during the days of circular sawmill dominance, so it is from these mills that the rule gets its assumption. That said, one can expect a 1/4″ kerf with a circular sawmill, though variability of course still exists.

Circular sawmill diagram.
Old Diagram of a Circular Sawmill Layout

Chainsaw Sawmills

Coming in unsurprisingly as the most inefficient sawmill on the market is the chainsaw sawmill, also known as “Alaskan mills,” sporting an unadmirable kerf of 3/8 inches. Yikes. But most people who use these mills are not overly worried about efficiency. Chainsaw mills have the benefit of extreme mobility, simplicity, and adaptability, making them perfect for the unsupported backwoods, hence the more colloquial name. Generally speaking, where these are used, timber is not in short supply, and kerf is not much of an issue.

Chainsaws have a very large kerf.

The Best Way to Reduce Kerf Inefficiency

Given the information above, it should be no surprise that the best way to reduce kerf is to use a band sawmill with a thin blade. Beyond that, kerf is an inherent cost of doing business for sawmill operators everywhere. However, you can reduce the impact it has.

Earlier, I mentioned that sawmills must develop an economical system for the disposal of their sawdust. This is a practical way of reducing waste for sawmills both large and small and potentially even generating more profit. For example, a small pellet mill can easily be purchased to turn this waste material into usable (or sellable) pellets for heating. Sawdust and shavings can even be sold to farmers and hobbyists as animal bedding. There are many possibilities, but anything you can do to turn kerf waste into profit is going to be crucial to the success of your sawmilling endeavors. Don’t fear kerf: understand it, and then control it!

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