Everyone seems to have their own bandsaw tooth design, incorporating different teeth per inch, hook angles and gullet sizes and shapes. Generally, there are three choices: regular, skip and hook. No matter which of these three is your favorite, all the teeth in an individual band are identical in design (hook, clearance and gullet), with uniform width (or side clearance), projecting evenly and identically on each side (alternately), and with the tips protruding the same amount from the saw body (that is, the blade width is the same for all teeth).
On the other hand, there is one design, called the variable tooth that has both 0 degree hook teeth and hook teeth with variable spacing. It cuts smoothly and moderately fast, but the blade is quite expensive.
Teeth per inch
In general, many bandsaw blades have too many teeth except for fine scroll work. Oftentimes, a preferred design for ripping (that is, cutting with or along the grain) is called a skip tooth. This blade has half (rarely 33 percent) as many teeth as a regular band. Each tooth must therefore do twice as much work, but the horse power required for cutting a piece of lumber is still the same. Chips are larger with little fine dust. I have heard from quite a few old timers that their saw blade worked so much better when they ground off every other tooth (halved the TPI). It is something to consider indeed although the surface would be a bit rougher with aggressive feeding. (Hook tooth blades often give similar performance as the skip tooth.)
The so-called "regular tooth blade" with large TPI (14 is common), zero hook angle, small gullets and slow feeding gives the smoothest surface.
Gullet depth is the distance from the tip of the tooth to the bottom (or back) of the gullet. Technically, this measurement is made perpendicular to the back of the blade and not at an angle. The deeper the gullet, the more sawdust it can hold but the less metal left in the body for tension, which keeps the blade running straight. It is important that the gullet shape and curve be smooth, as sharp corners will concentrate stress and cause cracking and eventual catastrophic breaking of the blade.
The hook angle is the angle between a line drawn perpendicular to the back of the saw and a line parallel to the front edge of the tooth. Large hooks mean skinny, potentially weaker teeth. With a large hook, the tooth will act like a chisel and try to split out the fibers. The larger hook angle blade will try to pull the wood into the blade. Typically, for a dense wood, the wood is too strong for a smaller hook angle, so larger angles are used. The larger the hook, the less energy that will be needed, as wood is weak in splitting strength. Large hook angles are preferred for ripping and resawing. Large hook angle blades tend to follow the grain at times, which can lead to blade wandering.
On the other hand, small hook angles (sometimes they are even negative) mean that there will be more metal for the tooth and that the teeth will act more like a scraper or plow than a chisel. Further, more metal means stronger teeth, which is especially important when cutting dense wood or cutting knotty wood where large density variations exist. Small, zero, and slightly negative angles are preferred for crosscutting. Cuts are usually smoother with smaller hook angles.
What is the correct angle? A common hook is 0 degrees for regular and skip tooth blades. A hook tooth blade may use a hook of 8 to 10 degrees. This hook tooth is popular for dense woods and for really knotty wood.
The back of the tooth is ground away so that the back will not rub against the wood as the saw progresses into the cut. Typically, this angle will be 9 to 12 degrees. The greater the angle is, the less metal in the tooth. However, if clearance is too small, the blade will not feed very well; that is, feed fast enough
The three angles, clearance, hook and sharpness, add up to 90 degrees. The sharpness angle is the angle between the front and back of the tooth. In other words, it is the tooth angle.
The tooth tip must be sharp, no matter what the angle. If the tip is dull, the blade will not cut well and will tend to slip and slide, giving a wavy cut. As teeth dull, the hook angle increases and can cause feeding problems and produce poor quality cuts. Dull saw blades develop more heat, which accelerates further dulling. The rule is to always keep a saw blade sharp.
There are three basic ways to make bandsaw teeth wider than the saw body for sawmill blades.
1) Each tooth can be bent slightly sideways (called setting the teeth), alternating adjacent teeth to the left and right. Setting the teeth is easy, but requires practice, with a good setting tool. Setting tools can be manual (arm-strong) or automatic. This is the most common dry-wood bandsaw blade.
2) The tip of the tooth can be mechanically forced to spread out; this process of widening the tip of the tooth is called swaging (pronounced swedging). Once the tip is swaged, it is then filed or ground to give a uniform size for each tooth, in addition to sharpening the cutting edge.
3) The tip can be formed by "welding" on a different material than the metal used for the body. Carbide tipping is probably the most common material. Other materials include diamond, ceramic or Stellite. Because narrow blades tend to have short lives, it is hard to justify using a special, expensive tip material on them. For longer-lasting blades, tip material modification is often done and can greatly extend the time between sharpening. Once the tooth is tipped, it is then ground to the correct shape with uniform side clearance and correct cutting angles, and then the cutting edge is sharpened.
Bandsaws must be kept free of pitch or other residue build-up. Slight discoloration is OK. Many people use turpentine for softwood blade cleaning. Watch the fire hazard with this or any other cleaning solution. Commercial products are available.
There is no one blade design or tooth shape that will work for everyone. In fact, different designs can work well on the same machine cutting the same species. The key for a bandsaw operator is to experiment to find the blade that works best for the operator's particular machine. Further, be willing to change blades when conditions change.
Finally, remember that the band is traveling at 30 mph. Several hundred teeth go by one point in a second. Be safe. Read safety manuals from saw and blade manufacturers. Learn safe procedures and practice safe operation. Use appropriate safety equipment. Avoid an accident.
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