Notice from my profile that I am a serious woodworker and because of that, I thought that I should do a series on the many myths surrounding "Saw Blades". I am going to number these different myths so that I can easily refer do different ones over the course of these blogs. I may get a little scientific at times, but bear with me, I will try to make it easy to understand..
When I was a kid, I recall that my uncle heated with wood and that he had a "buzz saw" that he used to cut his wood up into small pieces. If you have ever been around one of these, you know how dangerous it can be. It has a blade at least 3 feet in diameter with big ugly teeth. My uncle's was run off the flywheel on his tractor using a big flat belt, so you know that it had a lot of power. The main thing that I remember is the "sound" that the blade made. If you ever heard a "buzz saw" running, I know that you remember that sound. It was a loud ringing sound that could only come from a "buzz saw". Now, you may ask why the sound of a "buzz saw" is such a big deal? I will explain that as part of myth #1.
If you know anything about music, then the following will be easy to follow. I might note, that as part of my woodworking, I make custom classical guitars. Using the guitar as an example, you know that each string has it own sound or vibration frequency. The fat strings are lower pitched and they vibrate slower than the thin strings that are higher pitched and vibrate faster. If you pluck the string softer or hard, the pitch is still the same. If we look at the violin, we don't actually pluck the strings, we run a rosined bow across the strings. What the bow does is to pluck the string millions of times in a random fashion. This we call "white noise" and the string vibrates according to its length and tightness, not how hard or soft you run the bow across the strings. The more of this "white noise" or energy that you put into the violin, the louder that it sounds. The sound gets louder as the string vibrates a greater and greater distance. It is a little like swinging in a playground swing. You might swing just a small amount or very high, but it always takes the same amount of seconds to make one full swing. Are you with me so far? Now back to the saw blade.
Just like the swing or the strings on a guitar or a violin, each saw blade has its own pitch. Remember the "buzz saw"? When you first turn on you table saw, did you notice that you can hear the ringing of the saw blade as it runs? Try different saw blades and you will find that each one vibrates at it own pitch. I know that most of you think that all saw blades do this ringing, but there are some that don't! I will get into that in another blog. Just like the guitar or the violin, the more white energy that you put into the blade the greater the sound and the distance that the blade vibrates, like the swing.
Now, for the interesting part. As your blade goes around, it is vibrating and the sharper your blade is, the less white noise it creates as the teeth attack the wood. Dull blade vibrate at the same pitch as a sharp blade, but has more amplitude like swinging higher in the playground swing. With me so far?
The key thing here is that as the blade vibrates, each tooth does not come around and stride the wood in the same position. You will see this on your work piece as a line where the blade tip encountered the wood. If you lower the feed rate, the blade will tend to cut cleaner. This is because you are putting less white energy into the saw blade and it vibrates with less amplitude. It helps a little but doesn't really solve the problem of a dull blade.
One thing that can help is a stiffer blade. The only way to make a stiffer blade out of steel is to make it thicker or smaller in diameter. Remember the buzz saw with the 3 foot diameter blade. It might have been thick, but it was much bigger in diameter. The Forrest blade is one of the thicker common saw blades that us wood workers use and it cuts cleaner than thin blades given the same sharpness. It does have a down side in that it cuts a wider kerf and takes more feed force and puts too much force on very thin work pieces. It requires more horse power too.
The other thing that happens with a vibrating blade is that it rubs the sides of the kerf more than one that is not vibrating so much. Rubbing causes heating of the blade and warping of the blade. More "set" can compensate for this, but you are still left with the vibration. Notice how saw blades are made with slots cut into the blade from the outer edge toward the center? This is allow space for the outer edge of the blade to expand so as not to accumulate the expansion all the way around the blade causing it to warp. It helps, but does not eliminate the problem.
The myth #1 here is that you can not eliminate saw blade vibration by any of the methods described above like sharper blades, thicker blades, blades made with stronger steel, blades with more set or blades with special teeth or slots. All you can do is minimize the affects of vibration.
When I was a kid, I recall that my uncle heated with wood and that he had a "buzz saw" that he used to cut his wood up into small pieces. If you have ever been around one of these, you know how dangerous it can be. It has a blade at least 3 feet in diameter with big ugly teeth. My uncle's was run off the flywheel on his tractor using a big flat belt, so you know that it had a lot of power. The main thing that I remember is the "sound" that the blade made. If you ever heard a "buzz saw" running, I know that you remember that sound. It was a loud ringing sound that could only come from a "buzz saw". Now, you may ask why the sound of a "buzz saw" is such a big deal? I will explain that as part of myth #1.
If you know anything about music, then the following will be easy to follow. I might note, that as part of my woodworking, I make custom classical guitars. Using the guitar as an example, you know that each string has it own sound or vibration frequency. The fat strings are lower pitched and they vibrate slower than the thin strings that are higher pitched and vibrate faster. If you pluck the string softer or hard, the pitch is still the same. If we look at the violin, we don't actually pluck the strings, we run a rosined bow across the strings. What the bow does is to pluck the string millions of times in a random fashion. This we call "white noise" and the string vibrates according to its length and tightness, not how hard or soft you run the bow across the strings. The more of this "white noise" or energy that you put into the violin, the louder that it sounds. The sound gets louder as the string vibrates a greater and greater distance. It is a little like swinging in a playground swing. You might swing just a small amount or very high, but it always takes the same amount of seconds to make one full swing. Are you with me so far? Now back to the saw blade.
Just like the swing or the strings on a guitar or a violin, each saw blade has its own pitch. Remember the "buzz saw"? When you first turn on you table saw, did you notice that you can hear the ringing of the saw blade as it runs? Try different saw blades and you will find that each one vibrates at it own pitch. I know that most of you think that all saw blades do this ringing, but there are some that don't! I will get into that in another blog. Just like the guitar or the violin, the more white energy that you put into the blade the greater the sound and the distance that the blade vibrates, like the swing.
Now, for the interesting part. As your blade goes around, it is vibrating and the sharper your blade is, the less white noise it creates as the teeth attack the wood. Dull blade vibrate at the same pitch as a sharp blade, but has more amplitude like swinging higher in the playground swing. With me so far?
The key thing here is that as the blade vibrates, each tooth does not come around and stride the wood in the same position. You will see this on your work piece as a line where the blade tip encountered the wood. If you lower the feed rate, the blade will tend to cut cleaner. This is because you are putting less white energy into the saw blade and it vibrates with less amplitude. It helps a little but doesn't really solve the problem of a dull blade.
One thing that can help is a stiffer blade. The only way to make a stiffer blade out of steel is to make it thicker or smaller in diameter. Remember the buzz saw with the 3 foot diameter blade. It might have been thick, but it was much bigger in diameter. The Forrest blade is one of the thicker common saw blades that us wood workers use and it cuts cleaner than thin blades given the same sharpness. It does have a down side in that it cuts a wider kerf and takes more feed force and puts too much force on very thin work pieces. It requires more horse power too.
The other thing that happens with a vibrating blade is that it rubs the sides of the kerf more than one that is not vibrating so much. Rubbing causes heating of the blade and warping of the blade. More "set" can compensate for this, but you are still left with the vibration. Notice how saw blades are made with slots cut into the blade from the outer edge toward the center? This is allow space for the outer edge of the blade to expand so as not to accumulate the expansion all the way around the blade causing it to warp. It helps, but does not eliminate the problem.
The myth #1 here is that you can not eliminate saw blade vibration by any of the methods described above like sharper blades, thicker blades, blades made with stronger steel, blades with more set or blades with special teeth or slots. All you can do is minimize the affects of vibration.
