# Drawing Involute curves

Does anyone know of a way to draw involute curves with inventor. So that I can make accurate gears.

Can I ask why you are drawing the involute curves? Is this for a CAD competition or for CNC’ing some custom gears? If not, I wouldn’t bother drawing the teeth. I would simply represent the gears as disks whose diameter is the pitch diameter.

I’ve never drawn an involute on CAD, so I couldn’t tell you how. However, I can tell you how to draw an involute curve on paper (perhaps that will help).

First, Take something circular (like a cylinder) and attach a string to the circle somehow. Then, wrap the string around the circle. Pretend that the tip of the string has a pencil on it. Lay the circle (wrapped with string) on a sheet of paper. Trace around the circle. Lastly, while keeping the string tight, begin unwrapping the string. The path drawn by the tip of the string is an involute curve.

If you search the net, you can probably find a mathematical formula for plotting an involute. Perhaps then you could spline it into CAD.

If you have autocad, it would be best to draw the profile in autocad, and then extrude them in inventor. You might also want to check out http://www.firstcadlibrary.com There is a spur gear i-part that i think may be accurate, but i am not certian that it is. If you need information on the involute itself then check out http://www.sdp-si.com/D190/D190cat.htm

I do realize how to draw the curve by hand with the string method. I was just wondering how you would go about doing it in inventor. I also considered the spline method the only thing is that I don’t want to do it by hand. If I had a macro then It would be no sweat. I usually represent gears by doing a cylinder that is the diameter of the pitch circle. The jest of it was that I wanted to know how to draw them my self.

The i-Gear is not a true Involute gear …