The kerf of die board which is cut by laser die cutting machine can’t be entirely 90 degrees to the die board surface. The difference is tiny, so normally you would never notice it.
For die board, the edge can sometimes be very slightly angled. During laser die cutting cuts the die, the laser beam generated from the laser die cutting machine follows a linear path. A lot of material will be burned when laser cuts, and this material vents up and out from the cut line in the direction of the exhaust.
The laser beam is completely straight, but the kerf walls of the laser die board tend to angle up slightly in a v-shape, that is because the heat is more concentrated at the top of the material and less on the other side. If less than 1 mm, the different can’t be noticed.
For laser die cutting machine adjustment, experienced operator is necessary. So that it can ensure less factors will affect the laser cutting.