ME 360 – H13
Name _________________________
1) Determine minimum face width for a spur gear pair based on static yield tooth bending
failure. Assume tip loading. The input pinion is driven by a 2 HP electric motor at 1800 rpm
with moderate shock loads on the output. Use “gear_AGMA.xls” from the class web page to
check for interference. Attach hardcopy of the spreadsheet with your values.
NFS = 2
pd = 18
F _______________
 = 20°
NP = 19
NG = 57
interference ?
YES
QV = 7
1045 cold-rolled steel
NO
2) Repeat problem 1) for fatigue with 99% reliability over 107 mesh contacts using hardness HB
from Table A-9 and Grade 2 unmodified fatigue strength from Figure 12-25.
F _______________
3) The planetary speed reducer shown below is used in the Black and Decker cordless
screwdriver dissected in class. An exploded view of a similar Craftsman cordless screwdriver is
also provided below. Determine the reduction ratio for stage A and the total reduction ratio for
the complete reducer.
stage A
10A
_______________
9 A
total
10A
_______________
9 B
Stationary internal ring gear 5
inside housing 5
N5 = 48
Not to scale
Sun pinion 10
10A attached to motor shaft input
10B attached to planet carrier arm
N10 = 6
Planet carrier arm 9
9A carries planets 7A and drives sun 10B
9B (hidden) carries planets 7B and drives output shaft
Planet gears 7
7A carried by 9A, engages 10A and 5
7B carried by 9B, engages 10B and 5
N7 = 19
ME 360 – H13
Name _________________________