I used the Elrod Machine Quill retrofit for the Z. The Elrod quill is very nice, and expensive too! But you only get 4" of travel because of how the ballnut release works. I think the next machine I do I'll try to power the quill from the arbor that you mount the quill feed handle to. I didn't want to try to power the knee because it is so heavy and I for-see problems. I ended up putting the Mach controller back to 35KHZ and I get 96ipm rapids. I use ball mills for contouring aluminum at 90ipm and run carbide inserted facemills at 60ipm and chips fly! I used to run high end mold machines at 200-300ipm using 6mm ball mills making inserts for molds. Using the slower feeds on aluminum, I can just cut a little deeper, leaving a scallop, but they are easily polished out.