With respect to your shear! Don’t know the brand but it sounds like
it is a large one or at least a precise one.
If you are a machinist or of a sort of skills, take the blades, Both
of them, to a good machine shop and have then reshape (Sharpen in our
words) the cutting edge first and then mill the flat of the blade.
Make sure about the tension-pressure of the blades, if they or spring
loaded. If your machinist doesn’t know what you are talking about,
take it to a real machine shop. You will pay but you will have the
most beautiful cuts and very little clean-up, all my boxes have 90
degree angles. Call if you need anything, 210.260.0662, Stephen
Wyrick, CMBJ, CMP, GIA-All (I like education)