Tangential circles behave erratically when changing parameters in parametric design

[trhosking]

In this design for a timing pulley all of the dimensions are parameterised and calculated from the desired number of teeth on the pulley. Unfortunately, when changing this value the 0.15mm radius circle will frequently jump to the opposite side of the 1mm radius circle, completely destroying the geometry. Clearly there are multiple solutions to the tangency even though the black lines suggest that the sketch is fully constrained. Is there any way to constrain the small circle to alway be leftmost?

[TheCADWhisperer]

@trhosking 

Can you go ahead and create one size and Attach the file here?

Extrude and whatever other operations.

I have an idea, but need the file to test.

[trhosking]

Sure.

It seems to do the right thing when increasing the NumTeeth parameter, but when you decrease it all hell breaks loose.

[trhosking]

By the way, Just wind it back to the sketch operation and adjust the parameters in there. The extrude step is broken.