parameter control of sketch dims

[mad_haka]

To create a wood frame family, I need to precisely notch the timbers.
To control the dimensions with parameters, length, width, depth, there is no problem.
And then flexing the dimensions works out fine.
Now when I want to make notches in the extrude profile and control the sketch
with parameters, I get a "constraints are not satisfied" message on attemping to flex
the parameters. In this case setting 'a = 27' in the parameters properties dialog box.
And the only option offered is to remove the constraints. What should I be doing?

See sketch for dimension clarification.
Load attached .rfa file to test flexing of parameters 'a' and 'b'.

[Dimitri Harvalias]

You are on the right track but you'll need to add your parameters to the family while you are still in sketch mode.
Open the family, delete your a and b parameters, select the extrusion and add your parameters to the sketch lines. Close the sketch and try flexing the family. It should work.

[mad_haka]

Hi Canuck. It works. Here's the result. I need a couple more tips, if you don't mind.

For the pin holes, how do I select the center of a circle to attach a dimension to it?
How do I declare a plane parallel to another without getting an error message when
the other one moves (due to angle changes in the parameter driven geometry).

BTW Was at UVic for a couple of years. BC rocks.