Ball Screw Repair


I did it myself and it worked. Whew!
The screw was full of aluminum chips and, of course, very noisy.
Midwest CNC, Dave Price, thought the screw would be ok after it was cleaned.
However, the support bearings might need to be replaced.
Yes! The support bearings, the duplex pair, needed help. Bought new! Can
you stand it! The preload on these is 750 pounds!
The serrated thrust nut has a 13/16ths 32 thread. I figured the helix angle
~ less than 1 degree. One foot pound would establish 75 lbs of thrust
theoretically.
ten ft/lbs would set up the preload except for the wedging and friction of a
'v' thread. So I will take a feel on 20 ft/lbs. I almost had to stand on
the wrench to remove it. I haven't seen any information on what torque to
set these thrust nuts.
These are off a Kmb1 Hurco "The blue machines"
The ball screw has two Ball jam nuts keyed together to establish the
preload. I couldn't remove the key so decided to unload the balls anyhow.
Each nut has two separate ball circuits. I removed the connecting tubes and
removed the balls. Took a lot of solvent to reduce the waylube and a lot of
back and forth rotation to tease out the balls.
If you do this... make sure the tubes are marked so you can replace them as
they were. !!!
I got lucky.. *Smile
The hard part was counting the balls! Accurately! into 4 groups.
Everything cleaned, I replaced the balls 70 in each circuit. Plus 15 for
the tube. 85 in all. 340 total!
A little dab of general purpose grease stuck in the tube ends keeps the
balls from falling out as you replace the tube.
I replace the balls in one circuit and tube in each nut first to establish
the preload and then finished the center two circuits. Seemed to work well.
I did this three times! First effort wasn't too good because I lost track
of how many balls were in each tube. The nut ran too rough.
Second time I was more successful. But I still didn't get the smoothness I
wanted.
Third time I called "Ball Tek" [very nice people, been around a long time.]
they had the 1/8th balls, grade 25 (roundness) .11cents each . I bought 400
for the job.
The third time was definately the Charm! Smooooooth as a baby's bottom!
I will be running the machine this week.
I don't mind tell you I was very happy and surprised.
I hope you all can feel, you too, can do this. If you want too.
Best regards,
Stan-
Reply to
Stan Dornfeld
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