We all know that notches are important. I think of notches, grain line and seam allowances as an international language embedded into the pattern. Without anything written in text the pattern can still be 'read' by these symbols. I have a set of conventions that seem to have served me well over the years but I would like to know how others use notches. Can there be too many notches? What are your most useful tips to help the machinist. How do you use them? These are my guidelines.
There are two types of notches - Seam value and Balance marks.
Seam value notches are only put in one direction at a corner, on the seam that will be sewn first. Two nips, one in each direction of the corner will weaken the fabric. The exception is at the hem when the hem value is 4cm or more.
Balance marks are there to show how the garment goes together and must be completely unambiguous. So only put a notch in the center of a seam line if it really is the center, such as CB or CF. In this way a panel cannot be put in up-side-down.
Convention puts single notches toward the front and double at the back. Think of the sleevehead. So what happens when there are lots of panels? I use singles in varying spacing toward the front and a triple if I really need to at the back.
Double notches must be at least 12mm (1/2") apart, again so that the fabric is not weakened. But spacing them at say 2cm or 3cm gives a variation to the double notch.
Long seams need a few singles along the way to help the machinist avoid stretching and easing.