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Do/Don't Ball Screws Have Wear?

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  • skunkworks
    replied
    Originally posted by wierdscience View Post
    Cool,am I seeing right it uses straight shank tooling and a master collet arrangement of some sort?
    Yes - strait shank. K&T used this system for a few years. The newer generation ( like the 800) used a smaller version of this style. (mechanically barcoded too)

    This is our spare spindle guts..

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  • wombat2go
    replied
    I worked a bit ( a long time ago) on automotive driveline production machines, running 2 or 3 shifts,"365" days cycling every 15 seconds or so ( typical)
    The outer loop displacement feedback was independent of the ballscrew.
    The 4 quadrant motor control had some basic analog and uprocessor intelligence to halve its velocity iteratively at waypoints close to setpoints to
    increase displacement accuracy as the ballscrew wore out and to reduce shock and wear on it and motor.
    As the recirculating ballscrews and printed motors wore out, they were just replaced as spare parts.
    Sometimes, I recall, we got some back and cut open to see.
    They were not repairable parts.

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  • oldtiffie
    replied
    As a ball screw will move under load it will be dependent on the magnitude of the load and its directions.

    As a screw is used to "push" or "pull" a load the reaction/s of the screw (reaction/s) will be rotation, compression, pull/push.

    https://www.google.com.au/search?q=d....0.oXcSFM2i3Ys
    Last edited by oldtiffie; 07-26-2017, 08:48 PM.

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  • wierdscience
    replied
    Cool,am I seeing right it uses straight shank tooling and a master collet arrangement of some sort?

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  • skunkworks
    replied
    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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  • wierdscience
    replied
    Originally posted by skunkworks View Post
    and that is moving around a couple ton...
    Nice! What's the machine? Horizontal mill?

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  • A.K. Boomer
    replied
    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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  • ikdor
    replied
    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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  • skunkworks
    replied
    and that is moving around a couple ton...

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  • skunkworks
    replied
    No backlash compensation needed...

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  • A.K. Boomer
    replied
    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, 12:17 AM.

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  • A.K. Boomer
    replied
    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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  • Andre3127
    replied
    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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  • oldtiffie
    replied
    https://en.wikipedia.org/wiki/Ball_screw

    https://www.google.com.au/search?sit...k1.be3gR247Ri8

    https://www.google.com.au/search?q=m...w=1536&bih=719

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  • wierdscience
    replied
    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.

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