Tech Talk
What are the "Uses of Band Saws"?
There was a time when band saws were an integral part of every woodworking plant or shop. They were used for roughing out shapes that were drawn or traced on a piece of solid wood. From the band saw, the material was sent to the router, shaper or sander for finishing. In frame shops, however, the part usually went directly to assembly. A good band saw operator was a big asset. He new exactly how hard and fast to feed the material in order to get the most production out of each blade - and he could tell in seconds the quality and condition of the blade. Today, for a large part, the band saw has been replaced by CNC routers, eliminating, with automation, one step in the manufacturing process. However, custom shops, small plants and frame manufacturers still use band saws extensively, as do most large plants for short runs and samples. Band saws are mostly used to shape but they can, however, also be used to resaw or rip solid wood. There are basically three things to consider when assessing your band saw requirements - width, tooth pitch, and material. The width is determined by the type of cut. If it is straight line ripping, a 3/4" blade has the beam strength to cut straight. If the job requires shaping and turning, determine the smallest radius in the pattern and order the blade width that will handle that radius. For the best performance and longest blade life, always order the widest blade that will do the job. If you try to cut with a blade that is too wide for the radius, the result will be burning, rough finish, poor blade life and possibly broken blades. Tooth pitch is determined by the thickness, type of material being cut, the required finish, and the speed at which you want to cut. The range for wood cutting is from 3/4" tooth spacing (or pitch) to 14 TPI (teeth per inch), with most shaping done with blades having from 3 to 6 TPI. Generally you use fewer TPI for thicker material and more for a better finish. For example, roughing a piece of 4/4 maple with a large radius (from 2?1/2" up) the blade to use would be a 1/2" x 3 TPI. If you were after a better finish, or the material was much thinner, 4 or even 6 TPI could be used, but cutting time will be sacrificed. As you get to smaller blades (3/16" and under) the tooth pitch becomes smaller because the blades don't have enough body to be strong enough for the relatively big bite of a large tooth pitch. Only the tips are hardened, so that the body of the blade remains soft enough to handle the constant flexing as the blade goes around the wheels. Hard back band saw blades, with tempered or hardened backs for better tracking, are available, but they are generally used at slow speeds for cutting metals. Because of the higher speeds required in cutting wood, they would tend to crack and break. The standard gauge for narrow bands (under 3/4") is 0.025", but for use on three?wheeled or small?wheeled machines, blades as thin as 0.014" are available. Also available are heavy gauge (0.032") blades which work well on wetter or tougher materials. For example, they work well cutting plywood. Band saw blades are available carbide tipped, but we usually only recommend these for exotic woods, MDF or particle board. Bimetal blades have high speed (M2) steel tooth tips and are sometimes used for wood, although they are specifically made for metal cutting. They will last longer than regular bands, but rarely do they justify the price difference (as much as 3 to 4 times) in footage cut when used on wood. If band saw blades are to give their best performance, mounting and setting them in the guides is critical. After the blade is in place it should be "free wheeled" by spinning the blade by hand. During this free wheeling, the blade should not touch the side or rear guides. There should be about 1/64" clearance all round. The guide bearings must be free, with no sticky or hard spots, and not be cut or grooved on the surface. If there are guide blocks, they should be even and square. All of this applies to the bottom guides as well. When you are ready to cut, set the top guide close to the height of the work piece for maximum blade support. If the wheels are running true, the tires are in good shape, and the blade is properly tensioned - with the right blade there should be no problem getting clean, accurate cuts and full blade life.
by: Doug Reid, President, B.C. Saw
