loci for tooth contact

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Delce
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loci for tooth contact

Post by Delce »

Im fascinated by gears, so much to learn

Does anyone know if theres an app or some way of plotting the loci of tooth contact for two round spur gear meshing
I know its supposed to be a straight along the line of action - but is that really always the case
I can see the great animations shown here
https://www.tec-science.com/mechanical- ... ile-shift/
how did they do that?

but I am still skeptical I think :problem:

cheers
hope its not a dumb question
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ArtF
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Re: loci for tooth contact

Post by ArtF »

Hi:

No dumb questions here..

Looks reasonable to me. The line of action is a function of the pressure angle and
the points on the line move with the rotational distance of the pitchline.
Ive never had cause to plot it, haven't seen anything that does.

Art
Delce
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Re: loci for tooth contact

Post by Delce »

The situation can arise if you are using a tooth form other than involute, eg cycloid
I want to establish what kind of rubbing across faces of the teeth occurs ie tooth friction as opposed to rolling contact where friction is assumed zero
different pressure angles produce different results eg 14.5 vs 20
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ArtF
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Re: loci for tooth contact

Post by ArtF »

Ahh, I see what you mean. You want to see not so much the line of action, but the slipping while rolling
that occurs. I cant think of any way to easily compute that from the equations of mesh or anything.
Is this a question of trying to figure out the friction during motion?
Delce
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Re: loci for tooth contact

Post by Delce »

Indeed, friction
AGMA the protectionist mafia has concentrated on designs of gears that were (years ago) economical and profitable to produce given the limitations of machinery of that day
With the advent of CNC all manner of possibilities become open to investigation
I want to find a way to simulate these possible profiles

things to be examined eg
Variation in torque/ angular speed

I am amazed at how difficult it is to actually measure a gear - causes sharp intake of breath and a lot of huff puff :yawn:

I was wondering if your Augie kinematic thingy might be pressed into showing a cylinder moving along a curved surface or is it too easily upset by micro collisions, so that the transition between slipping and rolling will be lost?
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ArtF
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Re: loci for tooth contact

Post by ArtF »

Hmm. It would be a very hard thing to simulate, perhaps not as bad to quantify numerically.
Im not so sure much variation is there thinking of it generally, in theory only
one contact point is making on the mesh and it is sliding on a circular arc on the tooth
of its mate, the friction function is likely a generalized function of the pressure angles
effect on that slope. Ill have to give it some thought..

Any pertinent reading material out there on the theory?>

Art
Delce
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Re: loci for tooth contact

Post by Delce »

Im afraid that google is such a mass of disinformation its doing my head in. Im not attached to a Uni so dont have access to research papers. I daresay that this has been looked at
IMHO the japs are way ahead on gears
I just want to look at whats really going on at surface level not the superficial calcs that industry pushes out

just imagine you are handed one small gear with lots of teeth, what can you measure - OD and No of teeth, all the rest in conjecture (assuming you dont have high power inspection microscopes to hand)

you can feel the effect of poor gear design when you take a spur gear pair of say 5:1 or even 10:1 and try spinning the wheel on the pinion and notice the effort needed assuming negligible shaft friction
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Re: loci for tooth contact

Post by ArtF »

Delce:

There's a lot to unpack there. Its true that many gears wont spin well in
mesh but there are also many reasons for it. No design is perfect, but the
involute tooth is as close as I think one can get. The friction, in theory should
be the lowest as the flank only touches on one theoretical infinitely small spot
at the pitchline. As the tooth moves, that small point slides by a distance
equal I suspect to the chordal difference in gear arcs.
Some will be tight if they fit too perfect, some will be loose, for oil film
layers and such. Some profiles, like the cycloidic on clocks were
simply designed to eliminate trouble with dirt and dust fouling them
and run very loose with little contract.
I use the publications of Feydor Litvin, a brilliant person on the theory
and math of gears and meshing. All Gearotics gears were based on his formulas
and then modified at times to match industry specs. His papers aren't hard
to find, you may want to give them a read as to surface effects.

Also, you may want to search instead for the tooth characteristics of bevel gears,
there seem to be more papers on that mesh space analysis than regular gears
when I was researching such things.

My own view is that the involute is unmatched in its abilities in almost every
circumstance, though many modifications exist to things such as rear flank
on a uni-directional system..

Yell if theres anything I can point you towards.
]A rt
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