For Band Saws That May Cut Faster and Straighter Without Wash boarding

Top illustration (at left): 2-1/4" tooth space is 106% of the 2-1/8" tooth space. These teeth are within the recommended limits.

Lower illustration (at left): 2-1/4" tooth space is 120% of the 1-7/8" tooth space. The much shorter second tooth may not be strong enough for the tooth bite required.

The performance of variable pitch band saws is usually best when, for every three consecutive teeth in the saw, the distance between the first tooth and the second tooth entering the cut does not exceed 115% of the distance between the second and third teeth.

Saw filers in the western USA are discovering that band saws with a variable tooth spacing, or pitch, often perform significantly better than conventional, evenly spaced, saw teeth. The two ways to grind these variable pitch saws with an Armstrong sharpener, reviewed below, are with conventional cams or special 5-lobe cams.

Why Variable Pitch Improves Saw Performance

Unevenly spaced saw teeth eliminate or dampen the harmonic vibration that causes "washboard" in band saws. The advantages of unevenly spaced saw teeth have been well known in the metal cutting industry for many years. In the 1980s, circular rip saws with unevenly spaced teeth were introduced in sawmills with excellent results.

Now, American saw filers are proving the advantages of variable pitch band saw teeth. Feed speeds may be increased. Washboard is eliminated or significantly dampened. Target sizes and kerfs may be reduced.  Some filers report performance is especially improved sawing frozen wood, indicating that variable pitch band saws should work well in hardwood sawmills, too.

How to Try Variable Spaced Saws Now

(without spending much money)

Sawmillers with Armstrong band saw sharpeners can explore the advantages of band saws with variable pitch teeth now by simply ordering new saws, available from a variety of vendors, and new cams from their local Armstrong Stocking Distributor/Service Center.

All genuine Armstrong cams will grind saws with a variable pitch tooth pattern. Most filers report they have the best success with a 5-tooth "segment" of variable pitch teeth. This segment usually has the longest pitch tooth entering the cut first, followed by the second longest tooth, and then the third longest tooth. The two shortest teeth in the segment are exactly the same. Then the 5-tooth segment is repeated. The saw length (or the spacings between the teeth) is adjusted so that the total number of teeth in the saw is evenly divisible by the number of teeth in the segment.

Grinding Variable Pitch and Depth Saws

On a No. 4 Armstrong Sharpener: Three Options Available

Armstrong has developed a system to grind variable tooth patterns where both the gullet depth and the tooth pitch change. This Variable Pitch and Depth (VPD) system is now available on No. 4 Armstrong sharpeners. Later in 1998, this system will be available for Armstrong No. 6 band saw sharpeners, too.

The special "VPD No. 4 sharpener" uses cams with up to five lobes so each gullet can be sized to match the tooth spacing. These saw teeth will be stronger and easier to maintain. Sawmillers will have the option of:

• Brand new sharpeners with this VPD option installed, or
• Late model factory rebuilt sharpeners with the VPD option installed or,
• A kit that can be installed in a late model No. 4 Armstrong sharpener that the sawmill already owns.

The preceding guidelines will help sawmillers evaluate the advantages of variable pitch saws in their mill. Saw filers will discover additional advantages to grinding variable pitch saws that also have variable gullet depths:

• The teeth are stronger, especially the teeth with the shortest pitch, when the gullet depths are proportional to the pitch.
• The tooth with the longest tooth pitch may act as a "raker" pulling sawdust out of the cut if the gullets for these long pitch teeth are deeper.
• The teeth will be easier to maintain when the gullet depths are more nearly proportional to the tooth pitch. The short and deep teeth made with conventional cams tend to have the backs ground away as the saws are resharpened.
• Variable gullet depths may further dampen harmonic vibration and washboarding the way that variable pitch dampens vibration.
• Higher feed speeds and better saw performance may be achieved if the longest tooth pitch could be greater than the maximum (153% of the shortest tooth space) allowed with conventional cams.

Ordering Variable Pitch Saws and Cams

When ordering cams and saws to test the advantages of variable pitch saws, consider the following guidelines:

• The cams should match the tooth with the longest spacing. This is usually about 1/4" longer than the single-spaced teeth being used now. For example, if the band saws are running successfully with a uniform 2" tooth pitch now, consider a variable pitch saw with the longest spacing about 2-1/4".
• For every three consecutive teeth in the saw, the distance between the first tooth and the second tooth entering the cut should not exceed 115% of the distance between the second tooth and the third tooth (see illustration).
• The shortest tooth pitch should not be less than 65% of the longest tooth pitch (or, this is the same thing: the longest tooth space should not be longer than 153% of the shortest tooth).
• Neither the gullet depth nor the wheel thickness should exceed 50% of the shortest tooth spacing.

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