On Mon, 2009-05-11 at 06:05 -0500, Jack Coats wrote: > I would like to make a rack that matches an involute gear. > > I guess we could just put in a radius of a 'very large' number, rather than > infinity. > > The square root radical would evaluate to the square root of 2, but I don't > know what > I would use as the value of alpha. > > Suggestions? > > IHS ... Jack
I believe the involute of a circle with infinite diameter, which makes the circumference a line, is a perpendicular line. The involute describes the path the pinion tooth takes in relation to the rack tooth as the pinion tooth rotates away from the rack. The involute says nothing about the tooth shape, the rack shape defines this, and can be any shape you want. My assumption is that common rack shapes are trapezoidal, symmetrical about the pitch center line because the relative angular velocity between resulting gears turns out to be constant or smooth. The common trapezoidal rack shapes have 20 degree and 14.5 degree side angles relative to a perpendicular to the pitch center plane. If you have a gear with unknown specifications, you could measure the tooth form, then use the gear's involute path to derive the rack shape. The problem here is, you need the pitch diameter of your gear to get the involute. Because of tooth base and tip clearance issues, the pitch can't be easily measured. You could roll the gear on a flat sheet of clay to make a rack, then study the shape to guess at what the ideal shape might be. There should be a a way to do this mathematically, but I haven't given this much thought. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your production scanning environment may not be a perfect world - but thanks to Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 Series Scanner you'll get full speed at 300 dpi even with all image processing features enabled. http://p.sf.net/sfu/kodak-com _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
