Trim and Cutoff Saws
These saws have light tooth loads and the extreme outside corner of the tooth must cut through the grain fiber without disturbing it any more than necessary. This means that the uniformity of the chip load is very important. If you refer to the section in this manual on facing, you will note that it plays a key role in trim saw performance. Refer to the industrial Saw Blade Section or the Saw Blade Sharpening Index for related articles.
The hook or rake angle must be maintained and a uniform amount of carbide removed from the face of each tooth.
A good rule of thumb is to try and maintain at least 95% efficiency of the saw. If a saw has 100 teeth, no more than 5 teeth can be out of the cut due to broken teeth or irregular grinding. These must be staggered around the saw. If the corner teeth have very small corner breaks, these teeth will probably come back into the cut after the saw has been sharpened once or twice. If you don't want these small nicked teeth to show, they can be ground down on the top until the nick is gone. They will still come back into the cut after additional sharpenings.
Of course, the very best way to service is to shoot for 100%. No trim saw should be faced more than twice without going over the sides and tops. Sometimes it is necessary to do the complete job every time the saw is serviced. This is where good judgement and experience comes into play.
Top grinding a trim saw is also very important to the saw's overall performance. In the case of the Alternate Bevel saws, the teeth must be dialed the same height and ground to the same angle. If they are not, the saw will lead off track and cut erratically.
Concentricity is a must. Side Grinding is the most important grinding done on a trim saw. It is the side of the tooth that has to sheer the cross grain fiber. The sides should be finished with a very fine diamond wheel. The better the surface finish on the sides, the better the saw will cut. The sides must also be straight and not dubbed over on the corners.
Rip Saws and Edger Saws
These saws have less teeth than trim saws and also heavier chip loads. The tops of the teeth cut across the grain fiber just like a hand chisel cuts across the grain fiber.
It takes very little additional power for a rip saw to have a .020 chip load than a .040 chip load. The tooth still has to sheer all the way across the top of the tooth, regardless of the tooth load. The sides of rip saw teeth get very little action. They wear themselves dull by rubbing the sides of the cut.
The more hook or rake a rip tooth has, the easier it penetrates the cross grain fiber. The more back clearance on the tooth, the easier the tooth also penetrates.
In the case of carbide; it is necessary to limit the included angle on the tops of the teeth to prevent carbide breackage. Tougher grades of carbide are required on most rip operations, due to shock from heavy chip loads and knots. Face grinding properly is very important and the hook or rake angle must be maintained and the faces not dubbed over on the outer portion of the face. It is also very important that an equal amount of carbide is removed from each face in order to keep the saw in joint and the chip load uniform.
Top grinding is the most important grinding job done on a rip saw. The keener the cutting edge, the easier the saw will penetrate the grain fiber and the less power is required. The finer the surface finish on the tops, the better the overall performance including time between sharpenings.
Side grinding is important as it relates to the finish on the sides of the cut. All teeth must be kept in joint so that deep scratches and revolution marks do not adversely effect the cut quality.
All the teeth in a rip saw must cut uniformly and it is not wise to take any teeth out of the cut. The tooth loads are heavy and the removal of one tooth loads the following tooth far too much for comfort.
Aluminum and Metal Saws
The tooth load on metal saws is light to medium and in the range of .001" to .005". Facing-Topping and Side grinding are all of equal importance since they all play a vital role in the saw's performance.
Facing should be straight and true and a very fine finish is important. The face of the tooth is forming the chip and if it is not smooth, the chip will seize or freeze on the face. Chips that are deposited on the face of the tooth must go around again and attempt to form a chip with the deposited metal instead of the tooth face. Good lubrication helps prevent this chip galling, but a smooth face is also essential.
Top grinding must be done accurately, so the chip load is uniform. The surface finish on the tops should be very smooth so that a very sharp corner enters the cut and not a ragged edge caused by rough grinding.
Side grinding is of equal importance in order to obtain a smooth cut on the sides of the cut. Here again, the smoother the surface finish, the better the cut.The two most important operations in servicing a carbide saw are:
#1 - accuracy
# 2 - the surface finish on the carbide. You just can't compromise and expect consistent results.
Article by Lowell Freeborn
