Sawblades look simple, but they are really very complicated. This blog will go into white noise a little more.
In an earlier blog, I explained how a violin is based on putting white noise into the strings with the bow. The string vibrates according to its weight, tightness and length. As the person plays, he uses his fingers to change the length of the string and thus the rate of vibration or tone. Now back to our sawblade.
All steel has the same modulus of elasticity and thus high alloy blades vibrate at exactly the same as blades made from cheap steel if they are the same thickness and diameter. If that is the case, what can the manufacturer do to make their blades vibrate less? That is the serious challenge for all of us. The higher the pitch of the vibration, the smaller the distance that the sawblade tip moves while cutting. A thicker blade will vibrate at a higher pitch than a thin blade of equal diameter. That is good, but it takes more force to cut and thus it takes more horse power. It also puts more force on the work piece and the structure of the table saw. It also wastes more wood. As mentioned earlier, a sharper blade with create less white noise and thus the sawblade will still vibrate at the same pitch, but with less movement. The sound will thus be lower. It is like plucking a guitar with less force.
There are other ways to change the vibration pitch and the amplitude. :Active damping" is one way. Think of it this way. You have a person swinging high on a playground swing and you put your hand on the person as they swing toward you. With only a small force, you can prevent the person from swinging higher. They will still swing at the same rate, but not as high. In terms of a sawblade, this means the sharp cutting tip of the sawblade will not move out of position as much, and you will get a smoother cut. There are computerized ways to do this same sort of thing with vibrating bodies. Some expensive cars have a similar system to damp the road vibration even more than mechanical shock absorbers. This same thing can also be done with noise in special head phones. I do not know of any economical "active" electronic dampers for our shop tablesaws, but I am sure they are in the works.
There is another way to "reduce" the natural vibration of objects by the use of "tuned mass dampers". Some of you have had guitars where a string was so out of tune that it sounded very dull when plucked. It is possible for "specific" weights to be attached to the sawblade so that it would "confuse' the natural vibration such that it vibrated in a complex mode with one vibration canceling the other. I know of one company who attached stiffeners to their blade and by pure luck the stiffeners turned out to create a new pattern of vibration that canceled out the original natural vibration of the sawblade.
Another method of reducing the vibration is to attach a material that absorbs the vibrational white energy. Some car engines and some airplane engines have used this concept for years. The way that it is done is to attach a weight to the rotating part with some kind of rubber or elastic material between the weight and the rotating part. The elastic material absorbs the white energy. It would be like hitting an anvil with a steel hammer compared to hitting a piece of wood on the anvil. Hitting the wood would sound with a "hud" and hitting the anvil would "ring" like a bell. Cast iron has some of this same property. That is why cast iron is used to make good tablesaws vs steel plate. Steel plated does not absorb the white noise near as well as cast iron. Aluminum car engines have more vibration than those made form cast iron for this same reason.
The big pay off from sawblades that vibrate less is that the blades can be made thinner, making the white noise less and making cheap tablesaws cut almost as well as the heavy expensive ones. Because the thin blade puts so much less force on the work piece, the thin blade can cut thinner and weaker materials. I have such a blade and can cut strips of Basswood to a thickness of 0.010" from a blank as much as 2" thick. The strips need no sanding and can be used directly for binding on my guitars. With less vibration, there is less rubbing on the sides of the kerf and less heating of the blade which reduces or eliminates heat distortion. I'll have more on thin blades in my next blog.
In an earlier blog, I explained how a violin is based on putting white noise into the strings with the bow. The string vibrates according to its weight, tightness and length. As the person plays, he uses his fingers to change the length of the string and thus the rate of vibration or tone. Now back to our sawblade.
All steel has the same modulus of elasticity and thus high alloy blades vibrate at exactly the same as blades made from cheap steel if they are the same thickness and diameter. If that is the case, what can the manufacturer do to make their blades vibrate less? That is the serious challenge for all of us. The higher the pitch of the vibration, the smaller the distance that the sawblade tip moves while cutting. A thicker blade will vibrate at a higher pitch than a thin blade of equal diameter. That is good, but it takes more force to cut and thus it takes more horse power. It also puts more force on the work piece and the structure of the table saw. It also wastes more wood. As mentioned earlier, a sharper blade with create less white noise and thus the sawblade will still vibrate at the same pitch, but with less movement. The sound will thus be lower. It is like plucking a guitar with less force.
There are other ways to change the vibration pitch and the amplitude. :Active damping" is one way. Think of it this way. You have a person swinging high on a playground swing and you put your hand on the person as they swing toward you. With only a small force, you can prevent the person from swinging higher. They will still swing at the same rate, but not as high. In terms of a sawblade, this means the sharp cutting tip of the sawblade will not move out of position as much, and you will get a smoother cut. There are computerized ways to do this same sort of thing with vibrating bodies. Some expensive cars have a similar system to damp the road vibration even more than mechanical shock absorbers. This same thing can also be done with noise in special head phones. I do not know of any economical "active" electronic dampers for our shop tablesaws, but I am sure they are in the works.
There is another way to "reduce" the natural vibration of objects by the use of "tuned mass dampers". Some of you have had guitars where a string was so out of tune that it sounded very dull when plucked. It is possible for "specific" weights to be attached to the sawblade so that it would "confuse' the natural vibration such that it vibrated in a complex mode with one vibration canceling the other. I know of one company who attached stiffeners to their blade and by pure luck the stiffeners turned out to create a new pattern of vibration that canceled out the original natural vibration of the sawblade.
Another method of reducing the vibration is to attach a material that absorbs the vibrational white energy. Some car engines and some airplane engines have used this concept for years. The way that it is done is to attach a weight to the rotating part with some kind of rubber or elastic material between the weight and the rotating part. The elastic material absorbs the white energy. It would be like hitting an anvil with a steel hammer compared to hitting a piece of wood on the anvil. Hitting the wood would sound with a "hud" and hitting the anvil would "ring" like a bell. Cast iron has some of this same property. That is why cast iron is used to make good tablesaws vs steel plate. Steel plated does not absorb the white noise near as well as cast iron. Aluminum car engines have more vibration than those made form cast iron for this same reason.
The big pay off from sawblades that vibrate less is that the blades can be made thinner, making the white noise less and making cheap tablesaws cut almost as well as the heavy expensive ones. Because the thin blade puts so much less force on the work piece, the thin blade can cut thinner and weaker materials. I have such a blade and can cut strips of Basswood to a thickness of 0.010" from a blank as much as 2" thick. The strips need no sanding and can be used directly for binding on my guitars. With less vibration, there is less rubbing on the sides of the kerf and less heating of the blade which reduces or eliminates heat distortion. I'll have more on thin blades in my next blog.
