The saw chain is an indispensable part of the chain saw. Without the chain, the chain saw cannot work and cannot be called a saw. It's just an engine, but there are many people who don't know much about saw chains. Let me give you a brief introduction.

1. The composition of the saw chain
The saw chain is composed of left cutting teeth, right cutting teeth, middle guide teeth (also called driving teeth) connecting pieces, and rivets.

2. The model of the saw chain and the size of the saw chain
The saw chain is represented by Latin letters and Arabic numerals. Due to different countries and manufacturers, the meanings of each letter and number are different, but what they indicate are the pitch, the thickness of the middle guide tooth, the shape of the cutting tooth, and for safety , Reduce wear and other characteristic symbols of variation.

The pitch is the center distance between the cutting teeth, the middle guide teeth, and the two holes of the connecting piece. On the same type of saw chain, their pitch (hole distance) is the same, and all are expressed in inches in English. The measuring tools we use are all in metric system and must be converted when measuring. 1 inch = 25.4 mm, if you want to calculate the metric size, multiply 25.4 and the size it represents. Example B3L, pitch: 25.4×0.404 mm; thickness of middle guide tooth: 25.4×0.063 mm.

Third, the matching of the saw chain
Whether the saw chain and the chain saw match, mainly depends on the chain wheel of the chain saw, the length of the guide plate, the form of the guide plate and the width of the guide plate guide groove, the pitch of the saw chain must be the same as the sprocket, the gear of the guide plate head (if it is toothed ) Keep the same, the thickness of the middle guide tooth is consistent with the guide groove on the guide plate, and the length is consistent with the circumference of the guide plate, the number of sprocket teeth and the spatial distance between the sprocket and the guide plate.

Fourth, the length of the saw chain
Take the 18-inch B3 saw chain as an example. The saw chain used is riveted into a circular ring. There are 30 left and right cutting teeth. There are 4 pitches between each two cutting teeth (the pitch of the cutting teeth is also counted), 0.404×4×30= 48.48 (inches) 1 foot = 12 inches, the data obtained is divided by 12 inches, 48.48 ÷ 12 = 4.04 feet, the length of this saw chain is 4.04 feet. (Multiply 2 for calculation with center guide tooth)
Each box of saw chain is 100 feet long. Different types of saw chains have different pitches, so the number of cutting teeth is different. The guide teeth in the connecting piece attached to each cutting tooth have 4 pitches. The calculation formula and data are as follows:
Type A: 100 (feet)÷(0.375×4÷12)=800
Type B: 100 (feet) ÷ (0.404 × 4 ÷ 12) = generally 744 (tooth cutting)
Type K: 100 (feet) ÷ (0.325×4÷12) = generally 924 (tooth cutting)
Type N: 100 (feet) ÷ (0.365×4÷12) = generally 822 (tooth cutting)
A normal saw chain, in order to prevent cutting deviation, should be left and right in pairs, that is, symmetrical, the number of cutting teeth is even. The 100 feet issued by the manufacturer is not just an integer, and some are a little more for the given saw. The chain cutting teeth are even numbers. However, some guide plates are not standard, the riveted saw chain cutting teeth must be odd numbers, two left (or right) cutting teeth on one side, plus the connecting piece and the middle guide tooth, then its total length is calculated by the middle guide tooth , There are two pitches for every two middle guide teeth (the pitch on the middle guide teeth is also counted), then its length is the pitch multiplied by 2, multiplied by the number of middle guide teeth, and then divided by 12. Take K-chain, the number of guide teeth is 59 as an example:
0.325×2×59÷12=3.196 feet. The calculation method for other types of saw chains is the same, the difference is their pitch.
In addition, there are two data to remember: 1 foot = 12 inches, 1 inch = 25.4 mm

Five, the repair file of the saw chain
The left and right cutting teeth on the saw chain are cutting tools. After a period of use, the cutting edge becomes blunt. To cut smoothly and keep the cutting edge sharp, it is necessary to file.
Note for file repair:
1. Choose a round file suitable for repairing saw chains. The cutting teeth, size, and arc of various types of saw chains are different. Each type of chain requires a certain round file standard. There are detailed instructions in the manual, and you must pay attention to it.
2. Pay attention to the direction and angle of the file. The file should be repaired in the direction of the cutting edge. When pulling back, it should be light. Do not use force back and forth as much as possible. Generally, the angle of the saw chain edge is about 30 degrees, and the front is high and the back is low. The included angle is about 10 degrees. These angles vary according to the hardness of the material being sawed and the use habits of the saw. At the same time, pay attention to the symmetry of the left and right cutting teeth. If the deviation is too large, the saw will run off and saw.
3. Pay attention to the height of the limit tooth. A part of the front of each cutting tooth protrudes, this is the limit tooth, which is 0.6---0.8 mm lower than the upper edge of the cutting edge, and the cutting amount per tooth is so thick. When filing the cutting edge, pay attention to its height , If the cutting edge is repaired more, the limit tooth relative to the cutting edge will become higher, and the cutting amount will be smaller each time, which will affect the cutting speed. If the cutting edge is lower than the limit tooth, it will produce no wood , Unable to cut, the limit tooth repair file is too low, and each tooth is too thick each time, it is likely to cause the "knife" and the saw will not move.

Six, maintenance of the saw chain
The saw chain runs fast. Taking a 3/8 saw chain as an example, the number of sprocket teeth is 7 teeth, and when the engine revolutions per minute during operation, the saw chain runs at 15.56 meters per second. The driving force of the sprocket and the reaction force during cutting are concentrated on the rivet shaft. The working conditions are bad and the wear is serious. If you do not pay attention to maintenance, the saw chain will be quickly scrapped.