Gears : was Re: Usefull Utility

>--- In CAD_CAM_EDM_DRO@y..., "Raymond Heckert" <jnr@a...> wrote:

You are correct that the shape isn't an involute but a radius. In
fact it's usually three radii.
The bottom one where the roller sits and two where it enters or
leaves the sprocket. These are the ones that differ.
As a sprocket get smaller as regards the number of teeth, these radii
alter to allow the roller to engage without interferance.
Theoretically it should be an involute but as we are talking about
rolling bearings as opposed to sliding gear teeth there is a
compromise.
This is why five cutters are needed to cover the range.
Machinery Handbook covers this as regards standards but not
explanation.

> If you're talking about roller-chain sprockets, my understanding is

that

> the tooth forms are not involute, merely a radius, since, when the

roller

> seats itself, the only relative movement is radial, with respect to

the

> center of the roller. The action isn't the same as gear teeth

which have

> to mesh, front & back sides ot the tooth, without acceleration or
> deceleration, and the tooth forms actually "sliding" across each

other.

> Therefore, you shouldn't need special cutters for different tooth
> configurations... that is, if you're talking roller chain

sprockets. Or

> did I miss a post somewhere along the line??
>
> Ray Heckert
>
> ----------
> John S. wrote:
>
> > As you say the pitch diameter doesn't change at a linear rate as

the

> > true shape is an involute. Just as the sprockets have 5 cutters

per

> > set gears have 8 per pitch and pressure angle.
>
> > John S.
>
>
> [Non-text portions of this message have been removed]