Sawmilling Concepts
Part II: Sawing Lumber Using the Quarter Scales 

This article is the second in a series of reports that will appear in the S&W Report, focusing on sawmilling concepts.  The purpose of the series is twofold.  It will provide some useful tips to those who own a portable sawmill. It will also assist landowners who may want to purchase a mill or hire a sawyer in gaining a better understanding of proper sawing techniques. 

Topics covered in the series include: sawing lumber, using the quarter scale, saw blade maintenance, introduction to drying lumber, determining moisture content of wood, wood drying defects, methods of drying lumber and dry kilns.

In Part II, we will examine sawing lumber using the quarter scales.
Quarter scale – a graduated ruler which indicates the correct positioning of the saw blade for a variety of thicknesses (e.g., 6/4 scale is used for cutting 1-1/2" thick lumber).

The quarter scale includes the thickness of the finished board, the saw kerf, and the allowances if needed for shrinkage and planing.

Sawing Lumber Using the Quarter Scales

Many sawmills are equipped with graduated scales that assist the sawyer in positioning the saw blade for each cut.  In this article, you will learn why quarter scales are used when milling lumber.

The quarter scales are based on the premise that a circular saw will remove a 1/4-inch kerf from the log with each pass of the blade. 

Therefore, the sawyer needs to calculate the next position of the blade by always adding on the kerf of the saw (1/4-inch). He also has to make the required allowances for eventual board shrinkage and possible planing (an additional 1/16 to 1/8 of an inch). 

For example, if a sawyer were sawing 2-inch boards from an 8-inch tall cant, he would need to calculate the number of available cuts based on the depth of the cant by making allowances for saw kerf, planing and shrinkage.  The sawyer would have to make the following height adjustments to saw the 2-inch boards (all measurements are based on the height above the sawmill bed).  First, the sawyer would cut at the 6-1/2 inch mark (note: in this example no allowances are being made for shrinkage or planing), the second cut is made at the 4-1/4 inch mark, and the third and final cut is made at the 2 inch mark, resulting in a board remaining on the sawmill bed 2 inches thick.  In this example the sawyer was able to cut three 2-inch boards from the 8-inch cant.  The amount of material lost to saw kerf was ¾ of an inch (3 cuts each having a ¼ inch kerf). 

As you can begin to appreciate, if one was required to calculate the proper sawing measurements for each turn of the log, one would find it a slow process ripe for potential fractional mistakes!  This becomes increasingly apparent when one is cutting a combination of boards of different thickness (e.g., 1", 1 ¼”, 1 ½” and/or 2" thick). 

To simplify this process, the quarter scale was devised.  The scale (Figure 1) shows tick marks where the sawyer needs to position the blade in order to make accurate cuts of the desired thickness.  The distance between each tick mark on the scale includes the desired thickness of the board and allowances for saw kerf, shrinkage and possible planing. The allowances made for planing are usually reserved for lumber destined for cabinetry and furniture manufacturing. Lumber for timber framing quite often is not planed.

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Figure 1: This illustration shows a standard quarter scale (sawmill blade scales) with its actual measurements.
It should be noted that the quarter scales have been revised for bandsaw mill operators because the kerf on this type of mill is much smaller.  For example, a circular saw’s kerf is ¼ inch versus a kerf of 1/16 inch for a bandsaw mill.  A 4/4 board (1inch finished thickness) on the Standard Quarter Scale is set to cut at a thickness of 1-1/8 inches, producing a piece of lumber from the sawmill 1-1/16 inches thick   (1/16 inch will be lost for saw kerf).  Refer to Table 1.
Now that you have a general understanding of the quarter scale you can test your skills in reading it correctly.  Referring to the illustration in Figure 2, can you answer the following questions?

1) What is the actual thickness of the cant;

2) How many 2 inch boards can one saw from the cant;

3) How many 1-1/4 inch boards can one saw from the cant;

4) How many 1 inch boards can one saw from the cant; and

5) How much material is lost for saw kerf if one were to saw the cant into 4/4 lumber assuming 1/16 inch saw kerf?

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Figure 2: A cant beside a quarter scale (diagram is to scale).

In the Next Edition

In Part III of the series, we will look at saw blade theory and terminology, a key component to successful sawmill operations.  In this article information will be presented on the proper maintenance of saw blades.

Answers: Question #1 – approximately 5 –1/4 inches, Question #2 – two boards, Question #3 – three boards, Question #4 – four boards, and Question #5 – four cuts x 1/16 inch = 1/4 inch.

Acknowledgement

The information (including illustrations) for this article is from the Instructional Guide to Wood Technology and Sawmilling, 2000.  A publication of Wood-Mizer Canada Co, 217 Salem Road, Manilla, Ontario, K0M 2J0, 1-877-866-0667, <www.woodmizer.ca>.

This article appeared in the Fall/Winter 2004 (Volume 37) edition of the S&W Report the newsletter of the Ontario Woodlot Association.

© Ontario Woodlot Association

Visit the ‘S&W Library’ section of our website for the article Sawmilling Concepts – Part I: Lumber Sawing Techniques.

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