Hurco KM3 X axis ball screw question (back lash problem)

[Billcase]

I just got a Hurco KM3 knee mill. The X axis has .010 backlash. I put an indicator on the end of the ball screw by the servo motor and the screw only moved maybe .0003 so the inner race nut is tight also the outer race is tight. I unbolted and slid the table so I could see the X axis nut. It is a double nut and very sloppy between the 2 nuts of the "double nut" ball nut. there is a split spacer in there so my first thought was to buy or make a spacer .009 to ,010 thicker. (The Rockford ball screws with the double nut have Bellview spring washers between them to eliminate back lash.) I did notice there were new thrust bearings on the servo motor end because the grease looked new, which also told me whoever had this machine had a back lash problem and installed new thrust bearings on the motor side. I took the opposite side apart and was surprised to see 2 bearings in there, and they also looked new due to very clean grease and each bearing only has one shield and they were NOT thrust bearings. I have delt with many ball screws before and they usually only have one bearing opposite the thrust bearings to stop that end from whipping around. Then it hit me: Are there suppose to be thrust bearings in that end also to push the screw back toward the motor end to take up that .010? and someone simply replaced them with regular bearings? I can not find any documentation on this.

Does anyone know if the side opposite the motor needs thrust bearings to put the squeeze on the ball nut from both directions?

I had a Excello apart once and that had some funky set up in it that pushed the X ball screw from both directions.

Any info is appreciated, Thank You.

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[Billcase]

Sorry, im not thinking right, thrust bearings on both ends would only squeeze the screw, not the nut, and the screw is solid. Does anyone know if Hurco sells thicker spacers? or is the screw simply shot? it spins nice by hand, and sounds good running it with the servo motor. Thank you for any info.

[dazp1976]

Thin Aliminium foil cut to fit between the spacers. Pack bits in until its spread the nuts tighter on the screw.
Done it with my diy mill DFU 1605 C7 screws.
Worked alright using 0.03 and 0.01mm thicknesses.
Got it down to about 0.001 (0.025mm).
Not bad for a crappy C7.

[Rich Carlstedt]

On a Hurco ( KM3) the servo end of the screw has thrust bearings , thats all you need. the opposite end is just support bearings
If there is proper preload and the bearings are the correct ones (?) there is no endplay !
If you still have end play, then it is the Ball Nut.
You confuse me by saying Rockford ball Screw ?? is that what is marked on it ?
You want a Precision ground ball screw, not a rolled thread ball screw ( cheaper , but not accurate--as the Hurco relies on servo encorder/resolver signal)
Rich