Plastics Gear Design Table 13. Tooth Form Factors Y for Plastics Gears Machinery's Handbook, 31st Edition
608
20-deg Internal Full Depth
14 1 ⁄ 2 -degree Involute or Cycloidal
20-degree Full Depth Involute
20-degree Stub Tooth Involute
Number of Teeth
Pinion 0.327 0.327 0.330 0.330 0.333 0.342 0.349 0.358 0.364 0.371 0.374 0.383 0.393 0.399 0.405 0.415 0.424 0.430 0.437 0.446 0.452 0.462 0.468 0.478
Gear
12 13 14 15 16 17 18 19 20 21 22 24 26 28 30 34 38 43 50 60
0.210 0.220 0.226 0.236 0.242 0.251 0.261 0.273 0.283 0.289 0.292 0.298 0.307 0.314 0.320 0.327 0.336 0.346 0.352 0.358 0.364 0.371 0.377 0.383
0.245 0.261 0.276 0.289 0.259 0.302 0.308 0.314 0.320 0.327 0.330 0.336 0.346 0.352 0.358 0.371 0.383 0.396 0.480 0.421 0.434 0.446 0.459 0.471
0.311 0.324 0.339 0.348 0.361 0.367 0.377 0.386 0.393 0.399 0.405 0.415 0.424 0.430 0.437 0.446 0.456 0.462 0.474 0.484 0.496 0.506 0.518 0.534
… … … … … … … … … … … … …
0.691 0.679 0.660 0.644 0.628 0.613 0.597 0.581 0.565 0.550 0.534
75 100 150 300
Rack … … These values assume a moderate temperature increase and some initial lubrication. With bevel gearing, divide the number of teeth by the cosine of the pitch angle and use the data in the table. For example, if a 20-degree PA bevel gear has 40 teeth and a pitch angle of 58 degrees, 40 divided by the cosine of 58 degrees = 40 4 0.529919 ≈ 75, and Y = 0.434. Table 14. Safe Bending Stress Values for Plastics Gears 0.390 0.484 0.550
Safe Stress
Unfilled
Glass-Filled
lb/in 2 3,000 5,000 6,000 6,000 3,500 2,500
Plastics Type
MPa 20.68 34.47 41.37 41.37 24.13 17.24
lb/in 2
MPa 41.37 48.26 82.74 62.05 55.16
ABS Acetal Nylon
6,000 7,000 12,000 9,000 8,000
Polycarbonate
Polyester
Polyurethane
…
…
Table 15. Service Factors for Plastics Gears
Intermittent, 3 hr/day
Occasional, 1 ⁄ 2 hr/day
Type of Load
8–10 hr/day
24 hr/day
Steady
1.00 1.25
1.25
0.80 1.00 1.25
0.50 0.80 1.00 1.25
Light shock Medium shock Heavy shock
1.5
1.5
1.75 2.00
1.75
1.5
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