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Do/Don't Ball Screws Have Wear?

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  • #16
    I have a 1952 David Brown 990 tractor. It has a ball screw arrangement between the steering column and the steering arm. I had to disassemble it last year to work on a cast steering yoke that had broken, and the ball screw and ball nut were still in good condition after 60 + years of yanking and cranking on this old tractor's steering...

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    • #17
      Originally posted by darryl View Post
      Considering that a ball screw probably is made to some specified degree of precision that's higher than what a wheel bearing would normally be, I'd say that a ball screw should have a very long life indeed.
      "Probably made" leaves allot wide open, for one keep in mind what I stated earlier, they are inferior in comparison in design from the start due to being "un-caged" if your land cruisers bearings were un-caged they would only have made it a fraction of what they have endured... ball screws may or may not be more precision depending --- but they are stone age archaic in design when compared to a common Yugo/Vega or Pinto wheel bearing...

      there are exceptions to this rule if they make them, if you introduce ball screws that have dished nylon discs inserted in-between the balls and take up all space with just a little left for freedom of movement then you eliminate the ball on ball contact, you also eliminate the "double speed" factor, you now have a pretty stable system

      this system is used in Kubota's track hoe's main swivel bearing - it's called a free cage.

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      • #18
        There are two basic ways of achieving preload on a ball screw. The most common is loading the screws with oversize balls. It is not uncommon to have the screws reballed at some point where they load a set of slightly larger balls. The other method is using double nuts loaded against each other which means they can be adjusted for preload and wear to some degree. My THK nuts are rated for 6,000 kilometers of travel at rated load.

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        • #19
          Both systems can and do outlive their owners if designed correctly.Both are subject the the same failure modes as mentioned grit and dust.I salvaged the leadscrews and nuts out of an older model Okuma CNC mill.It had multi start Trapezoidal leadscrews 50mm in diameter and the nuts were 150 mm in length.Even though the machine's hour meter had rolled over past 10,000 hours,there was maybe .0001" backlash present in the screws.These were protected with bellows and fed lube oil on a timer driven pump.
          I just need one more tool,just one!

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          • #21
            Every mechanical object with moving parts eventually wears out, unless we're talking hydrodynamic or hydrostatic bearings. It's inevitable.

            Sent from my XT1053 using Tapatalk

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            • #22
              Originally posted by Andre3127 View Post
              Every mechanical object with moving parts eventually wears out, unless we're talking hydrodynamic or hydrostatic bearings. It's inevitable.

              Sent from my XT1053 using Tapatalk
              Hey - what can I say - finally someone with an understanding of how things actually work...

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              • #23
                Originally posted by wierdscience View Post
                Even though the machine's hour meter had rolled over past 10,000 hours,there was maybe .0001" backlash present in the screws.
                at an average rate of 50mph that's right up there with Darryls 1/2 million mile toyota land cruncher claim, and yet keep in mind there's no way he was averaging 50mph so you can probably about double that 10,000 hour figure,

                also keep in mind whatever axis is being used on the machine most time's it's sitting completely idle as the hour meters continuing to run,,, not so with an odometer and wheel bearings... just saying, little perspective please and some respect for the almighty caged low quality bearing --- engineering is everything...
                Last edited by A.K. Boomer; 07-26-2017, 01:17 AM.

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                • #24
                  No backlash compensation needed...

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                  • #25
                    and that is moving around a couple ton...

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                    • #26
                      Originally posted by darryl View Post
                      Considering that a ball screw probably is made to some specified degree of precision that's higher than what a wheel bearing would normally be, I'd say that a ball screw should have a very long life indeed.
                      Given that I'm rather involved with making wheel bearings I object to that remark
                      Apart from seal failure and hard cornering wheel bearing life is virtually infinite. Almost all fatigue comes from cornering. Now these bearings are ground to extremely tight tolerances whereas a lot of ballscrews are just rolled. Even the ones that are ground are not as accurate as it's really hard to grind an accurate helix as opposed to making a circular raceway.
                      Igor

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                      • #27
                        Pro's and Cons

                        Like Ikdor states cornering is hard on conventional bearings and that is due to using a bearing in a way it's not really intended, kinda half splitting the load and trying to "shear" the balls in half with half races, creates allot of unit pressures on both the spheres and their races,,,

                        this is actually how a ball screw functions "normally"

                        But, ballscrews do have an advantage when being used this way because they can "stack" as many rows as they want to help "share" the load and conventional bearings can't,
                        But, there's only so many rows you can stack before it becomes irrelevant due to torsional deflection of the ball screw itself,
                        due to this effect the lead ballscrews from the driven side take the brunt of it all and as the screw progresses the load lessens after so many rows to the point of doing nothing at all but creating extra moving parts...

                        yet it is this stacking effect that contributes to the reason as to why they do so well, come up with a way to keep the balls from touching each other and you really would improve the longevity even more so, but from many of the examples given on some of the older machines that might be overkill...

                        there is no doubt the good quality ones do very well as is...

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                        • #28
                          Originally posted by skunkworks View Post
                          and that is moving around a couple ton...
                          Nice! What's the machine? Horizontal mill?
                          I just need one more tool,just one!

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                          • #29
                            It is an old Kearney and Trecker Milwaukeematic IIIb.

                            (using it as I type...)



                            It is my favorite machine to run. It just works. strait and true. (only complaint is coolant control...)

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                            • #30
                              Cool,am I seeing right it uses straight shank tooling and a master collet arrangement of some sort?
                              I just need one more tool,just one!

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