Hi Mstrkey
Your eyes are good - the blade is bad. You see a normal physical reaction of a cutter.
Please imagine a wedge going through something thick. Let’s say you force a big chisel through a piece of wood with a thickness of half an inch (1.25 cm). You put the wood on the floor and you force the chisel vertical into the wood. The chisel will enter the wood. And after entering a bit, you get across to the wedge (now horizontal) extreme high forces. These will either forth the wood to collapse at the angled side of the chisel (never at the straight side) or the wood will be torn into two parts. If you cut in your cutting machine thick board and you check the edges using a lens you will see this physical reaction as well.
When cutting paper you have different factors helping or damaging the cut.
Angle of blade
Assuming you would have a blade with an angle of zero degree you would never see a difference between the cutting edge behind and in front of the knife. Assuming you would have a blade with an angle of ninety degree. Booooooooooom - no further explanation necessary …… At the end you have to trust in the experience of the cutter supplier, the feedback of other customers to your knife grinder (his experience) or people like me how show up as clever. The correct angle would be today 23 or 24 degree.
Sharpness of blade
As sharper the blade as less trouble you have (up to a certain point). Doll means, the blades has already a radius at the front. If you picture a radius, you have any angle from 90 degree down to the grinded angle (maybe 23 degree).
Design of the cutter
Modern cutters have a downward and sidewise moving knife. This gives you two functions in one motion. The vertical way through the material is the cutting like using the chisel. The sidewise movement gives you something like a saw. If the knife is fresh and the blade looks nice polished it is just the opposite. The blade is ruff from the honing stone (last function during the grinding process). We cannot see this, but the knife works like an ultra-fine micro saw. The knife cuts nice and you may hear a little sound. If the knife is doll, the blade has a radius and is polished by hundreds of cuts. The blade will be no more a saw. The blade is no more cutting, the blade is squeezing. The cut is ruff and the nice sound is gone. Maybe you even hear a bang during cutting the last sheets.
Type of blade
As harder the blade itself is, as better it cuts during the diagonal movement of the knife.
If you use the standard knife (Sweden steel) or a knife with chromium, the blade is relatively soft. This means the maybe cuts for a short time okay, but quick you deflection and a rough cut.
The next better knife is high speed steel. This knifes can be used for all jobs and they do a good work.
The sharpest blade is tungsten, because the saw effect is better working. And this knife stays much longer, because the particles are harder. But tungsten blades are fragile like glass.
Internal pulling strength of the paper
As better the binding of the individual fibers is, as less trouble you have with the cutting edge in front of the knife. And the type of fibers as well as the direction (!) of fibers chances a lot. The internal pulling strength is roughly 1 to 3 in relation to the direction of the fibers.
Thickness of material
The angle (wedge) of the knife gives you more problems if the material in the cutter is thicker (sheet thickness not pile height). The specialists say that a knife can cut a third of the sheet like we understand or watch a cut. The middle part is a zone between cutting and braking. And the last third is just braking. But because paper is very thin, you don’t see anything from the braking zone.
Age of paper
Yes, yes, as older the paper as higher is the loss of the internal strength. This may start with an age of five to ten years (depending on the type of paper).
I hope answers your question (I can't for the life of me figure out why this happens.)
Have fun
Coloured paper
