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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > Deciding the CNC frame for milling large workpieces ?
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  1. #1
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    Red face Deciding the CNC frame for milling large workpieces ?

    Hi all,

    I want to build one CNC by assembling only.
    Materials: stainless steel and hard materials like titanium.
    Weight of the Materials will go maximum upto 300kg.
    Table size : 1000*1000mm

    which type of frames give best accuracy possible?


    Ex: https://www.cnc-step.com/cnc-router-...ws-1400x800mm/

    I have not seen milling ss steel in the above configuration. I see mostly in dovetail configuration , why?

    Which frame type will suit my application?

    Best Regards
    Nara

  2. #2
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    Re: Deciding the CNC frame for milling large workpeices ?

    Hi Nara - The machine you linked to will not cut SS or Ti. The link is to a router not a mill. But to cut 300kg of SS or Ti you will need to make a fixed gantry (or bridge or portal or double column all depends on who you talk to) machine with a moving table so you will need a 2000mm long machine. To cut materials like SS and Ti you need an exceptionally stiff machine. I suggest you find a commercial machine that does what you want so you can understand what it looks like and what power is needed, what tooling is needed etc. Most machine builders now will make machines with rails not dovetails. If you look you will find many machines like this.



    or https://www.snkcnc.com/cnc-machining-center-snk-1060b

    Cheers Peter

  3. #3
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    Re: Deciding the CNC frame for milling large workpeices ?

    Zero chance of what you want.

    There are no off the shelf parts that you can assemble to have a machine that will cut SS with a 1m cutting area.
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  4. #4
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    Re: Deciding the CNC frame for milling large workpeices ?

    A so-called double column mill, with moving table, is the most rigid solution.

    Cannot be done for milling steel in 350 kg.

    I built one.
    And my table alone is 200 kg in mass, for 1600x600 mm in table size.
    Total mass is 2000 kg, approx.
    All in steel, all bolted, linear guides, ISO30 spindle, automatic toolchange via pnematic drawbar.

    Y axis == 400 kg.
    Columns 270 kg each, 250 x 400 x 1400 mm with 12 cm risers (35 kg each), x 2, 540 kg approx.

    The vertical head is about 500 kg, and is supported by 2 gas springs, of 2500N or 250 kgf push force, each.

    Rigidity about 0.03 mm deflection under 87 kgf load, so == 30 microns / 870 N, or == 29 N / um.

    But I have 500 mm max vertical movement, travel, with 1000 mm tall linear rails, and 500 mm tall edge-edge contact surfaces on the rails.
    Rails are 35 mm HIWIN, 6 of, on z, with 12 blocks.
    Theoretical load 4000 kg per block, x 12, or about 48 metric tons rated load capacity on z.

    You have to have that, to get the z axis deflection under control.
    I tried 5 times, in 10 years, to get it right.

    The rigidity improved from about 0.28 mm to 0.03, or about ten times, over 5 iterations.

  5. #5
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    Re: Deciding the CNC frame for milling large workpeices ?

    Quote Originally Posted by peteeng View Post
    Hi Nara - The machine you linked to will not cut SS or Ti. The link is to a router not a mill. But to cut 300kg of SS or Ti you will need to make a fixed gantry (or bridge or portal or double column all depends on who you talk to) machine with a moving table so you will need a 2000mm long machine. To cut materials like SS and Ti you need an exceptionally stiff machine. I suggest you find a commercial machine that does what you want so you can understand what it looks like and what power is needed, what tooling is needed etc. Most machine builders now will make machines with rails not dovetails. If you look you will find many machines like this.

    https://www.youtube.com/watch?v=sg7pK6RluLo

    or https://www.snkcnc.com/cnc-machining-center-snk-1060b

    Cheers Peter
    Thanks a lot peter.I will look into those machines and come back. I have good understanding of the servos to drive the axis and other electricals. But not much about the frames.

    You really touched the point. Moving the table for 2000mm. Can't the table be fixed and the spindle move along the table like the router . are there no such frames in milling ss steel / titanium? what is the exact challenge there? I know its not possible but want to exactly know the reason .

    I just heard that direct drive spindles can make such milling in router/open frame configuration?

    Thanks once again Pete. I will update my further search results.

    Best Regards
    Nara

  6. #6
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    Re: Deciding the CNC frame for milling large workpeices ?

    Quote Originally Posted by pippin88 View Post
    Zero chance of what you want.

    There are no off the shelf parts that you can assemble to have a machine that will cut SS with a 1m cutting area.
    thanks for the reply Pippin. I even intend to make such frame. I just want to know what is the right design choice. I will do simulation/FEA analysis and then proceed.

    Best Regards
    Nara

  7. #7
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    Re: Deciding the CNC frame for milling large workpeices ?

    Quote Originally Posted by hanermo View Post
    A so-called double column mill, with moving table, is the most rigid solution.

    Cannot be done for milling steel in 350 kg.

    I built one.
    And my table alone is 200 kg in mass, for 1600x600 mm in table size.
    Total mass is 2000 kg, approx.
    All in steel, all bolted, linear guides, ISO30 spindle, automatic toolchange via pnematic drawbar.

    Y axis == 400 kg.
    Columns 270 kg each, 250 x 400 x 1400 mm with 12 cm risers (35 kg each), x 2, 540 kg approx.

    The vertical head is about 500 kg, and is supported by 2 gas springs, of 2500N or 250 kgf push force, each.

    Rigidity about 0.03 mm deflection under 87 kgf load, so == 30 microns / 870 N, or == 29 N / um.

    But I have 500 mm max vertical movement, travel, with 1000 mm tall linear rails, and 500 mm tall edge-edge contact surfaces on the rails.
    Rails are 35 mm HIWIN, 6 of, on z, with 12 blocks.
    Theoretical load 4000 kg per block, x 12, or about 48 metric tons rated load capacity on z.

    You have to have that, to get the z axis deflection under control.
    I tried 5 times, in 10 years, to get it right.

    The rigidity improved from about 0.28 mm to 0.03, or about ten times, over 5 iterations.
    Hi hanermo,

    thats truly inspiring and motivating. 5 tries in 10 years. Incredible.

    I meant my maximum load on table for ss steel is 350kg.

    How did the rigidity improvement happen in 5 tries? where were things getting corrected ?

    I will happy if I can buy few parts which are easy to ship as you said you build them.
    Did you try direct drive spindles?

    Thanks a ton for letting me know you did it. I felt i was alone in this boat.

    Best Regards
    nara

  8. #8
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    Re: Deciding the CNC frame for milling large workpeices ?

    Hi Nara - There are moving column machines but the 1000mm span is the issue. Rare to get a single column machine over 600mm. What you want to do is not impossible but commercial machines cost $500,000USD perhaps $1M to do a 1000x1000 at a commercial accuracy. Look at any of the commercial machines Mazak, HAAS Mori seiki and they weigh several tonnes and have 100,000 hrs of development time into them. Mazak VMC small machine is 500x1000mm. Their moving column machine is 3000x800mm and the bed is fixed. You are on a tough, costly and long journey. Good Luck. Better off to buy a small used machine and improve it. If you have jobs that require 1000x1000 better to contract it to a large machine shop.

    Its all possible "the exact challenge" is to make a machine that is very stiff say 150um/N that does not cost a small fortune. Unfortunately it will cost a small fortune. You can make a high rail design, a moving bed design, a fixed bed design, a lifting gantry design, a bridgeport design a moving gantry design. All can be made to work but the machine will be huge to do what you want. Again find commercial machines and get an understanding of how they look and work. Your machine will look like one of them, take years to build and improve and cost a lot. Sounds like fun if you have the $$$. Peter

  9. #9
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    Re: Deciding the CNC frame for milling large workpeices ?

    Hi Nara - I meant 150N/um not the other way round! Look up the Maximus thread its all about machine stiffness....Cheers Peter

  10. #10
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    Re: Deciding the CNC frame for milling large workpeices ?

    Hi Nara - something like this. Peter
    https://www.lvcnc.com/tc-2013l-gantr...g-machine.html

  11. #11
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    Re: Deciding the CNC frame for milling large workpeices ?

    Quote Originally Posted by peteeng View Post
    Hi Nara - I meant 150N/um not the other way round! Look up the Maximus thread its all about machine stiffness....Cheers Peter
    Going through the Maximus thread .

    thanks peter. I will update my search soon.

  12. #12
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    Re: Deciding the CNC frame for milling large workpeices ?

    Quote Originally Posted by hanermo View Post
    A so-called double column mill, with moving table, is the most rigid solution.

    Cannot be done for milling steel in 350 kg.

    I built one.
    And my table alone is 200 kg in mass, for 1600x600 mm in table size.
    Total mass is 2000 kg, approx.
    All in steel, all bolted, linear guides, ISO30 spindle, automatic toolchange via pnematic drawbar.






    Y axis == 400 kg.
    Columns 270 kg each, 250 x 400 x 1400 mm with 12 cm risers (35 kg each), x 2, 540 kg approx.

    The vertical head is about 500 kg, and is supported by 2 gas springs, of 2500N or 250 kgf push force, each.

    Rigidity about 0.03 mm deflection under 87 kgf load, so == 30 microns / 870 N, or == 29 N / um.

    But I have 500 mm max vertical movement, travel, with 1000 mm tall linear rails, and 500 mm tall edge-edge contact surfaces on the rails.
    Rails are 35 mm HIWIN, 6 of, on z, with 12 blocks.
    Theoretical load 4000 kg per block, x 12, or about 48 metric tons rated load capacity on z.

    You have to have that, to get the z axis deflection under control.
    I tried 5 times, in 10 years, to get it right.

    The rigidity improved from about 0.28 mm to 0.03, or about ten times, over 5 iterations.
    You meant all casting material is steel ?


    what maximum stainless steel grade could you mill?

    which cast iron grade would be good for such double column castings? I am also considering stainless steel tubes with epoxy granite filling?

    when vertical head is only 500kg , why 12 blocks on z-axis? Higher weight on z-axis will increase rigidity. How did you load those 12 blocks when head is only 500kg.

    which HIWIN series of linear guides did you use for all axis?

    Hope to receive some help in these clarifications.



    thanks in advance.

    Warm Regards
    Nara

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