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post #1 of 1 Old 06-26-2009, 02:07 AM Thread Starter
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Join Date: Jun 2009
Location: Huntington Beach, California
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Saw Blades

Before we get started lets think about a plane. It has nothing to do with a saw blade but everything to do with a saw blade.

We spend a lot of time aligning the knife in a plane to be EXACTLY square with the sole plate of the plane. When we plane, the plane works with the grain and produces fine shavings.

Think about that as we examine a table saw rip blade. The teeth of a rip blade (Raker teeth) are just like a plane. The raker teeth "plane" through and with the grain to produce fine shavings. A rip blade has large gullets to extract the 'with the grain shavings' efficiently.

If a rip blade is used in a cross cut operation the results are tear out and a poor cut.

A cross cut blade has teeth that are more like a knife edge and they cut rather than plane their way through a cut. Because these teeth are beveled at the top, they cut through the grain and produce fine saw dust. The cross cut blade has small gullets because the saw dust is smaller than that of a rip cut.

People have noted that a particular brand of saw blade makes their saw seem like it has more horse power or that the wood seems to feed through the cut so much easier. The truth of the matter is that the blade is being used to cut wood consistent with the design of the blade. The ease of feed doesn't make that particular brand of blade any better than any other. If the blade is being used as intended, obviously, it is going to work and feel better.

The general purpose blade (Sometimes incorrectly called a combination blade) that will work well for both cross cuts and rip cuts. These blades usually have alternating top bevel teeth and a tooth count from 40 to 60 teeth in a 10" blade. It should be noted that the shallower the angle of the top bevel, the better the blade will perform at rip cutting. (Think of the plane example, above.) The more acute the angle of the top bevel the better the blade will perform at cross cutting. There are other geometric tricks that can be used to improve the cutting efficiency of a blade.

A geometric trick is to angle the face of the tooth relative to the blade disk. This leaves a larger area for sawdust during a rip cut.

The tooth of the blade can lean forward into the cut (positive hook angle) for a more aggressive cut. Generally speaking, table saw blades have a positive hook angle. (Hook angle is measured from a radial line of the saw blade.) Radial Arm Saws and miter saws usually use a negative hook angle. The more negative the hook angle, the smoother the cross cut but the slower the cutting action. A RAS or miter saw blade can be used in a table saw but the reverse is not true.

Everything above is an explanation of the compromises involved in saw blade manufacture and selection. Do you want to change blades for each type of cut? Are you willing to settle for slower, less efficient and lesser quality cuts? Only you can decide.

There is one more compromise. The blade is called the combination blade. It is different than the general purpose blades described above. This blade has both raker and ATB teeth. It performs well and has the advantage that the cut is much flatter than a general purpose blade. The raker teeth tend to make the kerf almost flat bottomed. The cut looks like bat ears extending above a flat top hair cut.

Generally speaking the true combination blade is better at rip cutting but it also makes cross cuts very well. The combination blade with its raker teeth seems to be the ideal blade for most home shops and many commercial shops. I find that this blade just works better in my shop. In my shop, the vast majority of table saw cuts are rip cuts so I lean toward the combination blade. As they say, "Your mileage may vary."

There seems to be a urban myth about the number of teeth on a saw blade. The more teeth on the blade, the better the cut. Nothing could be more from the truth. It is a blade with the correct type of teeth for the cut being made that gives the best cut.

If you are cutting trees in a forest, you may want a 36" blade with 18 teeth. If you are making mitered picture frames you may want a 12" blade with 120 teeth. The choice of the blade corresponds to the intended use of the blade.

The big screaming message is, "Everything is a compromise!"

Use the right tool for the job.

Rich (Tilting right)
Huntington Beach, California
Remember that when we have the "BIG ONE" everything east of the Rockies falls into the ocean.
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