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IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > Designing my first 3Axis cnc router, able to cut alu.
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  1. #1
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    Designing my first 3Axis cnc router, able to cut alu.

    So me and a couple of friends decided that we want to design a 3 Axis cnc router that is able to cut aluminium.

    Components i have found, and consider using.
    Nema 23 340oz stepper engines (Nema 23 CNC Stepper Motor 2.4Nm(340oz.in) 1.8A 23HS41-1804S - US$)
    16mm lead screws, 1000mm, 800mm and 300mm.
    12mm linear guide for Y and Z axis, 16mm linear guide for for X axis. (Picture further down of the linear guides i want to use(not going with the ones in the 3D model)
    For the frame i have used 50x50mm alu extrusions.

    Does anyone have anything to say about the dimensions on the lead screws, linear guides and engines. Basically i wonder if it is strong enough to cut aluminium. And if not, please point me in the direction of some useful info on the subject.

    This is the basic design we want. The final design will most likely look a lot different, but this is our starting point.

    Dimensions:

    The type of linear guide i am considering using.

  2. #2
    Community Moderator ger21's Avatar
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    Anything will cut aluminum.
    The question, is how well do you want to cut aluminum?

    Basically, what you have won't even cut wood all that well.

    The extrusions are too small, and should be steel.
    Round shafts and bearings are not all that rigid.
    The Z axis hangs down too far.
    The sides are much too tall. As your Z axis carriage moves side to side, those tall sides will sway back and forth when the Y axis changed direction.
    Gerry

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

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    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. #3
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    I don't have any numbers on the accuracy we want, as accurate as we can get it without going overboard on time and cost.

    For the linear bearings, something like the one in the 3D drawing would be the way to go?

    As i said the design was basic, so strength/rigidity has not been adressed. But thanks for the input.

  4. #4
    Community Moderator ger21's Avatar
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    I would consider profile linear rails like THK or Hiwin mandatory for an aluminum cutting 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)

  5. #5
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    Ger21 said it.

    Increase section sizes 2x.
    100x100 or 150x150 mm beams, in steel. => 50x more stiff, and same cost.
    Thick wall - thicker is better. Heavier/thicker wall is better (solid would be fine, as an example).
    Use crossed plates bolted onto beams for rigidity, or double verticals, with 2-4x D as separation.
    Ie 100x100x5 mm verticals. Another set outisde, with 2-300 mm between them. Bolt flat (10 mm is fine) plate to them, in x and y directions.

    Result will be 1000x more stiff, and will mill alu well, even at industrial forces.

    Machining alu needs == 20-50 kgf force.
    Imagine standing at the tooltip, with machine on its side.
    Must not bend 0.03 mm or more.

    To conceptualise, in your mind, what you need:
    A good mill (metals, steel) resists == 10.000 kg crosswise force without damage, indefinitely.
    Alu router, 1000-2000 kg (0.5 hp-1 hp ballpark).
    Actual force == 50 kg.
    You need 20:1 margin vs yield/break/failure point for good results.

    Example:
    My mill generates 3000 kgf push force at ballscrews. It could lift a full semi truck.
    You need about 1/10 for light alu stuff.


    Cost is minimal.

    Forget the linears proposed.
    Use profiled linear guides like hiwin, thk.
    20 mm (or up) size, heavy preload if you can get it reasonably.
    (15 mm is strong enough - thats not the point. Fab wont be perfect, and linears will increase rigidity easier than anything else).

    Motors wont matter. They will be fine as proposed.

    I made a VMC mill to do steel.
    I use 35 mm linear guides.
    Theoretical load capacity is = 32.000 kg.
    Actual, about 2000 kg (machine wont get damaged at 10.000 kg, It wont work well, though (inertia matching).
    Illustrates what I mean.

    Advise is based on experience, and having done this, and industrial cnc factory training.
    And 15.000 hours experience, full time, mostly, since 2003.
    0.05 €.

  6. #6
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    Thanks for the info.

  7. #7
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    Quote Originally Posted by Pettersen View Post
    So me and a couple of friends decided that we want to design a 3 Axis cnc router that is able to cut aluminium.
    What type of aluminum? Also your vertical clearances are all out of whack for the size of your structural members.
    Components i have found, and consider using.
    Nema 23 340oz stepper engines (Nema 23 CNC Stepper Motor 2.4Nm(340oz.in) 1.8A 23HS41-1804S - US$)
    16mm lead screws, 1000mm, 800mm and 300mm.
    12mm linear guide for Y and Z axis, 16mm linear guide for for X axis. (Picture further down of the linear guides i want to use(not going with the ones in the 3D model)
    For the frame i have used 50x50mm alu extrusions.
    Steel is so much cheaper as to make aluminum a rich mans decision. 50 mm square steel is doable for smaller machines aimed at wood panels but is a little spindly for any aluminum work though should never be considered for a gantry.
    Does anyone have anything to say about the dimensions on the lead screws, linear guides and engines. Basically i wonder if it is strong enough to cut aluminium. And if not, please point me in the direction of some useful info on the subject.
    People have already suggested profile rails. This is not a bad idea, however profile rails won't do much good on a weak frame. In other words if you can't build a decent frame there is little sense in putting profile rials on the machine. Frankly you can also update to profile rails at a later date.

    If you can't afford to do a decent frame then don't waste money on fancy linear rails. You will be far better off building a frame that can properly support profile rails though.
    This is the basic design we want. The final design will most likely look a lot different, but this is our starting point.
    In a nut shell you really need to nail down expected usage. The reason being expected usage will dictate design. As it is right now your design is a non starter and has way too many structural issues to go forward with.

  8. #8
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    Going to do an analysis in Inventor or Ansys workbench to make shure my new design is strong enough. So if it bends less than 0.03mm with 500N on the tooltip it should be good?
    What force would i need in order to machine steel? (Just out curiosity, would be fun to test out in Inventor/ansys to see what would happen)

    Quote Originally Posted by hanermo View Post

    Machining alu needs == 20-50 kgf force.
    Imagine standing at the tooltip, with machine on its side.
    Must not bend 0.03 mm or more.

    0.05 €.

  9. #9
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    Quote Originally Posted by Pettersen View Post
    Going to do an analysis in Inventor or Ansys workbench to make shure my new design is strong enough. So if it bends less than 0.03mm with 500N on the tooltip it should be good?
    Yes some like that value. There are also lots of factors that come into play and is why I suggested that you need to get a handle on your expectations. The load on a tool can vary dramatically depending upon what you are doing at the time.
    What force would i need in order to machine steel? (Just out curiosity, would be fun to test out in Inventor/ansys to see what would happen)
    You will want a machine that is able to resist at least ten times the force at the tool tip and likely even more. In US terms I'd suggest at least 1500 pounds of force. Many would say that ten times isn't enough either.

    *****************

    Now above I suggested getting a handle on your expectations and maybe expending your knowledge of machining technologies. The actual force on a cutter varies widely depending upon the cutters size and design. In other words a three millimeter diameter cutter has less of an impact than say a 12 mm diameter cutter. Likewise depth of cut and feed rates have a big impact on forces. Also spindle horse power is often a limiting factor on small DIY machines.

    You often see people post images of their machines highlighting the machining of aluminum on very light weight machines. Technically they have done so but it is not the way you would machine aluminum in the real world. Beyond that stiffness impacts the quality of the machined surfaces. It comes back to expectations.

    When you see rule of thumbs here they are generalizations that can lead to a good design. Even with things like commercial milling machines they are offered in a range of robustness.

    In the case of your machine the long Z axis has to be seen as a long lever arm. If you maintain that length you will need to put more design effort into the stiffness of that assembly and the components that support it. Basically that means everything about the design needs to be analyzed. You need to pay special attention too with respect to the types of linear bearings used, how they are mounted and spacing.

  10. #10
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    Re: Designing my first 3Axis cnc router, able to cut alu.

    The Z axis will be a lot shorter that the drawing i posted. In the design i'm working on now there is 225mm from the middle of the gantry to the working surface.

    As for now, the things i would like to make are intake flanges (10mm plate) and velocity stacks (aprox 30-80mm tall), so i could make it even shorter if i need to.

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