1. #1
    kim's Avatar
    Lives in PaTong, Thailand. Last Activity: 23-05-2016 Has been a member for 0-1 years. Has a total post count of 1.
    Hey guys,

    IŽam planing a CNC Machine with steel profiles and plates on "20mm profile linear rails" and stuck with the needed loads for the Stress Analysis in "Autodesk Inventor 2016".
    (German guy, so donŽt smile about my lousy English)

    What i need?
    Workspace X >1000, Y > 800, Z >270mm
    + 4.-Axis

    What i will do?
    Cutting max Plywood in 1000x800 in 2D
    Cutting Wood in 2.5D
    Aluminium and Brass in smaller Parts, let it be 200x100 max, high accuracy

    (on this step i dont care about dimensions of stepper motors or ball screws (2005 in head))

    I construct the machine with "Autodesk Inventor" and take the build-in Stress-Analysis for testing it.
    At the moment i run the Stress-Analysis with 2000N horizontal on the motor-bracket... and got max 0.08mm Displacement :-( For me its sounds a lot....
    The last weeks i do a lot of research in internet and study a lot of machine-designs from other people: 2 Plates, 1 Aluprofile... BAMM... seems to work!
    And i calculate and try and calculate again, and at the end i stuck with a 300kg starship and nearly 0.1mm Displacement (aside tolerance of linear rails and ball screws) :-((
    Also the high rails at the table are a Result of this Stress-Analysis... i donŽt like it.

    So my questions, before i run more in the wrong direction:
    1. if you calculate your machines, whats the max. load for the motor-bracket/tool you calculate with?
    (Alu, 3mm Tool, 6mm Tool for first cut, no rush, no competition)

    2. DIY Gantry machines in general... 0.08mm Displacement is what you can reach with a moving gantry, or can it be better without more weight?

    3. or may the Software is a crap, the Stress-Analysis is more or less a inaccurate overview and the shown Design below will be better than 0.1mm Displacement?

    Thanks for answering...

    the machine
    Click image for larger version. 

Name:	Gesamt v3 - sleeping.bmp 
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ID:	18433

    Stress-Analysis: Gravity + 1000N vertical (spindle, motors, cable, ball screws and so on), 2000N horizontal on motor-bracket
    Click image for larger version. 

Name:	Gesamt v3 - 2000N.jpg 
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ID:	18434Click image for larger version. 

Name:	Gesamt v3 - 2000N back.jpg 
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ID:	18436

    Y/Z Axis: the Rails for the z-axis are placed on 40x40mm steel-plates to give space for the 2005 ball screws (60mm nuts)
    Click image for larger version. 

Name:	Gesamt v3 Top.jpg 
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ID:	18437

    some Details of Y- and Z-Axis, all made from 12mm steel plates
    Click image for larger version. 

Name:	Y - Front.jpg 
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ID:	18440Click image for larger version. 

Name:	Y - Back.jpg 
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ID:	18439Click image for larger version. 

Name:	Motorplatte v3 - back.jpg 
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ID:	18438Click image for larger version. 

Name:	Motorplatte v3 - front.jpg 
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ID:	18435
    Last edited by kim; 10-05-2016 at 09:01 PM.

  2. #2
    Those forces seem excessive for the stress calcs. I would expect closer to 200N for steel not 2000N. Even less for aluminium. See this thread for more info and where that number comes from. Obviously machining forces will vary but this gives a guide
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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