I may have under sized my gantry beam. - Page 4


Page 4 of 7 FirstFirst 1234567 LastLast
Results 37 to 48 of 73

Thread: I may have under sized my gantry beam.

  1. #37
    Registered
    Join Date
    Mar 2011
    Location
    USA
    Posts
    129
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    OK so what do you think of my post #34?
    Thanks



  2. #38
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    United States
    Posts
    32944
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    I'd go with the 1/4", and yes, add the internal bracing, as that will help to resist twisting.

    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)


  3. #39
    Registered
    Join Date
    Mar 2011
    Location
    USA
    Posts
    129
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by ger21 View Post
    I'd go with the 1/4", and yes, add the internal bracing, as that will help to resist twisting.
    the 4x6 or the 5x5?
    Thanks



  4. #40
    Registered
    Join Date
    Jan 2018
    Posts
    26
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    I would go for the 4x6 and mount the 6” dimension vertically.






    Sent from my iPhone using Tapatalk



  5. #41
    Registered
    Join Date
    Mar 2011
    Location
    USA
    Posts
    129
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    OK how about this design.
    This looking from the end of the gantry
    I may have under sized my gantry beam.-gantry-jpg



  6. #42
    Registered
    Join Date
    Mar 2011
    Location
    USA
    Posts
    129
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    bigger pic
    I may have under sized my gantry beam.-gantry-jpg



  7. #43
    Gold Member
    Join Date
    May 2005
    Location
    USA
    Posts
    3690
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by tkms002 View Post
    bigger pic
    I may have under sized my gantry beam.-gantry-jpg
    Not bad!

    As for the steel beam you might try seeing if you have a local steel supplier to industry. Around here that might be Klien, Ryerson and a couple of others that escape my mind. The idea is to get the best price possible for the beam.

    The primary problem with beam thickness selection is suitable thread holding capability. That is after you drill and tap the beam you want confidence that the threads will not strip out. Depending upon the rails being used you may be using 5 or 6 millimeter screws to fasten the rails to the beam. In an ideal world you would want at least 1.5 times the screw diameter in the beams thickness. Unfortunately that leads to a heavier beam than might actually be required from the deflection standpoint.

    Note that all welding you do will add to beam distortion. How much depends on many factors but good fit up makes a big difference. You don't want to weld up your X rods in loose fitting holes for example. I tend to prefer plates welded into the beams with weld beads on all four walls, especially on thinner walled beams. Again though, you do run the possibility of excessive beam warpage, just have a plan to deal with this if it does happen.

    As for not being bad, it is often the details that make or break a design. How that is all welded up and how the fit is made to the bearings are very significant. From all appearances you will need a machine shop to support machining the mounting surfaces for the linear bearings. If that thought has already been considered then you are OK. Otherwise I would build in a solution for mounting the gantry true to the linear bearings.



  8. #44
    Registered
    Join Date
    Mar 2011
    Location
    USA
    Posts
    129
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by wizard View Post
    Not bad!

    As for the steel beam you might try seeing if you have a local steel supplier to industry. Around here that might be Klien, Ryerson and a couple of others that escape my mind. The idea is to get the best price possible for the beam.

    The primary problem with beam thickness selection is suitable thread holding capability. That is after you drill and tap the beam you want confidence that the threads will not strip out. Depending upon the rails being used you may be using 5 or 6 millimeter screws to fasten the rails to the beam. In an ideal world you would want at least 1.5 times the screw diameter in the beams thickness. Unfortunately that leads to a heavier beam than might actually be required from the deflection standpoint.

    Note that all welding you do will add to beam distortion. How much depends on many factors but good fit up makes a big difference. You don't want to weld up your X rods in loose fitting holes for example. I tend to prefer plates welded into the beams with weld beads on all four walls, especially on thinner walled beams. Again though, you do run the possibility of excessive beam warpage, just have a plan to deal with this if it does happen.

    As for not being bad, it is often the details that make or break a design. How that is all welded up and how the fit is made to the bearings are very significant. From all appearances you will need a machine shop to support machining the mounting surfaces for the linear bearings. If that thought has already been considered then you are OK. Otherwise I would build in a solution for mounting the gantry true to the linear bearings.
    I am going to be using CRS plate and CNCrouterparts bearing carriages. I think this will make bearing alignment less of an issue. I already installed them and had them working on that 3x4 be
    Thanks for the feedback



  9. #45
    Gold Member LeeWay's Avatar
    Join Date
    Jun 2004
    Location
    United States
    Posts
    6618
    Downloads
    2
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    In the same vein as the gantry you have chosen was not really sufficient to do the job without some error, the larger options you are looking at now are probably way too large for roller skate bearing trucks and steel flat bar as the guides.
    Somewhere in the middle would probably have been fine.
    There is no need for such a large beam that adds way too much weight to sub standard linear motion designs like the skate bearing on flat bar. I do use such a machine, but not as a main router. Not with such a large heavy beam either.
    You will be having tolerance and wear issues far sooner and more often that you would have with a lesser weight gantry or better linear guides.
    If you are going to stay with the skate bearings, I would probably just add a piece of angle iron to the back of the original gantry design for a little extra support. It will help some with both fex up and down as well as twist without adding excessive weight. Face the angle outward and you could use the outboard side to carry the echain and cable while giving the beam a larger purchase on the gantry supports.

    Lee


  10. #46
    Registered
    Join Date
    Mar 2011
    Location
    USA
    Posts
    129
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by LeeWay View Post
    In the same vein as the gantry you have chosen was not really sufficient to do the job without some error, the larger options you are looking at now are probably way too large for roller skate bearing trucks and steel flat bar as the guides.
    Somewhere in the middle would probably have been fine.
    There is no need for such a large beam that adds way too much weight to sub standard linear motion designs like the skate bearing on flat bar. I do use such a machine, but not as a main router. Not with such a large heavy beam either.
    You will be having tolerance and wear issues far sooner and more often that you would have with a lesser weight gantry or better linear guides.
    If you are going to stay with the skate bearings, I would probably just add a piece of angle iron to the back of the original gantry design for a little extra support. It will help some with both fex up and down as well as twist without adding excessive weight. Face the angle outward and you could use the outboard side to carry the echain and cable while giving the beam a larger purchase on the gantry supports.
    OK . So why do you think the skate bearing trucks are not strong enough? Even if the gantry is 150 lbs that is only 18.75 lbs on each bearing.(8 bearings supporting the load). A person skating on these bearings is applying a lot more weight than that. Maybe I don't understand something?



  11. #47
    Gold Member LeeWay's Avatar
    Join Date
    Jun 2004
    Location
    United States
    Posts
    6618
    Downloads
    2
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    Not necessarily the strength of the bearings. That flat bar is cold rolled steel. It will wear depending on a lot of factors, but weight is definitely one of the main contributors.
    Also a human skating has very little similarity to the forces the bearing will see on a cnc machine.
    I have had to replace a few of the skate bearings over the years. Not hard or expensive, but they do wear out.

    Lee


  12. #48
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    United States
    Posts
    32944
    Downloads
    0
    Uploads
    0

    Default Re: I may have under sized my gantry beam.

    OK . So why do you think the skate bearing trucks are not strong enough? Even if the gantry is 150 lbs that is only 18.75 lbs on each bearing.(8 bearings supporting the load). A person skating on these bearings is applying a lot more weight than that. Maybe I don't understand something?
    Ball bearings are not designed and were never intended to be used like that. They are designed to be a snug fit in a round hole, where the loading is evenly distributed around the fully supported outer race.
    When the bearing is being used as a rolling "guide", it doesn't take that much force to deform the outer race, which can cause binding, and lead to failure.

    It's a decent low cost system, but nowhere near "real" linear bearings.

    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)


Page 4 of 7 FirstFirst 1234567 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

I may have under sized my gantry beam.

I may have under sized my gantry beam.