Originally Posted by
Peckish
Yes. Doing it the way you do gives you a very good possibility that you will have wavy borders, which are a pain to quilt. All those steps and measurements where things could go bad, as you say, are actually preventing things from going bad.
There's only two things that cause waves in the border (or any piecing for that matter) .- either the edge is not straight , or the stitching line is not straight with consistent seam allowances. You can take all the measurements you want, but it won't fix the real problem. The top doesn't even need to be square for good results but for the record, I square tops to be within 1/4 inch, measured diagonally in both directions. If the top piecing and assembly is as it should be, there is very little, to no trimming required.
Joining on the bias edge (such as setting triangles) can cause a little trouble if not attended to. Stay stitching helps but as mentioned you want to avoid stretch as you sew. Even when stay stitched I pin the snot out of setting triangles unless- If I have fabric to burn I place the straight grain on the outer edge, and the bias edges are joined to the top itself.
Pieced borders (ex: piano keys or seminole pieced, etc) cause a different set of problems which are easily handled by improving techniques. The biggest problems with pieced borders is pattern matching at the corners.