I'm no expert, in fact, I'm not even skilled in this myself. But
just based on what you describe, it sounds like a problem with
the smoothness of the blade-falling-action, if you know what I
mean. Is this a manual one, or automatic? I've only even tried
cutting a few times myself, and found it very frustrating, and the
problem I encountered most was the one you describe. I always
ascribed it to the speed/motion of the blade across the sample.
Perhaps this is just too simplistic, especially since you have
years of experience.
*** Disclaimer: These are the opinions of the poster not Amgen Inc.***