Re: Gear noise problem


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Posted by B Simpson on July 18, 1999 at 09:09:02:

In Reply to: Gear noise problem posted by Mark Lehnert on July 18, 1999 at 09:00:30:

Mark,
I am no authority on gear noise, but I would make the following comments:
With such a small pitch, mounting alignment and tolerances are critical.
Small changes in gear mounting positions can easily create problems. Usually
to accommodate manufacturing and assembly tolerances in inexpensive gear
assemblies, larger backlash allowances are designed into meshing gear sets.
Larger backlash allowance reduces the possibility of binding and
tooth-to-tooth interference (Increasing backlash can create other problems,
so this may not be appropriate in your case)

Gear whine (constant sound, tone changes with speed) often is due to
imperfections in tooth surfaces and high speed. High viscosity lubs can
sometimes help, but using helical instead of spur gears and correction of
tooth surfaces (usually by grinding, shaving, or lapping) are the best ways
to reduce whine.
If wear and strength can be traded for noise reduction then nylon, delrin
or other synthetic material could be considered for one or more gears to
reduce metal-to-metal tooth contacts. Most of the noise occurs at the input
gear set. The input gear sees highest tooth velocity and also is the set
subject to lowest torque, which may permit a plastic gear. High speed input
sets also see high wear, so pitch size may need to be enlarged to retain
design life and resistance to shock failure.

Clicking noise suggests gear tooth tip or root interference. Whine is
annoying, but clicking or popping sounds are usually indicative of premature
gear tooth failure. Louder clicking noise under load may also indicate that
gear mounting positions are distorting under load. Louder clicking under
load further confirms that there is tip (or root) interference in one or
more of the gear meshes.
To eliminate tooth interference:
(1) Increase pressure angle of problem gear set(s). Problem sets are meshing
pairs with large tooth/tooth gear ratio.
(2)Increase pinion diameter which reduces pinion undercut and increases
effective pressure angle. This is often done on planet gears which usually
have a small number of teeth.
These design options are commonly recommended to eliminate tip and root
interference since tooth beam strength is improved, and backlash is not
affected.

If you can do a subjective hands-on test, I would hold the output shaft to
simulate load, then rotate the input shaft by hand, slowly. Rotating the
input shaft should feel completely and absolutely smooth - no roughness or
sticking at any position. If you sense sticking or clicking, then tip or
root interference is likely built in to the gear tooth geometry. Gear design
should be modified to incorporate larger pressure angles and pinion
enlargement. There are books (Machinist Handbook for one) that give
recommended amounts of pinion enlargement based on gear ratios, etc.

There is another forum at http://www.qtcgears.com that may put you in
contact with others more experienced with your type of design.

HTH


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