Gear Data for Drawings Data for Spur and Helical Gear Drawings Machinery's Handbook, 31st Edition
2242
Min. Spur Gear Data
Min. Helical Gear Data
Type of Data
Add’l Optional Data
Item Number a
Data a
• •
•
1 2
Number of teeth
Diametral pitch or module Normal diametral pitch or module Transverse diametral pitch or module
•
2a 2b 3a 3b 3
•
•
Pressure angle
•
Normal pressure angle Transverse pressure angle
•
Basic Specifications
• • • •
4
Helix angle Hand of helix Tooth form Addendum Whole depth
4a
• •
5 6 7 8 9
Standard pitch diameter
• •
•
Max. calc. circular thickness on std. pitch circle Max. calc. normal circular thickness on std. pitch circle
•
9a 10 11 12 13 14 15 16 17 18 19 20 21 22 23
•
Roll angles
• • •
• • •
A.G.M.A. quality class Max. total composite error Max. tooth-to-tooth composite error Testing pressure (Ounces)
•
Manufacturing and Inspection
•
•
Master specification
•
Meas. over two .xxxx dia. pins (For setup only) Outside diameter (Preferably shown on drawing of gear)
•
•
• • • • • •
Max. root diameter Active profile diameter
Surface roughness of active profile Mating gear part number Number of teeth in mating gear
Engineering Reference
Minimum operating center distance a An item-by-item explanation of the terms used in this table is given beginning on page 2240 . Backlash In general, backlash in gears is play between mating teeth. For purposes of measurement and calculation, backlash is defined as the amount by which a tooth space exceeds the thickness of an engaging tooth. It does not include the effect of center-distance changes of the mountings and variations in bearings. When not otherwise specified, numerical values of backlash are understood to be given on the pitch circles. The general purpose of backlash is to prevent gears from jamming together and making contact on both sides of their teeth simultaneously. Lack of backlash may cause noise, overloading, overheating of the gears and bearings, and even seizing and failure. Excessive backlash is objectionable, particularly if the drive is frequently reversing, or if there is an overrunning load as in cam drives. On the other hand, specification of an unnec essarily small amount of backlash allowance will increase the cost of gears, because errors in runout, pitch, profile, and mounting must be held correspondingly smaller. Backlash does not affect involute action and usually is not detrimental to proper gear action. Determining Proper Amount of Backlash.— In specifying proper backlash and toler ances for a pair of gears, the most important factor is probably the maximum permissible amount of runout in both gear and pinion (or worm). Next are the allowable errors in pro file, pitch, tooth thickness, and helix angle. Backlash between a pair of gears will vary as successive teeth make contact because of the effect of composite tooth errors, particularly runout, and errors in the gear center distances and bearings. Other important considerations are speed and space for lubricant film. Slow-moving gears, in general, require the least backlash. Fast-moving fine-pitch gears are usually
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