The Three-Tooth Rule, or How the Number of Teeth Work in a Cut. In order to obtain the best TPI (teeth per inch) for the smoothest cut, follow the three-tooth rule.
A minimum of three and a maximum of 24 teeth engaged in a cut.
If there are too few teeth in a cut, the blade’s teeth can straddle the work piece and cause the teeth to strip.
Too many teeth in a cut may cause the gullets to overload due to there not being enough gullet capacity to hold all of the chips.
Along with having teeth strip from the saw blade, blade bounce is likely to occur as well. Eventually, the bandsaw blade will become dull and work harden, which can get as hard as the cutting edge. Also, there is the potential for chips welding to the blade surface due to overheating.
Any number of other blade-related problems will occur that can cause a crooked cut, slow down production, and lessen the life of the bandsaw blade.
Application of the three-tooth rule
For structural materials, think about what the blade sees — across the top and the bottom: a wide section. Across the side walls: narrow sections.
To calculate total tooth engagement, add the width of both side walls. It should follow a minimum of 3 and a maximum of 24.
To determine the number of teeth in a cut with variable pitch saw blades and a bar stock, use the average of the pitch and multiply it by the bar stock size.
Consider the following when selecting tooth pitch
- Soft materials require fewer teeth and more gullet capacity
- Hard materials require more teeth to share in the work
- A smaller gullet area gives extra beam strength
- Constant feed machines use a coarser pitch
- Gravity feed machines typically require a finer pitch
- Production or Blade Life
- For production cutting, use a tooth pitch nearest the coarse end of range
- For good finish or smoother cut surfaces, use finer teeth
- For best blade life, run from the middle to the finer end of the recommended tooth pitch range