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Assembly of gears, worms, and worm gears 1. Before assembly, it is necessary to familiarize oneself with the equipment’s technical documents in order to understand the installation location, rotation direction, speed, and lubrication method. 2. The following checks should be carried out before assembly: ⑴ The module, outer diameter, and pitch circle diameter of the gear (or worm gear) ； ⑵The fit between the hole of the gear (or worm gear) and the shaft, and the fit between the key and the keyway ； ⑶If any deviations are found in the distance between the driving shaft and the driven shaft, or in their parallelism or perpendicularity (especially in herringbone gears), it is necessary to have the relevant department address these issues before assembly can proceed ； 3. When the gear (or worm gear) is mounted on the shaft, its radial runout and end face runout should be checked. During inspection, the gear, as well as the dial indicator and micrometer, are fixed to a bracket, and the gear is rotated to measure its deviation. 4. After each pair of gears is assembled, the assembly clearance and contact condition should be checked using the following methods. ⑴Use a feeler gauge to check the lateral clearance when the two teeth are in contact. Turn the pinion to one side so that the two gears are in close contact, and then use the feeler gauge to measure the gap between the areas where the teeth are not in contact ； When checking the top clearance, it should be done after aligning one tooth tip with another tooth root. The side clearance should meet the requirements in the following table: Side clearance of spur gears (mm), Precision grade, Module, Center distance between the two gears (mm): Below 300, 300–500, 500–1000, 1000–1600, 1600–2400, Above 2400; Minimum, Maximum values for each range are as follows: Grade II: ≤10, 0.10, 0.50, 0.15, 0.60, 0.20, 0.75, 0.30, 0.80; >10: 1.17, 0.35, 1.00, 1.50, 0.15, 0.70, 0.20, 0.90, 0.25, 1.10, 1.30, 0.40, 1.60. Grade III: ≤10, 0.15, 0.70, 0.20, 0.90, 0.25, 1.20, 0.30, 1.50; 10–24: 0.20, 1.00, 0.25, 1.20, 0.30, 1.45, 0.40, 1.60, 0.50, 2.00; >24: 2.70, 0.30, 1.45, 0.40, 1.70, 0.50, 2.00, 0.60, 2.30, 0.70, 2.20. Grade IV: ≤24, 0.30, 2.00, 0.40, 2.20, 0.50, 2.60, 0.60, 3.00, 0.80, 2.90, 1.00, 4.00; 0.70, 3.30, 0.90, 3.80, 1.20, 4.40, 1.45, 5.20; >24: 1.40. The top clearance of spur gears can be calculated using the following formula if no specific value is specified: C = 0.20m – 0.25m. ------------------------------------------------------------------------------------ (26) C represents the top clearance in mm, while m represents the module of that gear. ⑵When using the lead compression method to check the end play and side play of gears, the length of the lead wire should be at least 5 tooth pitches; its diameter should not exceed 3 times the end play. One lead wire is placed at each end of the tooth surface, with grease applied to that surface. For gears with a larger tooth width, at least 2 lead wires should be placed evenly along the direction of the tooth width. After rotating the two gears, the compressed lead wires are removed, and a micrometer is used to measure the thickness of those wires. ⑶To check the meshing clearance using a feeler gauge or the lead compression method, measurements should be taken at 0°, 90°, 180°, and 270° around the gear. ⑷The contact surface of gears is inspected using the coloring method, and the percentage of contact spots should meet the values shown in the table below: Percentage of Contact Spots, Gear Type, Precision Grade, Measurement Location: 3, 4, 5, 6, 7, 8, 9, 10, 11. The percentage of contact spots should not be less than the following values: For spur gears (involute tooth profile), tooth height: 55, 60, 55, 50, 45, 40, 30, 25, 20; tooth length: 95, 90, 80, 70, 60, 50, 40, 30, 25. For spur gears (circular arc tooth profile), tooth height: 70, 65, 60, 50; tooth length: 90, 85, 80, 75. For bevel gears, tooth height: 75, 70, 60, 50, 40, 30, 30; tooth length: 75, 70, 60, 50, 40, 30, 30. For cylindrical worms, tooth height: 60, 60, 60, 50; tooth length: 75, 75, 75, 60. The tooth height is also 60, 60, 60, 50 for other cases; tooth length is 70, 70, 65, 50, 35 in those cases. Before assembling the worm gear with the worm, it is necessary to check that their pressure angles are identical and that the gears rotate smoothly. Worm gears and worms are usually already mounted on the shafts at the time of manufacture; if assembly is to be done later, the fit between the worm gear and the shaft, as well as between the worm and the shaft, is of the interference type, meaning that the shaft is 0.10–0.04 mm larger than the hole. 6. The longitudinal centers of the worm gear and the worm should be perpendicular to each other. The allowable deviation in their rotational center distance shall be in accordance with the provisions in the design or equipment technical documents; if no such provisions exist, inspection shall be carried out as specified in the table below. Deviation of the rotational center distance of the worm gear pair (μm), Rotational center distance a (mm), Precision grade: 1 2 3 4 5 6 7 8 9 19 11 12. a ≤ 30: 3 5 7 11 17 26 42 65; 30 < a ≤ 50: 3.5 6 8 13 20 31 50 80; 50 < a ≤ 90: 4 7 10 15 23 37 60 90; 90 < a ≤ 120: 5 8 11 18 27 44 70 110; 120 < a ≤ 180: 6 9 13 20 32 50 80 125; 180 < a ≤ 250: 7 10 15 23 36 58 92 145; 250 < a ≤ 315: 8 12 16 26 40 65 105 160; 315 < a ≤ 400: 9 13 18 28 45 70 115 180; 400 < a ≤ 500: 10 14 20 32 50 78 125 200; 500 < a ≤ 630: 11 15 22 35 55 87 140 220; 630 < a ≤ 800: 13 18 25 40 62 100 160 250; 800 < a ≤ 1000: 15 20 28 45 70 115 180 280; 1000 < a ≤ 1250: 17 23 33 52 82 130 210 330. The lateral clearance between the worm gear and the worm is generally 0.30–0.65 mm, while the end clearance should depend on the position of the worm gear and the worm ； If the worm is on top and the worm gear is at the bottom, the clearance at the top must be no less than 1 mm ； If the worm is at the bottom and the worm gear is at the top, its clearance at the top must not be less than the clearance of the bearing shells. The meshing clearance between the worm and the worm gear can be checked and adjusted according to the table below. Meshing clearance between worm gear and worm (mm): Center distance (a) ≤40: 0.055; 40＜a≤80: 0.095; 80＜a≤160: 0.130; 160＜a≤320: 0.190; 320＜a≤630: 0.260; 630＜a≤1250: 0.380; 1250＜a: 0.530. 8. For the assembly of bevel gears, it is necessary to first align the centerlines of the two shafts in the same plane. Adjust the gear clearance first, and then adjust the axial play of the shafts; use a feeler gauge for inspection, with the allowable deviations specified in the table below. When the gears rotate and mesh, there should be no grinding noise or abnormal sounds. Side clearance of bevel gears, transmission accuracy grade, module, side clearance (mm): minimum, maximum. Grade III: below 5 – 0.20, 0.75; 5–10 – 0.25, 0.80–0.85; above 10 – 0.30, 0.90. Grade IV: below 10 – 0.30, 1.10; 10–16 – 0.40, 1.20; above 16 – 0.50, 1.40. When checking the coloring of the contact surface of bevel gears, the shaft must not move during rotation. Under no-load conditions, its contact surface should be 2~4 mm away from the edge of the gear’s small end, tilted toward that end; the contact area should account for 30%~35% of the gear’s working area, with contact occurring along the middle part of the tooth height ； However, due to the slight displacement caused by load torsion, the actual contact area is shown in the figure. 10. When using the coloring method to inspect the meshing contact spots of drive gears, the following requirements shall be met: (1) Apply color to the pinion (driving gear) or worm, and under light braking, use the pinion to drive the gear, causing it to rotate 3–4 times ； ⑵The contact patch of cylindrical gears and worm gears should be located near the middle of the tooth flank, while the contact patch of bevel gears should be near the middle of the tooth flank as well, but closer to the smaller end. For reversible gear drives, both sides should be inspected ； ⑶The percentage value of the contact spot is calculated using formulas 27 and 28: Percentage in the direction of tooth length = (a – c) / B × 100% ------------------------------------------------------------27 Percentage in the direction of tooth height = hp / hg × 100% ------------------------------------------------------------------28 Where: a – Distance between the poles of the contact mark, in mm; c – Distance of separation beyond the module value, in mm; B – Total length of the tooth, in mm; hp – Average height of the contact mark (for spur gears and worm gears) or the height at the middle of the tooth-length contact mark (for bevel gears), in mm; hg – Working height of the tooth (for spur gears and worm gears), in mm ； or corresponding to the effective tooth height at hp (for bevel gears), mm