More saws are literally butchered by facing improperly than by any other grinding operation. In the first place, when a saw is first manufactured it has cutting geometry that is designed to perform a certain way. When a customer buys a saw for a specific purpose and it performs to his satisfaction, it now becomes the responsibility of the sharpener to see to it that it does as good a job after servicing as it did before. This means that there can be no changes made in the original geometry of the saw.
Now getting back to the facing operation. Most saws are ruined by facing when the person doing it is not careful and does not grind the face of the tooth parallel with the back and changes the geometry by dubbing the top part of the face back, thus changing the hook angle of the tooth. See the illustration below.
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The next thing that is too often done wrong is not grinding the same amount off of each tooth face. This causes the saw to lose its joint by making some teeth higher than others and some teeth wider than others. Study the illustrations below. Note how tops of teeth become out of joint when improperly faced.
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Note how sides also vary when saws are improperly faced.
You may say that these drawings are misleading because they are exaggerated to prove a point. The first thing to be aware of is that chip load per tooth on cutoff saws is down in the area of .002 to .004 thousandths of an inch. Now you have but to dial indicate the tops and sides to see what variation any given saw has.
If a saw varies on the top even as much as .002 thousandths the tooth directly behind the low tooth will be loaded that much more than it should be or than the saw was designed for. These variations do not have to be very large before you begin to wonder why an 80 tooth saw is necessary for a job when only 40 teeth are working.
The sides of the saw are also affected in the same way and the performance will fall off rapidly when the saw is merely improperly faced. Be assured that there is no substitute for a job done accurately and consistently right. Most face grinding is performed on a gumming type machine that is a hand operation and completely at the mercy of the operator. This requires the operator to have a good feel for the job and a thorough understanding of its basics. Proper set up to face the saw is very important and should not be done in a slipshod manner. See the illustration below.
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After a diamond facing wheel has been used for a while, it becomes rounded over from extending down beyond the carbide and grinding into the steel below. The steel tends to pull the diamond out of the bond causing this rounded condition. When the wheel gets into this condition it is necessary to compensate or dress the wheel face flat again. Most people do not want to dress away their diamond so they go right on butchering their saws and sending out disgraceful work to their customers. This really opens the door for their competition. Refer to the drawing below.
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If you must relieve the backing behind the diamond in order to do a saw with narrow gullets, you must be very careful. It is far better to buy a narrower diamond wheel with 1/32 inch diamond thickness for doing saws with narrow gullets. A well maintained facing wheel will save a lot of time and do a better job.
Treat the facing of a carbide saw like a highly precision grinding job and try to do it better each time you do it.
