Gantry sides and torsion box questions


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    Member Biggs427's Avatar
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    Default Gantry sides and torsion box questions

    I'm in the process of designing my second CNC.

    My initial plan was to build a torsion box for the 600mm (23.62in) gantry with 1/2 baltic birch in fact 11.5mm. The torsion box (the yellowish part on image) would be 600mm x160mmx80mm.

    I would attach a 3/4 600mmx195mm on the front to bolt the profile rail for the Y axis.

    Here's the unfinished CAD of my design.


    For the sides I was thinking of laminating two 3/4 birch ply together that would give me 35mm sides.

    I'm planning to use the Makita 1.25HP small router I already have on my current CNC

    1 - Is this a valid design or is it flawed?

    2 - Will 35mm sides be strong enough?

    3 - What would be the best way to attach the sides to the gantry beam?

    I'm mostly cutting wood and dome 1/8 alu sheets with my current CNC and want to do the same with this one.

    Thanks

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    Attached Thumbnails Attached Thumbnails Gantry sides and torsion box questions-cnc-2-0-front-jpg   Gantry sides and torsion box questions-cnc-2-0-back-jpg  


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    Default Re: Gantry sides and torsion box questions

    Quote Originally Posted by Biggs427 View Post
    I'm in the process of designing my second CNC.

    My initial plan was to build a torsion box for the 600mm (23.62in) gantry with 1/2 baltic birch in fact 11.5mm. The torsion box (the yellowish part on image) would be 600mm x160mmx80mm.
    I'd use thicker panels for the outside walls of the torsion boxes. Mainly for screw holding capability.
    I would attach a 3/4 600mmx195mm on the front to bolt the profile rail for the Y axis.
    I'm hoping your axis arrangement is the same as the one I try to maintain that is X,Y & Z from bottom to top.
    Here's the unfinished CAD of my design.
    For the sides I was thinking of laminating two 3/4 birch ply together that would give me 35mm sides.
    For the uprights or supports for the Y axis gantry beam. You might get additional stiffness with a boxed design or go to 3 layers of plywood. I have to ask though why a second machine? Do you have shortcomings on the original you are trying to correct? If so highlighting those issues may make it easier for people to focus on design issues for those problems.
    I'm planning to use the Makita 1.25HP small router I already have on my current CNC

    1 - Is this a valid design or is it flawed?
    Seriously all machines are flawed, nothing is perfect machine tool wise

    Given that I see some of your linear bearings appear to be mounted such that they aren't supported well. The X axis being pretty obvious.

    The gantry box section looks to be a bit thin too. Frankly I'd look into steel for the gantry beam. By the time you build up a strong wood gantry beam you will be close to the expense of a square steel tube.
    2 - Will 35mm sides be strong enough?
    It depends upon what you are trying to correct. Physically it is easy to do a three panel laminated ion and not worry about it.
    3 - What would be the best way to attach the sides to the gantry beam?
    Well this is always a challenge. You could integrate the uprights into the gantry beam design but this isn't efficient when it comes to material usage. Another option would be to do an upright that is T like in cross section and use the upper T as a flange to connect to the beam. The reality is there is likely to be a million ways to do this.
    I'm mostly cutting wood and dome 1/8 alu sheets with my current CNC and want to do the same with this one.

    Thanks
    I don't see a huge problem with your design beyond what is outlined above. Frankly I'm not a fan of wood machines to machine metal as I generally expect to use some sort of lube / coolant. However if you are machining dry with little issues right now don't let me stop you.

    In any event you need to outline why you want to build a second machine and what are the problems on the first you want addressed. At first glance I'm concerned about rail placement and gantry size.



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    Default Re: Gantry sides and torsion box questions

    ...I have to ask though why a second machine? Do you have shortcomings on the original you are trying to correct? ...
    My first design was mainly an alpha version and there were lots of problems: "Not so square" gantry, drawer slides as X and Y linear rails, 425mmx425mm working area, Nema 17 stepper and so on.

    I've used this first CNC as a learning tool for electronic and for how a CNC is working mechanically. The only thing I'm gonna use from my old CNC is the Z axis which is the same as my design.

    I choose wood as I work in a millwork so material and wood working tools are easy to come by.

    When I machine alu I'm using some kind of bucket made of plastic film to keep the fluid from the MDF sacrificial board but that method is far from perfect and I have to change the sacrificial board earlier that if I'd machine dry.

    I might have access to a metal milling machine so that might solve that problem. Will take longer to build as I can't do the metal working myself but at least a metal frame will have less problem with fluid.

    I'm going to continue exploring, design, etc. This part is as much fun as using the machine.

    Thanks for your input!



  4. #4

    Default Re: Gantry sides and torsion box questions

    I agree with Wizard regarding additional stiffness for gantry sides. Just finished my torsion box design. While it's exceptionally rigid, there is a little flex in side loads due to the fact that I only used one thickness of 3/4" MDF for gantry sides. If I redesign it, I'll make gantry sides a torsion box as well.

    Here's a basic drawing of what I did. You'll notice two layers of MDF in the top drawing. I built it with only one thinking I'd only need one. I needed two.



    Quote Originally Posted by wizard View Post
    I'd use thicker panels for the outside walls of the torsion boxes. Mainly for screw holding capability.

    I'm hoping your axis arrangement is the same as the one I try to maintain that is X,Y & Z from bottom to top.

    For the uprights or supports for the Y axis gantry beam. You might get additional stiffness with a boxed design or go to 3 layers of plywood. I have to ask though why a second machine? Do you have shortcomings on the original you are trying to correct? If so highlighting those issues may make it easier for people to focus on design issues for those problems.

    Seriously all machines are flawed, nothing is perfect machine tool wise

    Given that I see some of your linear bearings appear to be mounted such that they aren't supported well. The X axis being pretty obvious.

    The gantry box section looks to be a bit thin too. Frankly I'd look into steel for the gantry beam. By the time you build up a strong wood gantry beam you will be close to the expense of a square steel tube.

    It depends upon what you are trying to correct. Physically it is easy to do a three panel laminated ion and not worry about it.

    Well this is always a challenge. You could integrate the uprights into the gantry beam design but this isn't efficient when it comes to material usage. Another option would be to do an upright that is T like in cross section and use the upper T as a flange to connect to the beam. The reality is there is likely to be a million ways to do this.


    I don't see a huge problem with your design beyond what is outlined above. Frankly I'm not a fan of wood machines to machine metal as I generally expect to use some sort of lube / coolant. However if you are machining dry with little issues right now don't let me stop you.

    In any event you need to outline why you want to build a second machine and what are the problems on the first you want addressed. At first glance I'm concerned about rail placement and gantry size.


    Attached Thumbnails Attached Thumbnails Gantry sides and torsion box questions-overview-jpg  


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    Default Re: Gantry sides and torsion box questions

    The one nice thing about MDF is that you can glue additional panels onto the gantry supports without much issue. You don't need to cover the full panel to mprive things a bit.

    Quote Originally Posted by fretman_2 View Post
    I agree with Wizard regarding additional stiffness for gantry sides. Just finished my torsion box design. While it's exceptionally rigid, there is a little flex in side loads due to the fact that I only used one thickness of 3/4" MDF for gantry sides. If I redesign it, I'll make gantry sides a torsion box as well.

    Here's a basic drawing of what I did. You'll notice two layers of MDF in the top drawing. I built it with only one thinking I'd only need one. I needed two.





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    Default Re: Gantry sides and torsion box questions

    Quote Originally Posted by Biggs427 View Post
    My first design was mainly an alpha version and there were lots of problems: "Not so square" gantry, drawer slides as X and Y linear rails, 425mmx425mm working area, Nema 17 stepper and so on.
    I'd identify the major weaknesses you want to fix and make sure your new design addresses them.

    By the way one issue with high precision linear rails on wood based machines is dealing with distortions of the machine with changes in the weather.
    I've used this first CNC as a learning tool for electronic and for how a CNC is working mechanically. The only thing I'm gonna use from my old CNC is the Z axis which is the same as my design.

    I choose wood as I work in a millwork so material and wood working tools are easy to come by.
    Wood is perfect fine if it is used to address dry machining. Not so good with stuff that that needs coolant / lube.
    When I machine alu I'm using some kind of bucket made of plastic film to keep the fluid from the MDF sacrificial board but that method is far from perfect and I have to change the sacrificial board earlier that if I'd machine dry.
    It becomes an issue and the more aluminum you do the greater the risk of damaging your machine.
    I might have access to a metal milling machine so that might solve that problem. Will take longer to build as I can't do the metal working myself but at least a metal frame will have less problem with fluid.
    One thing to consider is that you can cut aluminum on most wood working machines. I generally suggest steel as it is so much cheaper but it is worth considering aluminum if you have access to a huge amount of wood working tools already. Even then there is much you can do with steel if you are willing to drill a lot of holes.
    I'm going to continue exploring, design, etc. This part is as much fun as using the machine.
    It is a good distraction from the work day too! You can do a lot of design work mentally and nobody is the wiser.
    Thanks for your input!
    Only you know how much aluminum you will be doing on the machine. Given that, if it is a considerable amount, I'd strongly suggest a build out of metal. At least for part of the machine. You will be putting a lot of work into this machine and the last thing you want is bloated MDF due to a fluid leak or whatever.



  7. #7

    Default Re: Gantry sides and torsion box questions

    Yea...I actually plan on bolting on a steel angle stiffner to each side...that ought to do the trick.

    Quote Originally Posted by wizard View Post
    The one nice thing about MDF is that you can glue additional panels onto the gantry supports without much issue. You don't need to cover the full panel to mprive things a bit.




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    Default Re: Gantry sides and torsion box questions

    Still designing my gantry.

    I'm questioning my self on how to attach my profile rails to the gantry for Y and the base torsion box for X.

    I want to make sure that the surface where the rails will be is straight so I'm gonna use Epoxy. To make sure the bolts that holds the rails have a good thread material, I was thinkning of putting a steel flat bar on a 17.5mm BB piece that would be grooved and the laminate the BB piece to my the torsion box using epoxy.

    Just like this:
    Gantry sides and torsion box questions-gantry-jpg

    It would be easy to tap the steel bar with the M4 tap to attach the HGR15 rails.

    Does it make sense? Anything I'm missing?



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    Default Re: Gantry sides and torsion box questions

    You'll probably need to seal it with epoxy before pouring, as it'll want to soak in somewhat.
    This is similar to what I'm doing. I used phenolic strips epoxied to the wood, and machined it flat.
    For my Z axis, I epoxied hex nuts from the back side.
    For my gantry, I plan on either epoxying nuts from the back before assembly, or using round bar in holes, which I'd drill and tap from the front.

    http://www.cnczone.com/forums/cnc-wo...ml#post1010295

    http://www.cnczone.com/forums/cnc-wo...ml#post1168468

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

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

    (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: Gantry sides and torsion box questions

    The sealing is done with just epoxy et something else?

    Thanks



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    Default Re: Gantry sides and torsion box questions

    Yes, epoxy is probably best.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

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

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


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