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CAD geometry question

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  • 20-08-2012 2:26pm
    #1
    breadmonkey
    Registered Users Posts: 3,608 ✭✭✭


    Folks,

    I need to draw a line of fixed length from a fixed point on a horizontal line to the tangent of a circle. Anyone know if I can do this in CAD?

    [IMG][/img]cadl.jpg


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    #2
    CatFromHue
    Moderators, Science, Health & Environment Moderators Posts: 18,140 Mod ✭✭✭✭CatFromHue


    What program are you using?


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    #3
    CatFromHue
    Moderators, Science, Health & Environment Moderators Posts: 18,140 Mod ✭✭✭✭CatFromHue


    swsketch.png


    On the left half the line does not have a tangent constraint to the circle so you can put in the length of the line.

    On the right half the line does have a tangent constraint to the circle so can't put in a length for the line.

    This is on Solidworks


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    #4
    chris85
    Registered Users Posts: 4,502 ✭✭✭chris85


    I think you need to remove the constraint from the centre of the circle to the end of the line, or remove the constraint from the end of the line to the horizontal axis of the circle. With both of these in place you will not be able to get a tangent and fixed length as no freedom of the point at end of line to move.

    If one of these is removed than you should be able to tangent and get a fixed length on it. Thats how I see it anyways.


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    #5
    Turbulent Bill
    Registered Users Posts: 1,622 ✭✭✭Turbulent Bill


    breadmonkey wrote: »
    Folks,

    I need to draw a line of fixed length from a fixed point on a horizontal line to the tangent of a circle. Anyone know if I can do this in CAD?

    It's not possible exactly as you've drawn it, as the centre of the circle is at the origin. If both points "a" and "b" of the line are fixed (defining both the line length and its position), then the circle centre and radius can't be constrained if the line is to be tangent. Similarly, if only "a" and the line length are fixed (i.e., line free to rotate around "a"), then the circle centre can be on the origin with just its radius unconstrained.

    Note that this is a fundamental geometric restraint, not a CAD one. Any CAD program worth its salt will flag errors if you try to over-constrain geometry.


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