I am going to upgrade my leadscrews to 5/8 x 6 acme from 3/8 x 16 all thread. I need to make some sort of AB nut for the setup. I currently use the self tapped delrin plastic nut for my screw which is done on alot of the routers here on the zone. It does work well but I notice there is some tight spots that the router will sometimes lose steps if I push the feed up to 55 or 60 ipm. I have no problem running 45 (which I currently run at). I notice the screw whipping some at the higher speeds also. My idea is to make a housing for a standard acme nut to mount it to the gantry and a bracket to pull the nut towards the front of the gantry and take up the slop in the threads and also place another nut and housing at the back of the gantry pulling it towards the back of the gantry and take up the slop in the threads in the other direction. This should (as I have it figured in my twisted mind) take out the backlash from the system and at the same time stabilize the screw and eliminate whip. Please feel free to shoot holes in this theory.