OSTexo,
You have to understand that there is only 2 ways to rebuild this cylinder from his project by do not touch botom spiral deatail, because cylinder has one radius and that spiral detail another. And spiral do not follow perfectly tappered surface of cylinder Look at the picture:



First way is with this artifacts (his):


And second with this continuity(mine):


I do not know what artifacts or continuity is worse in your way.

But to avoid all that artifacts or continuity you have to model it right from the start! - Start from Cylinder! Or made that bottom spiral some how in right way to follow surface of tappered cylinder.


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