It's all in the tooth shape with High Speed Steel Circular Saws....

by THE SAW DOCTOR

A High Speed Steel Circular Saw is also commonly known as a Cold saw or Brobo.
 
The most common problem that I come across with HSS Circular Saws is an incorrect tooth shape.

The tooth shape determines whether the blade is a good sharpen or a bad sharpen. The saw can be sharpened on the latest CNC machine, but this does not mean you are guaranteed a perfect sharpen. If the operator of the sharpening machine does not select the correct width grinding wheel and tooth geometry this can alter the cutting results of the blade dramatically.  The teeth can be as sharp as they like, but if the tooth shape is not correct this will make the blade feel as though it is blunt as soon as you put it on your machine.

If the gullets are too narrow this does not allow the swarf to curl and fall out of the teeth, instead the swarf stays in the teeth clogging the tooth gullets not allowing the teeth to bite into the steel. When the gullets are too narrow this also causes the teeth to break out. This is due to the stresses that the teeth are under, to relieve this stress on the tooth it then breaks off which can also lead to the blade cracking or breaking a section out of the blade.

Diagram 1



You may have experienced this when you have purchased a new blade, you put the blade on your machine, do a couple of cuts and the blade feels blunt, that’s because the wrong grinding wheel thickness and tooth geometry were applied when toothing the blade. That’s why I only buy the saw blades as blanks and tooth the blades myself to ensure that the correct tooth geometries are applied for the perfect tooth shape.
 
A correctly sharpened HSS Circular saw has a rounded gullet and the gullet size is half the pitch of the teeth. The reason for this is to allow the swarf to curl and then exit the cut. Allowing the gullets to be free of swarf makes sure that the teeth are able to bite into the steel and give you optimum cutting results.

Diagram 2



In the diagram below you can see how much larger the tooth gullets are compared to Diagram 1. Also notice how the gullets have a round shape to it as this ensures a perfect curled chip as I mentioned before.
 
Diagram 3



The same saw blade has been used for both Diagram 1 & 3, one before I sharpened it and one after I sharpened it. The two different tooth shapes give two very different cutting performances.

To have the perfect tooth shape the tooth geometry has to be applied. By applying the geometry formulas ensures you are getting the best sharpen and cuttings results. This then enables you to complete your jobs more efficiently.
 
Until next time.......... Happy Cutting!

 

October 9, 2012
 

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