Hi, Gary:
Rereading your reply, I think maybe the joining of two pieces can work. Did you have trouble with forming faces on the portion with edges only? Because, all you have to do is trace over one of the straight segments and the face will form. Then right click on the circle face and delete. Or select the circle face and delete. If it doesn't delete then the circle is not coplanar.
Again, working at such small dimensions could cause problems.
Are you familiar with Groups and Components?
