I may have under sized my gantry beam.


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Thread: I may have under sized my gantry beam.

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    Default I may have under sized my gantry beam.

    I am building a 4x8 CNC router. My gantry beam is a 65 inch length of 3x4x.125 steel tube. I am using the CNCrouterparts linear rail so I have bolted and epoxied a length of 4x.250 CRS plate to the 3 inch wide side which is the vertical axis. I am beginning to think that this tube, even with the .250 CRS plate glued to one side may not resist twisting as well as I had hoped.
    I am hoping to put a 2.2kw spindle on it.
    So I have two questions.
    Is this beam strong enough?
    If not, would welding a length of 2.5x2.5x.375 steel angle across the rear vertical surface fix the issue?
    See attachment.
    ThanksI may have under sized my gantry beam.-gantry-jpg

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    Attached Thumbnails Attached Thumbnails I may have under sized my gantry beam.-gantry-jpg  
    Last edited by tkms002; 12-14-2018 at 03:19 PM. Reason: new drawing


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

    It is likely marginal but a lot depends on additional information. One piece is what do you expect to machine The second is how high are you in Z. Perhaps most important is what are your expectations out of this machine.

    As for the angle iron if you do have a problem I wouldn’t try to correct it this way. Most likely I would just buy another beam of larger cross section. In any event I wouldn’t stress over it until you have considered how the machine will be used. I can see a machine with such a gantry beam as being usable in a number of circumstances. However if your goal is to push the machine hard in difficult materials and at the same time expect high quality you likely will not be happy.



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

    OK I have about 6 inches travel in my z axis. I want to route aluminum but I wouldn't mind building a raised table for this to reduce the z twisting radius.
    If that is no good, My beam needs to be 3 inches in the vertical axis but could be larger than 4 inches in the horizontal. How thick of material do
    I need to make this work?
    Thanks



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    Gold Member Jim Dawson's Avatar
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    Default Re: I may have under sized my gantry beam.

    As I recall a MultiCam 5x10 router has a 6x10x0.25 wall gantry beam. My 4x8 router had a 10x10x0.375 wall gantry beam. Both have about 6 inch Z

    Not sure why you are limited to 3 inch in the vertical, you could always space the rail off of the beam a bit for clearance if needed.

    Jim Dawson
    Sandy, Oregon, USA


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

    I probably would have gone with a thicker material, but why not try it as-is? You might be ok with it.

    If it does let you down, then you’ll be able to interpret better what is wrong and then apply a better, more directed fix.




    Sent from my iPhone using Tapatalk



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

    You could possibly reinforce the beam with a X pattern of material down the inside of the existing beam.



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    Gold Member LeeWay's Avatar
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    Default Re: I may have under sized my gantry beam.

    It will flex and flex alot. Especially in the middle. It isn't really worth the effort to try and beef it up. It would be fine for a plasma cutter, but not for a machine with cutting forces. I don't think twist is the only concern. Up and down flexing would be just as bad.
    I would honestly start over.
    I have about a 5' wide gantry on my plasma cutter. It also uses a die grinder for engraving. I have used it to machine polycarbonate before as well. While I did get usable results, they were not perfect. The depth was a little hard to control and required a finish pass. I was using straight flute bits too. If I were to use a cutter with a helix, it would actually push or pull the tool deeper than wanted.
    My gantry beam is 3" x 3" aluminum extrusion with the 1/4" x 4" flat steel bar bolted to it. It works great at plasma cutting and engraving. Lots of easy speed.
    Not optimal as a router.

    I don't think I would rely on adhesive only for a structural joint either. I would back it up with at least a few mechanical fasteners. Especially given that this beam will be flexing.

    Lee


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    Default

    Well I have to admit I never thought that .25x4 plate would flex in the verticle. CNCRouterparts makes their 4x8 on a 3x3 chunk of 8020. Maybe that is a lot stronger. I looked at speedy metals for a 5x5x.25 tube and the price was over $300. I have to find a cheaper way. Thanks for all your input.



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

    CNCRouterParts uses a 160mmx80mm about 6inch x 3inch aluminum extrusion.



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

    Cost can certainly be an issue. You might want to proceed with the build and upgrade later.
    You can setup an easy test to see what you have. Support the beam on both ends.
    Put a dial indicator in the middle. Then add a little weight. I think you will be surprised by how much movement you see.

    Lee


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    Community Moderator ger21's Avatar
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    Default Re: I may have under sized my gantry beam.

    Speedy metals is expensive.
    You can get a 3/16 4x6 for a lot less.
    https://www.onlinemetals.com/merchan...41&top_cat=849

    Regardless, you'll want to reinforce the beam, maybe like this one.
    https://www.cnczone.com/forums/cnc-w...ml#post1689518

    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: I may have under sized my gantry beam.

    Quote Originally Posted by nlancaster View Post
    CNCRouterParts uses a 160mmx80mm about 6inch x 3inch aluminum extrusion.
    the new ones do, yes. But at the school I mentored a robotics club at we bought one several years ago (a 4848) and it has a 3x3 gantry beam.



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I may have under sized my gantry beam.

I may have under sized my gantry beam.