Gullet Maintenance On Square Chisel Saw Chain
Many pro saw users, who run square ground chisel saw chain, don't do a good job of maintaining the gullets on their saw chain. Most don't understand why they need to be removed, and what the consequences are to their chain's cutting performance when they don't. The following information explains why they need to be removed and how often.
Gullets form when square ground chisel cutter teeth are sharpened. They don't usually occur with round filing or grinding, because it is easy to remove them during the sharpening process. This is not the case with square ground chisel chain. When a square chisel cutter tooth is sharpened with either a file or a grinder, it is necessary to remove gullet material in another process.
When gullets are allowed to get long, they make it difficult for the sharp cutter to get at the wood. This makes it difficult for the chain to feed. Here is the reason: Every time a cutter tooth is sharpened, it gets shorter. As the tooth becomes shorter, the "set" or the amount the cutter sticks out beyond its chassis is reduced, too. Gullets retain their set and if allowed to get too long, they rub in the cut. also, long gullets impede chip flow.
Right & Wrong Gullets
The graphic below illustrates a square ground cutter tooth at various stages during its working life. In the top-down view, in the "wrong" images, it is easy to see how far the gullet extends. Even at half life, this clearly gets in the way of the cutter tooth's sharp corner from getting a "bite" of wood.
In the "right" images, the gullet has been removed and the corner in the cutter's tooth is the most outward point. These cutter teeth will feed well.
Frequently Asked Questions
The following questions are often asked about gullet maintenance:
Q: What is the best way to remove them?
A: Remove them with a round file or a grinder.
Q: Why can't I grind out the gullets at the same time I am sharpening the tooth?
A: The stone (or file) angle necessary to sharpen square chisel chain makes it impossible to remove the gullet at the same time you sharpen it. If you attempt to do it, you will end up cutting into the chassis above the back rivet hole on the tie strap. Damage to the chassis in this area will weaken the chain and cause it to break. Some grinders are setup to remove more gullets than others, but no grinder is able to remove all the gullet material in the same process as sharpening.
Q: How does the factory sharpen a chain without leaving a gullet?
A: This is a good question and it has a simple answer: The factory sharpens the cutter teeth before they assemble the chain. They don't have to worry about grinding into the tie strap under the cutter because when they grind it, it is not there.
Q: Do the gullets need to be removed after each sharpening?
A: No. Most professional saw operators remove them every three to five sharpenings. It all depends on how much of the cutter tooth is ground off on each sharpening. Whenever the gullet grows beyond an 1/8" it needs to be removed.
Even though this cutter tooth is sharp, it will not cut well until the gullet material is removed. The longest this gullet should ever be is 1/8".