Hi Wim, looking at the model edges shows the problem. The larger has 8 the smaller part has just 4 edges. So you need to make the objects to have equal amounts of edges. So, with the smaller part, select the long top edge and use edit/trim/add trimming points. Add a trim point perpendicular to the little edge just after the curve edge. Repeat this process at the other end of the long edge you have selected, and then repeat the whole process again on the lower long edge. Once complete you will have the result you are after.