Do you know, that… ?

In surface modeling (but also solid), in order to obtain a smooth connection, use alignment tangent or continuous curvature.

I will now show you on the example of a bicycle frame, how the cut preparation has an impact on the result. If you are cutting a fragment in a round pipe, which will be tangentially connected to another fragment – this cutting point should be approximately through the center of the roll.

This solution is shown in the figure on the left. If you move the sketch too deep, that is, off the axis to the right – the generated tangency will form a dome (A). However, if the cut is too shallow, that is, shifted off the axis to the left, the surface will be sunken (B).

The above example has been redrawn, but it shows the correct way to prepare the surface for a smooth joint.