noise in plastic gears

I imagine most of the noise is from imprecise manufacturing tolerances,
common in molded vs. machined parts, so unless you pick some that have a
better fit, your choices are fairly limited to:

1. Carefully filing or shaping the gears to provide a better fit.
2. Adding oil or other lubricant (which can increase resistance and
therefore may lower efficiency, not to mention more mess).

Noise is inherent in any gear. Metal gears may be "quieter" because the
mass of the metal may tend to dampen the sound, but they may be no more
efficient, all other things being equal.

As gears differ as to pressure angle, face width, etc. gears of the same
pitch may not necessarily be good matches if you're concerned about
maximum efficiency and other factors. For higher end applications
pairing gears together is more involved.

-- Gordon

My experience in working with hundreds of gearboxes over the years, is that
nothing can be done to reduce your existing noise after you have set spaced
them correctly. You might try carbon paper interface to see where the high
spots are on each gear but that takes a lot of effort. You may be better off
just going to belt drives which are really quiet. Take a look inside any
cheap Chinese VCR rewinder for examples. You might also just get some
surplus rewinders and redo your device with belt drives. They are quiet. And
slip instead of break when overloaded.

Wayne

    --Try a light oil..

--
        "Steamboat Ed" Haas         :  Any Scrabble players          
        Hacking the Trailing Edge!  :  around? I cracked 500!
                          www.nmpproducts.com
                   ---Decks a-wash in a sea of words---

Thank you for the thoughtful responses.

I thought of belt drive, but it's really difficult at these dimensions.  The
tiny motor does not have ball-bearings (maybe sintered ones) and I believe
any tension on the belt will result in significant friction on the motor
shaft.

Well....I did confirm Gordon's suspicion that there were at least 3
components to the noise. One was once-per-rev (of the output gear), another
was a buzzing noise at certain speeds and lastly the teeth noise.  As
advised,  I examined the gears under a microscope and used an x-acto knife
to remove what seemed like molding defects in the pits of some teeth (more
on one side of the gear than the other).  This cured the once-per-rev noise.
I added some lithium grease to the plastic bearings on the output shaft and
this cured the buzzing noise (resonance - shaft/bearing assembly..?).  Now,
the predominant noise is the high-pitched teeth noise.  There is already
very little (subjective..) back-lash between the pinion and output gears.

Any other ideas?

Thanks again,

Kevin

    First, if you're not that familar with gear theory, take the
Boston Gear "Gearology" online course:

  http://www.bostongear.com/pdf/gearology/all_gearology-chapters.pdf

If you're getting excessive tooth noise, there's a good chance
that the tooth shapes are wrong or incompatible.  This isn't that
rare in small hobbyist-grade gears.  If the diametral pitch is different
or the teeth aren't proper involutes, the teeth won't really mesh
properly.  The gears may appear to work, but you get noise and
excessive wear.

    Gears have a quality rating, from 3 to 15.  Good injection-moulded
gears, (see wmberg.com) have ratings of 5, which is not great.
Normally, an aviation actuator would have grade 7 to 11 gears.
If you had to trim moulding defects, we're probably looking at
an AGMA rating off the bottom of the scale.

    Take a look at something like Berg part FFD105-72, which is a
72 tooth 37mm Delrin gear in AGMA quality 5.  That may be too
thick, though.  (Don't go by the picture; those are generic photos.)
You could thin it down with a belt sander.  Or see Stock Drive
Products part A 1M 2-Y48072.

                John Nagle

Kevin Gomez wrote:

Great!  Thank you.