Modulus: The graduation circle of a gear is the benchmark for designing and calculating the dimensions of all parts of the gear. The circumference of the graduation circle is =πd=z p, so the diameter of the graduation circle is d=z p/π 1. For radial control gears, some countries regard the radial pitch as the basic parameter of gears with different modules, and the measurement unit is inches. The radial pitch is expressed by P, and P refers to the number of teeth per inch on the graduation circle. Radial pitch P=Z/d (d is in inches) and modulus m=d/Z (d is in millimeters). Therefore, the relationship between modulus m and radial pitch p is reciprocal, but the unit system is different. M =1/p * 25.4p =1/m * 25.4 The product of modulus and pitch is always equal to 25.4. 2. Dual-mode number system: Dual-mode number system is another way to obtain short tooth profile, which can improve bending strength, but has poor stability, and is often used in automobile and tractor industries. The dual-mode number system stipulates that the dimensions of each part of a gear are calculated with two modules with different sizes, marked as fractional form m 1/m2, in which the larger module m 1 is used to calculate the diameter of the indexing circle and the smaller m2 is used to calculate the gear tooth size. The calculation formula of each dimension is as follows: diameter of indexing circle: d=m 1*Z tooth top height: ha=ha*m2 tooth root height: hf=(ha 1+c 1)*m2 tooth top circle diameter: da = d+2 * ha = m/kloc-0. Indexing tooth thickness s, pitch p, base circle diameter db and center distance a3. Double diameter constraint: Double diameter constraint is another method to obtain short tooth profile in English gear to improve bending strength. It stipulates that the diameter of the dividing circle is calculated with a smaller pitch P2, and the gear tooth size is calculated with a larger pitch P 1, which is marked as P2/P 1. The smaller pitch P2 is the numerator and the larger pitch P 1 is the denominator, which is just the opposite of the dual-mode number system. The calculation formula of each dimension is as follows: diameter of indexing circle: d=Z/P2; tooth top height: ha=ha/P 1 tooth root height: HF = (ha1+c1)/p1tooth top circle diameter: da = d+2 * ha = z/p2 (ha1+c1)/p1In addition, the tooth thickness s, tooth pitch p, base circle diameter db and center distance a of the indexing circle are all calculated according to P2. 4. Therefore, the pitch of 10/20 is the symbol of the double-diameter control gear (P2/P 1). This means that the smaller pitch P2= 10 (numerator) is used to calculate the diameter of the indexing circle, and the larger pitch P 1=20 (denominator) is used to calculate the tooth height. Therefore, the dimensions of the double-diameter control gear with the pitch of 10/20 are calculated as follows: the diameter of the indexing circle: d=Z/P2=Z/ 10 (d is in inches); Height of tooth tip: ha = ha/p1=1/20 = 0.05 "= 655. P1=1.25/20 = 0.625 "=1.588 mm center-to-center distance a is calculated as smaller diameter section 10. It is also possible to convert the double-diameter control into the dual-mode number system first, and then calculate the size: the dual-mode number system is marked as fractional form m 1/m2, the large modulus m 1 is used to calculate the diameter of the indexing circle, and the smaller m2 is used to calculate the gear tooth size. m 1 = 1/P2 * 25.4 = 1/ 10 " * 25.4 = 2.54 mm2 = 1/p 1 * 25.4 = 1/20。 This gear is represented by a dual-mode digital gear, which is 2.54/ 1.27: size calculation: diameter of indexing circle: d=2.54*z tooth top height: ha = ha * m2 =1.27 =1.27mm tooth root height: HF = (.