Originally Posted by
jdell42
Out of curiosity did you get your screw at Enco? They are terrible. McMaster has much better and straighter screws.
My table is 60"x60" using ENCO 3/4 x 6tpi Acme screws.....2 screws and 2 495 steppers for the X and 1 screw and 495 stepper for Y axis. All screws are about 61" long and they run pretty smooth. The steppers are direct drive to the steppers. To straighten one is not that bad. If one has a slight bend then just pull slightly in the middle the opposite direction untill it's reasonably true. It will hardly every be perfect if it's long. Acme nuts are very sloppy on the screw and I wouldn't want to use them anyway(metal to metal). I got my screws from ENCO as I stated and also purchaced a 13" piece of 1.25" Bronze bearing stock, and a 3/4 x6tpi acme tap. Generally drill sizes for taps are based on 75% threads which will have a bit of slop which will let the screw whip at higer speeds and clap as they turn. I found a bit that would give me close to 100% thread eliminating most of the slop and run a lot smoother plus making my machine more accurate and helping to cut down on backlash. Tapping close to 100% threads takes a lot more torque but it's worth the effort in this application. My unit has been running since Nov of 2006 and all is still well. If you want to see it running, go to YOUTUBE and type in "Thunderbird by Sharpie" in the search box. Hope this helps some. BTW my machine runs 60 ipm but will go a little faster.
Nick
Nick http://www.nixstuff.com
http://www.youtube.com/watch?v=jTu7wicVCmQ