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  1. #1
    Junior Member wh33lz's Avatar
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    Default Modelling a twisted square steel bar

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    Okay, havent been around here for a while, but Im fairly handy with ACAD 07, and I spend alot of time modelling traditional Wrought Iron.

    I can create almost any flowing organic shape fairly easily, but Im stuck on how to model a simple twisted bar.

    Imagine a piece of half inch steel square bar, grasped on each end and twisted through its centre axis several times. Thats twisted bar basically.

    I can do it by using edge surf in conjunction with a 3D spline through a set of geometrically placed points, but its clumsy, slow, not geometrically correct and not ideal to use sufaces anyway.

    I just want to extrude a square and twist it on its centre axis a set amount of times over a set amount of distance, Is this possible?

    Any help would be greatly appreciated!

  2. #2
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    Default 3D AutoCAD

    You need to use the sweep command. Draw your profile, select a path and specify the number of twists.....

    ---------------------------------------
    3D AutoCAD Pipework – http://www.HerculeDesign.com

  3. #3
    Junior Member wh33lz's Avatar
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    Default

    Tried that, unfortunately it wont twist along a straight path, it just extrudes as per the standard extrude command, no matter what angle in degrees I tell it to twist at..
    any other ideas guys?

  4. #4
    Super Member chrisdarmanin's Avatar
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    Default

    i managed that with sweep command but for a strange reason it will not take 1800 degrees twist (5 turns or any number of complete turns) but it takes any other angle. very strange indeed
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    Quote by George (AWDC Malta President) about Land Rovers:
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    Translation: You have to attack it with a mallet for no reason at all"

  5. #5
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    Default 3D AutoCAD Loft

    You can also use the LOFT command to make some pretty interesting twisted bars...
    ---------------------------------------
    Pipework & Structural Steel http://www.3DCADMax.com
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  6. #6
    Junior Member wh33lz's Avatar
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    Default

    Quote Originally Posted by chrisdarmanin View Post
    i managed that with sweep command but for a strange reason it will not take 1800 degrees twist (5 turns or any number of complete turns) but it takes any other angle. very strange indeed
    Thats an awesome diagram, exactly what I was after, but unfortunately I must have something fundamentally wrong with my procedure, because it still extrudes straight, even at any angle.

    My procedure is this:

    I draw a 12 x 12 square on the x/y plane >
    Add a line at a set length (eg 750mm) starting from the centre of the square along the z plane>
    Choose the sweep command>
    Select the square>
    Set the twists at any angle other than a full turn (eg 9365 degrees, which is slightly over 26 turns)>
    Select the path (line at 750 long on the z plane)>
    It extrudes straight as a die???

    I obviously doing something wrong.. just cant figure it out?

    edit- Ok i think I figured it out, If the path lies on the same plane as the object to be extruded, ie all on the xy, it works.
    But the angle modifier isnt intuitive at all, if you increase the angle (intuitively adding 360 degrees for each full turn) it starts playing some funny tricks. ie, I tried 19020 degrees over 120 mm and it turned only about 10 degrees, but if I try 2100 degrees over the same distance, I get about 270 degrees. strange indeed.

    I'll endeavour to figure out how this can be manipulated to get the desired result, but all in all it seems odd.

    2nd Edit-
    Ok I tried 270 degrees and get an almost exact result as 2100.

    Im thinking it will only twist through 360 or increments thereof.
    Only way to be sure is try out many different lengths and angles untill I get a controllable procedure.
    Last edited by wh33lz; 14th May 2008 at 05:52 am. Reason: second round of Further experimentation

  7. #7
    Junior Member wh33lz's Avatar
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    Default

    Heres a few twists in 30 degree increments, you can twist at 359 degrees which will give 1 full twist, but thats it. Any more than 359 goes back to 0 degee, then 1 degree etc..

    Only way to get 5 twists over a set distance is divide the distance into 5, twist that section and unite them into a single object.
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  8. #8
    Super Member chrisdarmanin's Avatar
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    Default

    edit- Ok i think I figured it out, If the path lies on the same plane as the object to be extruded, ie all on the xy, it works.
    But the angle modifier isnt intuitive at all, if you increase the angle (intuitively adding 360 degrees for each full turn) it starts playing some funny tricks. ie, I tried 19020 degrees over 120 mm and it turned only about 10 degrees, but if I try 2100 degrees over the same distance, I get about 270 degrees. strange indeed.

    I'll endeavour to figure out how this can be manipulated to get the desired result, but all in all it seems odd.

    2nd Edit-
    Ok I tried 270 degrees and get an almost exact result as 2100.
    i had all those problems

    Heres a few twists in 30 degree increments, you can twist at 359 degrees which will give 1 full twist, but thats it. Any more than 359 goes back to 0 degee, then 1 degree etc..

    Only way to get 5 twists over a set distance is divide the distance into 5, twist that section and unite them into a single object.
    that seems to be the best bet

    thanks for your persistance to solve the problem
    Quote by George (AWDC Malta President) about Land Rovers:
    "Trid ittiha xebgħa mazza ta' bla raġuni"
    Translation: You have to attack it with a mallet for no reason at all"

  9. #9
    Super Moderator fuccaro's Avatar
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    Default

    Just a word of nostalgia: up to AutoCAd 2006 this was the way to twist bars:
    http://www.cadtutor.net/forum/showthread.php?t=221
    The Loft and Sweep commands are *so* sweet, isn't it?
    It's nice to be nice, but sometimes is nicer to be evil!.
    Tip: Please do not PM or email me with CAD questions - use the forums, you'll get an answer sooner.

  10. #10
    Junior Member wh33lz's Avatar
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    Default

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    Thanks mate, I had to get it right for a drawing I was doing for a client and it was the only element I was stuck on, and the clock was ticking.
    Thanks to this fantastic forum, and it's members, for alwyas steering someone in the right direction.


    Wow! thats some serious problem solving right there Fuccaro! Awesome effort.

    Indeed, Sweep and Loft are amazingly simpler!

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