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  1. #1
    Join Date
    Mar 2003
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    35538

    Alternative to round pipe.

    While building machines using skate bearings and round pipe (gas pipe, EMT...) is cheap and easy, there are some limitations. A major one that I noticed is that you can't get the bearing really tight because the 45° loading puts too much axial load on the bearings, which greatly increases the rolling friction.

    I came up with this idea to eliminate that problem. Use a laminated wood rail for stability, and epoxy steel rails to it for the bearings to ride on. If you own a wood planar, it's easy to get two parallel surfaces for the top and bottom bearings. The bottom bearings need to be mounted with an eccentric bushing to be able to keep the assembly tight to the rails. I think the easiest route is to buy the chinese dual V eccentric bushings, and some 3/8" ID bearings for the bottom. VXB has 3/8"ID bearings 10 for $15.

    Any thoughts?
    Attached Thumbnails Attached Thumbnails Skate_Bearing2.jpg  
    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)

  2. #2
    Join Date
    May 2006
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    2420
    Nice work Gerry, I like it, nice and simple and could be used on the larger machines without any problems. I have filed a copy for later...

    Russell.

  3. #3
    Join Date
    Mar 2005
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    1673
    Nice design; thank you for sharing.

    Do you think there could be a problem with the bolts running through the top and bottom bearings bending with the pressure? I suppose it will depend on how long they needed to be? Just an observation not a criticism.

    Wish I had your CAD skills btw.

    John

  4. #4
    Join Date
    Sep 2006
    Posts
    157
    Very interesting idea. You get a lot of rigidity from the ibeam thickness and the lamination improves the stability of the wood and gives dimensional strength. Don't know much about this type of linear system but would trapezoidal give you better offsetting/sharing/dampening of lateral forces.

    Oops, maybe I'm looking at it backwards!

  5. #5
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    Quote Originally Posted by Oldmanandhistoy View Post
    Nice design; thank you for sharing.

    Do you think there could be a problem with the bolts running through the top and bottom bearings bending with the pressure? I suppose it will depend on how long they needed to be? Just an observation not a criticism.

    Wish I had your CAD skills btw.

    John
    I guess it would depend on how heavy the gantry was. As drawn, they're 8mm x 45mm bolts and about 30mm from the angle to the outside of the second bearing. How strong is a class 12.9 Cap screw? tensile strength is 177000 psi.
    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)

  6. #6
    Join Date
    Oct 2005
    Posts
    186
    Excellent idea! I know it may be overkill but based on John's comments, I would extend the top and bottom bolts longer and duplicate it on the other side. In otherwords, add a steel plate on the other side and put bearings on that side also. The top and bottom bolts would just extend through the angle on the other side. Unless you could drill the holes just right, you could make then adjustable with the size of the holes so it can be tightened to the steel plates. If you didn't want to add another bearing set on the opposite side, then just use longer bolts on the top and bottom with spacers and put a metal plate on the outside with those bolts connected. This will reinforce it with the weight of the gantry.

    Just my two cents... :wee:

    Warren
    LetterCAM CNC Software
    http://www.LetterCAM.com

  7. #7
    Join Date
    Nov 2006
    Posts
    89

    Off Topin ofr epineh

    EPINEH

    I saw this the other day and thought you would like it.
    Attached Thumbnails Attached Thumbnails binary programming.jpg  

  8. #8
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    May 2006
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    2420
    Haa! thats funny, now if only I could fit that as an avatar...

    Russell.

  9. #9
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    Mar 2005
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    Quote Originally Posted by WarrenW View Post
    Excellent idea! I know it may be overkill but based on John's comments, I would extend the top and bottom bolts longer and duplicate it on the other side. In otherwords, add a steel plate on the other side and put bearings on that side also. The top and bottom bolts would just extend through the angle on the other side. Unless you could drill the holes just right, you could make then adjustable with the size of the holes so it can be tightened to the steel plates. If you didn't want to add another bearing set on the opposite side, then just use longer bolts on the top and bottom with spacers and put a metal plate on the outside with those bolts connected. This will reinforce it with the weight of the gantry.

    Just my two cents... :wee:

    Warren

    Better than a rap around approach which would mean back to the unsupported rail; there is plenty of length to add more bearing to share the load if it were required of course.

    John

  10. #10
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    Mar 2003
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    35538
    Quote Originally Posted by Oldmanandhistoy View Post
    there is plenty of length to add more bearing to share the load if it were required of course.

    John
    The main purpose of this design was to eliminate the axial loads and have the bearings only carrying radial loads. I would think that the 4 bearings should be able to carry far more weight than I would need them to. The only drawback is that the table needs to be suspended, to allow the gantry sides to be pulled together under the table.
    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)

  11. #11
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    Mar 2005
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    1673
    Quote Originally Posted by ger21 View Post
    The main purpose of this design was to eliminate the axial loads and have the bearings only carrying radial loads. I would think that the 4 bearings should be able to carry far more weight than I would need them to. The only drawback is that the table needs to be suspended, to allow the gantry sides to be pulled together under the table.
    What about adding one more set of bearings in kind of a G set up instead of your C; the rail would be an L shape turned 90 degrees clock wise? If that makes sense, you would not need to suspend the table.

    John

  12. #12
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    35538
    Quote Originally Posted by Oldmanandhistoy View Post
    What about adding one more set of bearings is kind of a G set up instead of your C; the rail would be an L shape turned 90 degrees clock wise? If that makes sense, you would not need to suspend the table.

    John
    I've thought of trying to do that, but it gets a lot more complicated, and seems like it would be a bit weaker, having to warp around underneath.

    Now you've got me thinking what if I mount the rail near the bottom, and have the gantry side straddle the rail. One problem might be that a "trough" would be created that might fill with dust and chips. I'll think about this for a bit.
    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)

  13. #13
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    Mar 2005
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    1673
    Quote Originally Posted by ger21 View Post
    One problem might be that a "trough" would be created that might fill with dust and chips. I'll think about this for a bit.
    Adding brushes to either end to sweep the chips out may work; you could have small openings at intervals for the chips to fall through.

    John

  14. #14
    Join Date
    Oct 2005
    Posts
    186
    Since my next machine is not going to be a large one, I'm not worried about unsupported rails. So I'm going to add a support plate on the outside for the bolts to extend to. And then mount each side of the gantry on that plate and go up with it. I may add another set of bearings in the middle to help support the weight. I'll work on it in the morning.

    Warren
    LetterCAM CNC Software
    http://www.LetterCAM.com

  15. #15
    Join Date
    Sep 2006
    Posts
    157
    GER21,

    Hope the development is going well. I might wan't to sign up for one. It did cross my mind you needed the levitating table Then again when I first started looking at cnc tables I couldn't figure out what was doing what

    Quick question, any tips on where to find 3d bolts and such that could be used in rhino.

    Thanks.

    jsage

  16. #16
    Join Date
    Mar 2003
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    35538
    Quote Originally Posted by jsage View Post
    Quick question, any tips on where to find 3d bolts and such that could be used in rhino.

    Thanks.

    jsage
    I downloaded 2D drawings from McMaster-Carr, and modelled them in AutoCAD, but with no threads. They also have 3D models for download. Just navigate their website to the size you want and the download link is at the top of the page.
    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)

  17. #17
    Join Date
    Sep 2006
    Posts
    157
    Much thanks.

  18. #18
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    Mar 2003
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    Quick sketch. Not sure if I like it. Far less elegant, but it gets rid of the floating table. Seems to me the more parts that you add, the less rigidity you'll have.

    The router I'm building now has a 60" floating table, and it's pretty solid, so that doesn't really bother me too much. I think the original plan would be fine for a 36"-42" X travel, and a lot easier to fab.

    Also, While a wood planar wood give me parallel sides, I think I'd need to CNC the top and bottom edge to get them as parallel as I'd like, without any deviation anywhere. Not a big deal for me, I could do it at work.
    Attached Thumbnails Attached Thumbnails Skate_Bearing.gif  
    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)

  19. #19
    Join Date
    Mar 2005
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    1673
    Quote Originally Posted by ger21 View Post
    Quick sketch. Not sure if I like it. Far less elegant, but it gets rid of the floating table. Seems to me the more parts that you add, the less rigidity you'll have.
    I still think if you turned it 90 degrees it would be the way to go. You loose the trough and I can’t see how it would be less ridged than how you have it now. If you could add G shaped plates to either end it would be extremely ridged and you could fix brushes to them to clear chips and dust. Now I really like the design!!

    John

    EDIT: In fact it would only need an L shaped plate which could be tack welded to the angle iron.

  20. #20
    Join Date
    Mar 2003
    Posts
    35538
    You mean 90° counter clockwise? Then I'd have to mount it to the table top (or flush to it) instead of the edge. No welding, no steel, aluminum only. No room for more tools.
    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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