Modeling teeth on a non-circular gear

[hoganh]

I'm about to set out on a quest to model involute teeth on an elliptical (or other non-circular) gear. Does anyone know of an easy way to model involutes, and is curve-pattern my best bet at getting teeth to follow the perimeter?

 

[SBaugh]

There is no easy way to model true involutes there is so much that has to be determined to make just one. You should go the the SW website and look under their 3D content central or model page and DL one that has already been built to get your ideas from.

Yews a curve driven pattern would be my first choice to use. If that doesn't work you might try looking into sketch driven patterns.

Regards,

Scott Baugh, CSWP
3DVision Technologies

http://www.3dvisiontech.com

http://www.scottjbaugh.com

faq731-376
When in doubt, always check the help

 

[TheTick]

I don't believe curve driven pattern would be appropriate. It probably would work fine to copy identical involutes, but I don't believe that would be the case here.

An involute is defined by the path that the end of a string would follow as it is unwrapped from a cylindrical surface. Since your gear is non-circular, each tooth would have a slightly different involute definition based on the curvature of the ellipse at any given point.

Also, if you are modeling mathematically curvature sensitive such as involutes, be aware of a flaw in the way SW generates splines. First, sketch a spline with 3 or more points. Then, right-click the spline and display curvature. You will see that the curvature is forced to zero (i.e. instantaneously straight line) at the endpoints. You can't get a true involute definition with this condition.

Fortunately, there is a workaround. Simply sketch a couple construction lines across the spline close to the endpoints. Then, use trim to lop off the ends. You can then delete the construction geometry. You will then have a spline with ends that are allowed non-zero curvature.

I may make you feel, but I can't make you think.