Please rank the rigidity of these linear bearing options


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    Default Please rank the rigidity of these linear bearing options

    I would like to know what the relative rigidity is of the following linear rail/bearing types and their pros and cons.
    Thanks
    CNCRP skate bearing
    V-bearings on steel angle ala Joes
    V-bearings on hardened v rails
    delrin wheels riding on 8020 ala openbuilds
    Round (SBR) rails
    profile rails (THK and HIWIN).
    Others?

    Thanks

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    Default Re: Please rank the rigidity of these linear bearing options

    1 - profile rails (THK and HIWIN).

    The rest are a bit of a guess, and the machine construction can play a role in their stiffness.

    2a - Round (SBR) rails
    2b - V-bearings on hardened v rails
    3 - CNCRP skate bearing
    4 - V-bearings on steel angle ala Joes
    5 - delrin wheels riding on 8020 ala openbuilds

    Gerry

    UCCNC 2017 Screenset
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    Mach3 2010 Screenset
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Please rank the rigidity of these linear bearing options

    Quote Originally Posted by ger21 View Post
    1 - profile rails (THK and HIWIN).

    The rest are a bit of a guess, and the machine construction can play a role in their stiffness.

    2a - Round (SBR) rails
    2b - V-bearings on hardened v rails
    3 - CNCRP skate bearing
    4 - V-bearings on steel angle ala Joes
    5 - delrin wheels riding on 8020 ala openbuilds
    Thanks for the fast response Ger. You must live on this site.

    With regards to the X axis where MOST of the force on the rail is in the down direction(weight of the gantry) are round rails more viable if I want to save some money over option 1?



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    Default Re: Please rank the rigidity of these linear bearing options

    Quote Originally Posted by tkms002 View Post
    Thanks for the fast response Ger. You must live on this site.

    With regards to the X axis where MOST of the force on the rail is in the down direction(weight of the gantry) are round rails more viable if I want to save some money over option 1?
    With round rails you have to commit to spacing the bearings further apart due to the inherent looseness of round rail bearings. That means your rails need to be longer to end up with the same working area. Now given that in many cases people using profile rails will have them too close together. So it really is a matter of what you can get away for your design and what you are making. Round rail bearings generally have more clearance compared profile bearings thus need to be spaced farther apart. Also the round rail solutions are generally not as stiff as profile rails under load.

    One way to visualize this is too consider a pyramid with its base on the ground. Stable right, it resists tipping. Now imagin an upside down pyramid. Not so stable right? Many diy designs (gantry supports) are closer to an upside down pyramid than is ideal, this puts excess load on the bearings, and even profile bearings suffer though far less than round rail bearings. For round rail I’d look at triangles tha have long edge at 45 degree angle with respect to the base. With a high mounted gantry this can result in a very wide base.

    The other problem with round bearings is that they can rotate some around the linear rail. So your gantry supports need to be able to resist this small freedom of movement.



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    Default Re: Please rank the rigidity of these linear bearing options

    We don't really have enough information to give answer other than in the most general terms since we don't know what kind of work the machine is intended for.The ranking given by ger21 is excellent and accurate.Clearly if you are intending to build a router for full size sheet materials the loads will be greater than for a laser operating over an area the size of a letter and this will affect what you may be able to make use of.



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    Default Re: Please rank the rigidity of these linear bearing options

    With regards to the X axis where MOST of the force on the rail is in the down direction
    During use, most of the forces on the gantry are in the horizontal direction, which translate into both up and down forces on the bearings.

    Gerry

    UCCNC 2017 Screenset
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    Mach3 2010 Screenset
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    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Please rank the rigidity of these linear bearing options

    Quote Originally Posted by ger21 View Post
    During use, most of the forces on the gantry are in the horizontal direction, which translate into both up and down forces on the bearings.
    Are you saying that because of a twisting force on the gantry? I can imagine of the router bit was stuck(worst case) and the Y or X motors were pushing it would cause a twisting moment on the X bearings. Is that what you are referring to?



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    Default Re: Please rank the rigidity of these linear bearing options

    Quote Originally Posted by wizard View Post
    With round rails you have to commit to spacing the bearings further apart due to the inherent looseness of round rail bearings. That means your rails need to be longer to end up with the same working area. Now given that in many cases people using profile rails will have them too close together. So it really is a matter of what you can get away for your design and what you are making. Round rail bearings generally have more clearance compared profile bearings thus need to be spaced farther apart. Also the round rail solutions are generally not as stiff as profile rails under load.

    One way to visualize this is too consider a pyramid with its base on the ground. Stable right, it resists tipping. Now imagin an upside down pyramid. Not so stable right? Many diy designs (gantry supports) are closer to an upside down pyramid than is ideal, this puts excess load on the bearings, and even profile bearings suffer though far less than round rail bearings. For round rail I’d look at triangles tha have long edge at 45 degree angle with respect to the base. With a high mounted gantry this can result in a very wide base.

    The other problem with round bearings is that they can rotate some around the linear rail. So your gantry supports need to be able to resist this small freedom of movement.
    My gantry plan is to have a short riser (maybe 3 inches or less) on the gantry and have a work surface that is below the X axis bearings maybe 3-6 inches.
    Like this
    Please rank the rigidity of these linear bearing options-gantry-support-jpg



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    Default Re: Please rank the rigidity of these linear bearing options

    Are you saying that because of a twisting force on the gantry? I can imagine of the router bit was stuck(worst case) and the Y or X motors were pushing it would cause a twisting moment on the X bearings. Is that what you are referring to?
    Just the forces from accelerating the gantry and cutting will impart a lifting force on one of the bearings.

    With regards to the X axis where MOST of the force on the rail is in the down direction(weight of the gantry) are round rails more viable if I want to save some money over option 1?
    Personally, I don't think round rails should be used at all (for any machines), so I can't say they'd be more viable.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
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    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Please rank the rigidity of these linear bearing options

    Quote Originally Posted by ger21 View Post
    Just the forces from accelerating the gantry and cutting will impart a lifting force on one of the bearings.

    Got it
    Thanks

    Personally, I don't think round rails should be used at all (for any machines), so I can't say they'd be more viable.
    Lots of people are using them but I appreciate your opinion.



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    Default Re: Please rank the rigidity of these linear bearing options

    It always comes down to whether you want a good machine, or a cheap machine.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Please rank the rigidity of these linear bearing options

    Quote Originally Posted by ger21 View Post
    It always comes down to whether you want a good machine, or a cheap machine.
    Ya I got you there.
    Any comments on the picture I posted above?
    I think having a lowered work surface rather and a raised gantry should be stronger, right?



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Please rank the rigidity of these linear bearing options

Please rank the rigidity of these linear bearing options