Acceptable deflection for a live center
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    Default Acceptable deflection for a live center

    Just trying to get a frame of reference here.

    I broke my own rule and tried a $30 flea-bay live center on a whim. Lo- and behold, it has easily a thou and a half of deflection just from wiggling it with my fingers.

    Obviously this is unacceptable. It's nothing more than a paper weight for all the use I'll ever get out of it with that kind of deflection. I'll be replacing it with a proper tool shortly.

    My question is what sort of deflection is considered acceptable for a real live center? Do the nicer ones use tapered roller or angular contact ball bearings under preload to achieve their precision? What brands have people had good luck with? Are the spring-loaded ones worth the extra money if I plan on hogging material between centers? Constantly babysitting my dead center pressure with changes in material temperature gets old quick.

    Thanks.

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    You may not be getting a good read on the real deflection and runout unless you apply a thrust load. Even my good USA centers show a little slop unless loaded. Oddly enough, my relatively inexpensive Skoda center has very low runout and repeats super-well. It was good bang for the buck.

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    Yes check the runout under compression. Some unloaded slop is normal for most centers.

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    Quote Originally Posted by Just a Sparky View Post
    Just trying to get a frame of reference here.

    I broke my own rule and tried a $30 flea-bay live center on a whim. Lo- and behold, it has easily a thou and a half of deflection just from wiggling it with my fingers.

    Obviously this is unacceptable. It's nothing more than a paper weight for all the use I'll ever get out of it with that kind of deflection. I'll be replacing it with a proper tool shortly.

    My question is what sort of deflection is considered acceptable for a real live center? Do the nicer ones use tapered roller or angular contact ball bearings under preload to achieve their precision? What brands have people had good luck with? Are the spring-loaded ones worth the extra money if I plan on hogging material between centers? Constantly babysitting my dead center pressure with changes in material temperature gets old quick.

    Thanks.
    Riten publish.

    Heavy Duty Live Centers | Riten.com

    And there is nothing "cheap" about Skoda. Just good value for money.

    Sort of a "habit", that part of Old Europe, such things are.

    You are using "Cimcool" AKA "pink slime" on your DC?

    If not, why not? It just ain't that expensive. Centers can be.

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    a cheap mt2 live center may be able to deflect under load as much as .050" before reaching its strength limits. i know this because i've used them to stabilize a shaft with that much runout and its pretty incredible to watch it bend that much... that's just due to how far it sticks out of the mt2 socket and how far the tip of the live center is from the mt2 shank and how far the tip is out of its bearings.

    a better quality mt3 live center should be something like 10 times stiffer just due to the increased shank diameter, stiffness follows the 4th power of the radius or diameter of a round shaft.

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    Agree the live center must be under load to run at its best.
    The live center spindle has to be made between centers to run true. Made any other way and it can run dead true. One of my tasks was regrinding solid and live centers to near zero detectable error with existing bearings, or the bearings replace with new. Some/many bargain imports lives could not be made to run true even with new best bearings installed. With the spindle shaft made in a chucker with 25 millionths to 2 tenths error, the shaft will have a wobble and even grinding the spindle point in place running in the best new bearings will not run true.
    A live advertised .0002 is likely to produce .0004 error on a part.

    Good to run apart with the part and the live center point having a line-up mark, after done give the part a 180* rotation and check with a tenths indicator for TIR.
    Decent lives are advertised .0001 or 50 millionths and often come with near zero.
    Agree most work Ok with some run out, but to put precision bearings on a bearinged shaft with the bearings set on a .0002 to .0004 wobble is not good. Dead centers are best for a bearinged shaft or any high precision need.


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