Hi Annet,
Thanks a lot for the file, very much appreciated.
This problem is caused by too many points pulling on the mesh, especially when they are triangles. The best case is when only four-sided polygons (quads) are used. But reducing the amount to eight can support a smooth result already.
In the screen capture below, I show you a reduction technique that works most of the time. (Somewhere in the tutorials series “Industrial Holes,” I introduced them here a while ago.
Anyway, here is a short run-down of the technique based on your model. Please note that even with the preparation done, the success of this method is based on the last step: moving the Loop-Selection carefully in place.
Screen-capture (can be downloaded):
https://www.amazon.com/clouddrive/share/KryezHVQmYSYYC4IlXZCO2aMvWlI9U3jnZPKJC8rudP
A preview image:
https://www.amazon.com/clouddrive/share/Gkg2PsJ3CgwgXAXD6xS3Q4VeeR091LifiQsYMuZEvnh
The remaining eight polygons could be reduced to four with the melt (one by one) to improve the result even more.
Preview of that extra step:
https://www.amazon.com/clouddrive/share/sE5S5riSBEhpYjlUotdHR9yZSivFtvl7V76LOP5x4jo
All the best