Re: DIN3967


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Posted by Michael Ignat on May 23, 2003 at 18:28:45:

In Reply to: DIN3967 posted by PETE on May 22, 2003 at 11:10:20:

UPPER TOOTH THICKNESS ALLOWANCE=min backlash per gear
Some criteria:
1.function (application):
power transmission (larger backlash)
cinematic (index) gears: very small backlash
("zero" backlash=special constructions)
2.temperature variations (difference btw. gears/housing):
approx. constant: small backlash
high: large backlash
3.accuracy; (let's simplify: runout)
influence of runout on backlash measured
perpendicular to gear tooth (span direction):
= 2 x runout x sin(Normal Pressure Angle)
4.manufacture:
cut to fin. size: moderate backlash
cut teeth + heat treatment(HT): large backlash
gear grind (after HT): small backlash
5.special constructions:
double helical gears=large backlash (it is difficult to align teeth for LH and RH)
6.cost:
small backlash=accurate=expensive

TOOTH THICKNESS TOLERANCE:
Purpose: manufacture will never be perfect, so, depending on the accuracy required by the application (speed=very important), the finishing method must be correlated with the tolerance

Different companies have different practices; for general applications, most likely the following values would be OK:
-tooth thinning per gear:
0.02xModule...0.03xModule
-total theoretical backlash per gear set:
0.04xModule...0.06xModule
The actual backlash is influenced by:
runout
helix angle error
pressure angle error
spacing error
variation in the center distance (housing)
temperature variations
misalignment
deflections under load
and many other factors

In my opinion, only practice for a specific application can tell what the right backlash should be.


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