Hi glmr,

As a first simple and straightforward test you could use the "blend" command.

Select the first two edges on the same side of both sufaces and run the "blend" command.

Then, select the two surface edges on the opposite sides.

Ciao.

Marco (mkdm).

Thank you!

Hi glmr, also if those ending curves are coplanar you can build a planar cap surface by selecting them and running Construct > Planar.

It's difficult to tell things like if they are coplanar just by looking at a screenshot so that's why it is helpful to post the 3DM model file with your objects in it instead of only a screenshot.

- Michael

thank you! already tried and it works