hi david, At first i was unaware that you guys were air cutting so please ignore my comments on tool sharpness.
A centralizing screw is just a tighter clearance between the nut and screw esentially, A general acme screw and nut tends to have more "slop" in it and can therefore bind much easier when shock loaded or side loaded.
Side load is just that, a force acting on the side of the screw and nut assembly (perpindicular to the way it is moving).
If you try to move a acme screw to fast right from rest it is possable that the initial shock loading can bind your assembly.
Resonance on the other hand is a fancy word for electrical vibration. You never want your amps and voltage to be at a point in the phase where they resonate, it will cause heat and ruin your drives or motors. This is why volt ref(vref) and gain adjustments exsist in drives, to tune out the amp and voltage phase I believe (correct me if I am wrong) that you do not want your amp and voltage to be converging at the sametime, normally one is ahead of the other by 90 degrees. adjusting the vref shifts the phase so they dont converage at the sametime.
What fixitt is saying is not only are you experienceing this resonace electrically, your acme screw itself, when turning is adding more mechanical vibration which amplifies the condition, causing miss steps and stalling.
Perhaps an upgrade to rolled ball screws would also help?