Tangent Point Construction

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  • Tangent Point Construction

    I have need to construct a tangent point of circle and line. I don't see a way to do this in PC DMIS (3.73 CAD). Any ideas?
    Bill Jarrells
    A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

  • #2
    construct a point by piercing the circle with the line, if the point shows way off in space reverse the vector of the line construct a new pierce point.
    Kevin

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    • #3
      You will only get a pierce point IF the line intersects the circle. First of all, where is this line coming from? CMM's are not prefect, the only time you will find a line exactly tangent to a circle is in a cad package. You MIGHT get lucky and have one once in a while as measured features on a CMM, but you will more likely get one that intersects the circle in 2 places or not at all. You might have to construct a line perpendicular to your line, going through the center of the circle, then do a pierce of the constrcut line and the circle. If it grabs the wrong one, construct yet another line, but this time create the reverse of the perp. line (it is an option).
      sigpic
      Originally posted by AndersI
      I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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      • #4
        No CAD, but it is a Radius blend into a flat. I understand the imperfections involved but want a 'closest point of approach' type feature. I am using pierce point currently. I do a 3 hit radius with the last hit as close to the intersection as I care to go. Then the first point of the line is as close to the other side of the intersection as I want to go. I get a value, but since it didn't construct as a tangent point then I don't know how true it is. Variation, overlap etc. Too far away from the intersection and it won't pierce regularly. Too close and overlap. At least that is the impression I get from it.
        Bill Jarrells
        A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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        • #5
          Yeah, sounds like you need to do the perp-line and pierce. Adding more points to that radius wouldn't hurt, either, with the perp-line/pierce.
          sigpic
          Originally posted by AndersI
          I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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          • #6
            Got you. I have to tread on shakey ground there. Narrow anlge radius. Inherently distrust the center. Oh well, I will experiment with that.
            Thanks everyone.
            BTW, does CAD ++ Allow tangent intersections?
            Bill Jarrells
            A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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            • #7
              We might be able to help more if you could post a drawing or sketch.

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              • #8
                Originally posted by Goodluck View Post
                We might be able to help more if you could post a drawing or sketch.
                I can certainly do a sketch. Not sure I know how to post it. I will try to figure that out.
                Thanks.
                Bill Jarrells
                A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                • #9
                  Try a cast point.

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                  • #10
                    Originally posted by Wingman View Post
                    Got you. I have to tread on shakey ground there. Narrow anlge radius. Inherently distrust the center. Oh well, I will experiment with that.
                    Thanks everyone.
                    BTW, does CAD ++ Allow tangent intersections?
                    NOPE.

                    However, if you are worried about getting good hits due to variability, measure it twice, this way:
                    1) Measure the line on each side of the radius (WITH cad data), one of which will be your 'tangent' line
                    2) Construct the intersection point of the 2 lines
                    3) Program the radius using Autofeature Circle, RELATIVE MEASUREMENT to that intersection point AND turn on the RE-MEASURE function.

                    What this will do, as long as you have correct XYZ noms for all the points/features is it will measure the radius the first time in correct cad relationship to the intersection point of the 2 lines (no matter WHERE they ended up being in space) and the re-measure will then measure the radius again, using the actuals from the first measurement as the target point for the second measurement.

                    As for adding more points to the radius, if you are only using 3, the roundness of the radius will always be perfect and the roundness value, even if you don't need it for the report, will give you a good idea IF you have good hits. 4 or more hits are needed for this.
                    sigpic
                    Originally posted by AndersI
                    I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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                    • #11
                      Originally posted by Wingman View Post
                      I can certainly do a sketch. Not sure I know how to post it. I will try to figure that out.
                      Thanks.
                      I always just try to put something together in paint real quick. Then, if you have a recent enough version of paint, you can save it as a jpg and post that.

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                      • #12
                        I did a sketch in Excel before I read this. Can I post that? I see a button for an image but noting for a file.
                        Bill Jarrells
                        A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                        • #13
                          Here it is

                          Did this work?
                          Bill Jarrells
                          A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                          • #14
                            I did the paint thing and hope it is attached correctly.
                            Last edited by Wingman; 08-29-2007, 08:07 PM.
                            Bill Jarrells
                            A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                            • #15
                              Matt has the correct solution for your issue. I have used the perp line thing before with suprising success.
                              sigpic GDTPS - 0584

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