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'[OT:] Non circular gears'
2004\06\14@215903 by

We (me anyway) are accustomed to thinking of gears as being circular.
However, pairs of unlikely looking gears matched to each other can remain in
mesh throughout a rotation cycle, just as circular gears do, but impart a
wide range of useful relationships between the input and output parts. eg
linear forward motion to a slider with quick return, stop and dwell motion
etc

This company provides a wide range of non-circular gears.
Interesting examples provided.

http://www.cunningham-ind.com/

____________________
ref from Ken Mardle.

SAMPLE

Elliptical Gears:        An ellipse is defined by a set of points in a
plane, such that the sum of the distances from two fixed points - the foci -
to any point in the set is a constant. This enables elliptical gears cut
about their foci to run at a constant center distance. The velocity ratio
resulting from elliptical gears varies between 1/K and K during one cycle of
speed change, where K is the maximum gear ratio. Multilobe gears can be
derived from unilobe gears. In appropriate situations, elliptical gears may
be cascaded to obtain varying speed-change characteristics, giving an
effective ratio of from 1 to K^2 . Bilobe gears (oval gears) have been used
in flowmeters and pumps. Using precision elliptical bilobe gears, flowmeters
can have good linearity over a wide range of flow rates and viscosities

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> This company provides a wide range of non-circular gears

Are they the engineering equivalent of abstract artists who
can't draw faces ?

"We're just hopeless at doing proper circles" ;-)

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What not to do with cogs

http://www.lhup.edu/~dsimanek/whoops.htm

and other engineering oversights

--

Some employees at a company that I was once employed at built a clock using
elliptical gears as joke. The owner thought that everyone should be at work
ALL the time. Joke was that the hands would slow down during the work day. I
am not sure how it really worked out though. It looked cool at least.

{Original Message removed}
At 10:27 AM 6/15/2004 -0400, Fred Hillhouse wrote:

>Some employees at a company that I was once employed at built a clock using elliptical gears as joke. The owner thought that everyone should be at work ALL the time. Joke was that the hands would slow down during the work day. I am not sure how it really worked out though. It looked cool at least.

Didn't analog computers, like the norden bombsight, use this sort of thing?

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Not non-circular gears, but related.

Spur gears - design notes and information.
Looks excellennt.
Ref from Ken Mardle

http://www.mech.uwa.edu.au/DANotes/gears/home.html#top

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A friend of mine used to work for a firm making
labelling machines.  They had to build one to put a
label on a bottle with a wide oval shape (it was for
some sort of cosmetic, like hand-cream) where the major
axis was about 4x the minor.

He discovered (although I'm sure other people knew
before) that a pair of same-sized (circular) gears
mounted eccentrically and properly meshed have an
overall 1:1 ratio per revolution, but the movement of
the output is non-linear in relation to the input within
each revolution.  It was just what he needed to rotate
the bottle in time with the feeding of the label onto it
(that is it rotated the bottle to give a linear feed of
the circumference past a given point despite it being
non-circular).

Cheers,

Howard Winter
St.Albans, England

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{Quote hidden}

The same effect is used on push bikes which have ellipitcal sprockets to
help keep the rear wheel torque more constant throughout each stroke.  Not
sure if these are still in favour, but they were a big thing some years ago.

Regards

Mike

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