Joe,
I am going to have to switch my lead screws also due to excessive whip, so I am watching what you are doing closely and have a few questions. You stated only 3 thread clamps were needed. Are you not using them on both ends of the rod? And if not, what are you using on the motor side? What source did you use for your spring and did you drill the nut out to use it as a washer in the picture of your preload setup that you posted? Hope this is not too many questions at one time. Thanks for all your help.