Below are a few suggestions to try out: 1. Check geometry for any corruptions using Right Click –> Check Geometry. Sometimes model may look OK, but may have hidden corruptions not visible to naked eye. This will help to know if there is any corruption in one of the bodies participating in Combine, which can be fixed first before doing combine. It is very much possible if starting model is corrupt, resulting model may also have some corruptions (Junk In –> Junk Out, and these corruptions may be at much elevated level based on my experience). 2. Select a body, detach all faces, stitch and then you discover some errors. Some model seem like if they were pre-constrained and as soon you split a face, repair it, combine…it locally exploded creating a corrupted face or geometry. 3. It is also possible that the bodies on their own are clean, but when combined they create corrupt geometry, specifically non manifold topology. SpaceClaim won’t let you have 2 holes in 1 solid be tangent to each other because the thickness between them is 1/infinity or approaching zero and that breaks the fundamental rules of solid geometry wrt #faces, edges and vertices that define a solid 4. If the solids are clean but still have a combine issue, we often cut the bodies up with planes, first just in half to see if one half combines correctly after being cut. If one side merges and the other doesn’t, continue cutting up the non merging side till you find the issue and fix it.