Notch perf versus Perfect Binding perf
Notch perf versus Perfect Binding perf
Ok, let's try to clear this up.
What I assume you to mean as a perfect binding perf, is simply that; a perf in the folded signature, both along the head and spine. The purpose of the perf is to let the air out of the folded sheet which allows it to lay flat. Of course there is a much lengthier discussion to be had with regard to the different perfs and their uses, but suffice it to say for this discussion it lets the sheet lay flatter thus providing a better finished product. When perfing the signature that is going to be perfect bound, there is an allowance factored in to the signature size to allow for spine trim (roughing), and head, foot and face trims. Without discussing different adhesives and machine types, in pefect binding, there is a specific amount of glue surface along the spine to which the cover material is exposed.
Notch perfing has a different explanation. The perforation made by a notch perf device is a rectangular hole and only occurs along the spine of the signature (kind of like a GBC punch). The signature is folded at these perforations. For notch binding, there is no spine trim (roughing allowance) since the notches actually create the glue surface. It not only allows the glue along the spine, but the glue penetrates in to the inner folds of the signature; more glue...stronger product. Another way to understand the notch perf is by looking at a piece of joined wood moulding. If you look at the moulding you can see what are called finger joints. The finger joints have an irregular shape which effectively increases the surface area to make a stronger glue joint. That is what the notch perf does, it increases the amount of surface area and creates better adhesion between the cover and the loose leaves of the finished book. Because there is no roughing of the spine, theoretically, you can run your binder faster while running thicker products. This is one of the reasons for a notch perf. I am simplifying the explanation, but I hope that clears up your question.
