First, the composition of the saw chain. The saw chain is made up of left and right teeth, middle guide teeth (also called driving teeth) connecting piece, and rivets. Second, the model of the saw chain, the size of the saw chain The saw chain is represented by Latin letters and Arabic numerals. Due to the country of manufacture and the manufacturer, the meaning of each letter and number is different, but the pitches, thickness of the guide teeth, shape of the incisors, and safety , Abrasion and other variations of the characteristic symbols. The pitch is the center distance between the two teeth of the cutting tooth and the middle guide tooth. On the same type of saw chain, their pitch (hole distance) is the same, and they are all expressed in inch inches. The measuring tools we use are all metric, and they must be converted when measuring. 1 inch = 25.4 millimeters. If you want to calculate the metric size, multiply it by 25.4. Example B3L, pitch: 25.4 × 0.404 mm; thickness of middle guide teeth: 25.4 × 0.063 mm. Third, the matching of the saw chain Whether the saw chain and 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 groove. The pitch of the saw chain must be the same as that of the sprocket and the gear of the guide plate (if toothed ) Keep the same. The thickness of the middle guide teeth should be consistent with the guide groove on the guide plate, and the length must be consistent with the guide plate circumference, the number of sprocket teeth, and the space distance between the sprocket and the guide plate. Fourth, the length of the saw chain Take the B3 saw chain used for 18 inches as an example, the saw chain used is riveted into a circular ring, there are 30 left and right incisors, and the pitch between each two incisors is 4 pitches (the upper pitch of the incisors is also counted), 0.404 × 4 × 30 = 48.48 (inches) 1 foot = 12 inches, divided by 12 inches, 48.48 ÷ 12 = 4.04 feet, the length of this saw chain is 4.04 feet. (Calculated using the middle guide tooth is multiplied by 2) The length of each box is 100 feet. The pitch of each type of saw chain is different, so the number of cutting teeth is different. The guide teeth in the connecting piece attached to each cutting tooth have a total of 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 (cut teeth) K type: 100 (feet) ÷ (0.325 × 4 ÷ 12) = generally 924 (cut teeth) Type N: 100 (feet) ÷ (0.365 × 4 ÷ 12) = generally 822 (cut teeth) A normal saw chain should be paired left and right to prevent cutting deviation, that is, symmetrical, even number of cutting teeth. The 100 feet issued by the manufacturer are not exactly integers, and some are for the given saw. Chain incisors are even. However, some guide plates are not standard. The riveted saw chain teeth must be odd. Two left (or right) teeth are on one side, and the connecting piece and middle guide teeth are added. Then its total length is calculated by the middle guide teeth. There is two pitches between every two guide teeth (the pitch on the middle guide teeth is also counted), then its length is the pitch multiplied by 2 and the number of the middle guide teeth is divided by 12. Take a K-shaped chain with 59 guide teeth as an example: 0.325 × 2 × 59 ÷ 12 = 3.196 feet. The calculation method of other types of saw chains is the same, the difference is their pitch.