I guess I was trying to say 'unnecessary' load on the cross slide leadscrew nut, since with a scissor knurl you have a much cheaper screw built in the tool itself that accomplishes the exact same thing in a different plane. That screw is finer pitch, presumably more mechanical advantage to achieve knurl depth. It also runs in steel 'nuts', not a typical bronze ABL leadscrew nut. With bump style knurling tools you are kind of stuck with direct infeed. I've seen those easily bend 1/2" tool steel which would equate to a pretty aggressive cut. Bump style is also not kind to your tail stock assembly taking lateral force, but again, our machines vary in robustness. When I was shown bump style it was recommended that you don't creep in slowly. Supposedly kiss the rollers on the surface & then you gave it a faster dial twist in which helped set the deformation process. Not sure if this was related to a sort race against work hardening, or just how it works out. The instructors knurls were perfect sharp diamonds under magnification & everyone else's was shades of sh*t so who am I to argue. Actually most people had decent results on 12L14 but O1 was a different matter despite finer knurl pitch. Some just looked like cross hatching, those were the infeed dilly-dally-ers I recall.
As to how much accelerated wear occurs by heavy cutting in-feeding by itself, that's a great question. I have only seen tables that quantify power consumption to remove material X at rate Y. Parting in theory should be hard on leadscrews too, but maybe in reality we just feed at the rate its happy. Too much & usually something worse happens. I've been pretty average or probably light operating my lathe & its leadscrew/nut time this winter. Wear is a reality.
Good discussion. My own personal conclusion is I now want to try a cut knurler.
