by Lowell Freeborn

Saw gumming is an operation that must be performed on all saws to be retipped.  It must be done accurately so the saw does not run out of balance and the tip recesses are all the same depth.  The job can best be accomplished by using a gear index fixture where the gears can be changed for different tooth quantities.  Using this method, the indexing is done by finger indexing into the gear teeth, which leaves the tooth area open on the saw and allows all the freedom you need in gumming.  Also see our articles on Grinding Saw Blades or browse for other saw blade articles in the Saw Blade Index. 

The first thing to do is to draw your hook line on the saw with a pencil. This can be easily done by the use of a standard drawing instrument used on drawing boards.  First draw a center line to the tip of the tooth you start with, then draw a line from the same point at the desired hook angle.  Now line up the hook line with the side of the wheel and you are ready to-gum the saw. 

Layout of Hook Line 

Do not grind so fast that the saw gets hot and turns color.  This will cause a surface hardening of the steel and could be a cause of cracking.  In order to keep the wheel from burning it is sometimes advisable to bounce it several times as you grind.  This will help rough it and keep the wheel from glazing as well as allow the stock to cool a little. 

Several sizes of wheels are necessary to get the job done quickly and to gum the various shapes of teeth required. 

These wheels can be dressed by using a dressing stick or a rotary wheel dresser.  The latter is best. 

Gumming also includes recessing for carbide tips.  This operation must be done with precision.  To accomplish this it is best to use a spring type locating finger that will index in the opening just below the tip recess.  The best procedure is to use a 1/8" cutoff wheel and rough in the recesses before finishing them to the proper depth.  Then dress the wheel square and proceed to gun the recesses to their finished depth.  After going around once, it may be necessary to dress the wheel square and go around again. The corner of the wheel will break down and you must have a seat for the tip that it will fit in properly and not hang up on a large corner radius caused by excessive corner break down of the wheel. 

1. Do not install a broken wheel. Be sure that you ring it to check for possible cracks.
2. Be sure to wear eye protection.
3. All gumming machines should be equipped with a wraparound shield to protect the eyes of people in the vicinity of the machine.
4. Gumming is one of the most important operations performed on a saw, so do it right.