Need Help To Reverse Tan Tan Radius

[JET5]

I am trying to reverse engineer and generate a drawing for a gear form. I have a radius at the root of .250, and a radius at the top of .350, and a radius between then of 3.25.

 

I know the position and centerpoints of the first two smaller radii. But I do not know the centerpoint and tangency of the large radius to them. I tried to connect them using the tan-tan-radius command, but the radius it generates is a concave radius. I need a convex radius to tangent these other two circles.

 

Anyone know how to get tan-tan-radius to make a circle in the other direction or from other points on two circles? Or is there a different way I can do this?

 

Thanks,

-Jet

[RobDraw]

When you pick your snap points, place your cross hairs on the outer sides of the circles.

[eldon]

It all depends on where you select the circle for the tangency. The nearer you can touch the two circles at the hoped for tangent point, the better. You can get different results depending on the steadiness of your hand.

[JET5]

Okay that worked, just had to keep selecting different parts of the circles until it changed it's slope. Thanks so much for the help guys.

 

See attached image, the red line shows what I was getting, the green mirrored tangents show the completed gear form after several attempts. Still, it seems like there should have been a command to flip this thing. Inverse tangent or some such.

 

Anyway, again thank you very much (who would have thought to just keep trying).

 

-Jet

 

It all depends on where you select the circle for the tangency. The nearer you can touch the two circles at the hoped for tangent point, the better. You can get different results depending on the steadiness of your hand.

[BIGAL]

Our old civil software gave you the option of choosing the correct curve answer. For the circle rad circle there are actually 4 answers that match geometrically.