I am using Siemens NX & I have a problem in assembly, I tried making a separate part file by using spline curves, but in assembly after using constraints, the parts has interference (using clearance browser) between them as shown in fig 1. I tried using ''sew'' command also, but failed to achieve.

Q) My question is how can I extract a part model from that cut-out space ( by pull face) to fill that space in assembly as a separate part file (I want to make perfect contact in order to perform heat transfer calculations for conductance between both parts). I tried hard for 3 days, but failing. What is the best procedure to make part out to make it separately from assembly and later assemble the newly made part in the same assembly ?

Please find attached images in this message for fig 1 and fig 2.