Merging subtools breaking apart during subdivide

[ndsugi]

So this is an issue I have been unable to really sort out. I have taken a model that was solid, split it apart, modified it while in it’s primitive poly-state. I merge down the parts with weld applied, and then attempt to subdivide for refining and finishing details. The parts are splitting at the seams when subdivided and I don’t understand why, when weld is supposed to fix this? I tried boolean remeshing but get similar issues, tried zremeshing to project back detaisl if necessary and get the same splitting/breaking, dynamesh is the same. I even tried inserting a dummy to use boolean union but it creates many unwanted artifacts and breaks.

What am I missing here, and why is such a simple thing becoming so difficult? i haven’t done anything strange or radical to the undivided subtools, only some very basic qmesh extrusions.

first image is the low poly merged subtool, next is the same merged subtools with one subdivision level applied, causing gaps.

[tobor8man]

Try increasing the Weld distance a little and watch the vertex count to see if it comes down as the distance is increased. There’s also a open/closed circle option on Weld Points so try each algorithm out.

Crease the borders to avoid shrinking when subdividing.

Might also depend on how you split into parts. Unweld by polygroups gives a different result to Unweld by Edgeloop (ZModeler). The Zmodeler version adds some extra geo along one side. Don’t really know why and the two Weld Points algorithms produce different results (different final point counts). Perhaps a Pixo/Maxon expert can explain what the extra geo is about.

[ndsugi]

Thank you for the very helpful tips! I needed to reconsider creasing which is something I didn’t pick up in my learning journey so far. This issue has caused me a lot of headache. I still don’t really grasp the whole “WeldPoints” vs “weld” button in the merge menu, as I thought that having weld on in the merge menu means weld is enabled when merging down subtools? Or is the “WeldPoints” button with the small circle the extended menu option for that button? I can’t seem to find any information on the tiny circle in that button as well, not sure why it’s not addressed anywhere, or perhaps I missed it in my search.