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Intermitent gear question

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didear

didear

Mechanical
Aug 29, 2003
3
I am developing a toy that has a special set of spur gears that create intermitent motion. There is a large driving gear (64 teeth) and a small pinion gear (8 teeth) that are spaced to mesh perfectly. The large gear has 48 teeth removed so that it only engages the pinion 1/4 of the time. It rotates at 2RPM and as it comes around it engages with the pinion, causes it to rotate twice and then continues on free of the pinion until it comes around again. My question: Do you need to modify the first few teeth on the big gear that engage with the pinion? I had heard that making the first tooth 1/2 height and then removing the second tooth would insure good engagement. Is that true?

Thanks,

David
 
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It is a good idea because reducing the addendum (exterior part of the gear's tooth) would reduce or eliminate then possibility of the full height teeth from clashing one into the other when they try to mesh at each revolution and it should not induce any error in your 2 full revolutions of the small gear per rev of the big gear.

SACEM1
 
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Is there a specific design for the leading few teeth- angle/height? Are there tried and true specs for this application? Thanks.

-David
 
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didear:

search in all the books I've got for gears, and they are quite a few, and no mention as to specs for interrupted gear design, so maybe someone else can give us help there. if there exists some specifications.

I think that the only reason to modify the first tooth of the 64t gear, in the 16 teeth left, would be if the 8t gear is able to rotate freely or if it has inertial movement when disengaged from the propelling gear and rotates out of sincronization.

I drafted both gears and assumed that this happened and from those drawings in secuential order with diferent positions of the standing (8t gear) you find that there is only a small angle sector where the teeth of both gears might clash one with the other, and shaving the first gear down to the primitive line, one addendum down from the outside solves this, maybe you can get hold of a CAD program that allows you to simulate this but I don't have one installed yet.

SACEM1
 
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Didear

During the time that the 8 tooth pinion is free to spin, if it spins 2 revolutions, then engages again, wouldn't this be the same motion as you would have otherwise? Are you trying to create a situation where the pinion rotates more than two times during the rotation space in the large gear?

 
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If the outer is going to drive the
small pinion, I would relieve the first
tooth. The 8 tooth pinion will
be heavily undercut and may not have
arc of approach action. What kind of
pressure angle are you using? You are
speaking of external gears without profile
shifts? I am not certain why someone
would want to remove the second tooth.
 
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