Screaming Saw Blades
Screaming Saw Blades
Saw blades are like tuning forks, xylophone keys, bells or any other tensioned piece of metal. They all have a particular frequency at which they resonate. When you hit that particular frequency they make noise.
We you hit the bell with the clapper or a xylophone key with a hammer it resonates and makes noise. It makes a particular noise based on several different factors. The same thing is true with a saw blade but the force is applied in a different manner. When the machine vibration is right, the saw blade starts to vibrate and makes noise. The machine and the saw blade have to be tuned to the same frequency, whether deliberately or accidentally.
Ryszard Szymani of the Wood Machining Institute used to show the video during some of his training sessions. In this video he demonstrated “critical speed” which is another aspect of tuning.
A saw blade starts out from a dead stop and comes up to speed. Depending how fast the saw blade is run it can hit a critical speed where the saw blade wobbles. If the speed of the saw blade continues to increase it will get past the critical speed area and the saw blade will then run straight and true until it hits the second critical speed area. At the second critical speed area the saw blade wobbles two ways so that it looks like a potato chip in slow motion. Again, if you continue to increase the speed and the saw blade will straighten out and run true.
Now this is generally, but not always, described as screaming, singing, or humming. Whistling is generally, but not always, wind such as wind past or through the expansion slots, wind between the saw blade and a zero clearance insert or something similar.
Of course sound is air movement and wind is air movement. Language here can get pretty confused. If you have a different explanation or nomenclature use, I would really appreciate hearing it. However, I won’t argue with you. I will just add it to things I’ve learned.
There are many ways of dealing with this kind of noise. Anything that changes the frequency of the saw blade or the machine will help if it is a harmonic situation and not a whistling situation.
Tony Pense of Superior Saw in Tacoma Washington recommends replacing a cheap blade as it is generally not worth the money to try and change it. With an expensive blade, his first technique is to round the backs, non-cutting part, of the saw tips as this removes a sharp edge and replaces it with a rounded edge. He also suggests making sure that expansion holes are plugged with copper plugs. You can fill expansion slots with an epoxy without affecting saw performance. (Steve Bergerson of Western Saw did a study where he shows that you can reduce saw noise by about 10 dB with the proper expansion slots and epoxy filling. He did these studies on saws that made a normal amount of noise.) You can also take the saw blade to a good saw shop and have it hammered to change the tension. However you’re asking a highly skilled craftsman to work on your saw blade so you want to make sure that it wouldn’t be just cheaper to replace the saw blade.
Everyone who makes saw blades is well aware of the problems a screaming saw blade can cause and saw blades are engineered to be as quiet as possible given the applications and the price point at which they are so sold. However every saw blade is slightly different from every other sawblades and every machine is slightly different from every other machine so occasionally a combination will come together where the saw blade screams.
I can’t remember if we have ever sold a saw blade that screamed. (Now that I have said that, I’m sure that we will sell at least two of them tomorrow just because I opened my big mouth.)
If we should ever sell a saw blade that screamed we would replace it with a new saw blade. It is really the simplest, cheapest and fastest way to solve the problem. You could probably replace it with the same blade from the same manufacturer and eliminate the problem. The customer would probably be happier with an equivalent blade from a different manufacturer.
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