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TOOTH SHAPE

The choice of tooth shape or design is normally based upon two factors:

  1. Temperature of the stock or work piece
  2. Dimensions of the cross-section being sawed

In hot sawing, a V-type tooth, usually symmetrical, is the most common so that the blade can cut in either direction, with an included angle of 55-60 degrees. This provides a balance between heat absorption, gullet space and cutting forces. (The greater the angle, the more negative the rake, and more power is needed to remove the chip.)

When the temperature is high, (1800 F / 980 C or higher), a simple V is used. When temperatures fall below this, a small flat or land is added to the top of the teeth. Generally, the lower the temperature, the larger the flat.

In friction sawing, it is necessary to add heat to soften and melt the workpiece material. This is achieved using a substantial flat (see tooth C). The size of the flat or land varies depending on the section being sawed. As the wall or section increases, it is desirable to increase the size of the flat to create more frictional heat. Typically, the flat may vary from about 20% of the pitch for thinner wall to a maximum of 40% for thicker wall. Above 40%, feed forces become too high and restrict chip space in the gullet. Then, saw chips cannot be removed by high pressure-water jets and tooth clogging occurs.

When sawing lighter gauge tubes and thin sections where deformation of the cross section is a problem, it is necessary to use a tooth shape that- minimizes the cutting forces, such as radial or promo shapes. Such saw blades are commonly called tube saws whether the operation is hot or cold. Where some frictional heat is needed, a small flat can be added.

Rake angle is sometimes varied to achieve better results. Larger rake angles (e.g. positive) produce lower forces but smaller included tooth angles and therefore lower heat capacity. Smaller rake angles (e.g. negative) increase heat capacity and increase heat generated in shearing but increase cutting forces.

Whatever tooth form is used, a generous radius in the bottom of the gullet is necessary to minimize stress concentration and therefore cracking. A minimum of 20% of the pitch is suggested.

For further information or assistance, please contact ASKO.

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