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Originally Posted by sanddrag
Could you please explain to me (or show a picture) of what the involute surface and hobb is? Thanks.
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Let's start with the easy one first. A hobb looks a lot like a rack from a rack and pinion. I've only seen them in pictures but I'll try and explain them. The teeth on the hobb are trapezoids with the angle on the trapezoid being the pressure angle of the gear. When making a gear, a blank is placed on a rotating shaft and moved up and down in relation to the hobb. The hobb scrapes out one gap, then they rotate the gear one tooth and do it again. They keep it up until the gear is done. Or something like that.
The involute is a particular kind of curve. The easy way to picture it is to place a string on a round object like a can. Put a pencil in the string and unwrap the string while keeping the string tight, The shape you get is an involute. There is mathematical equation for it, but it is ugly. This year I generated a 30 degree pressure angle gear. It was a royal pain and took me several tries to get it right. Even then it was an approximation. I generated several points and then used a spline to connect them. The method I used to generate the points would take me at least a couple of pages to explain. If you do a google seach on Involute you will find tons of info including instructions on how to do a gear in CAD.
If there seems to be a heavy demand I'll do a paper on the creation of involute gears, but not until after Atlanta.
Chris