Construction a Circle

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  • Construction a Circle

    When 'Constructing' a Circle, what is the difference between "Projection" and "Intersect"?

    Usually, my true position to an angle hole (which is drilled into the side of a bore) is called out to where the hole intersects the plane of the bore. I measure the plane. rotate my alignment to the nominal hole angle, Auto Circle the hole, project the circle to the plane, rotate my alingnment back, then report the true position of the hole. Has always worked in the past.

    Today, I have a similar situation but 'Projecting' to the plane gives me an incorrect true position (approx .020" off). Though when I 'Intersect' the hole to the plane instead of 'Projecting it', the true position is good.

    This is the first time I have ever 'Intersected' an angle hole to a plane.

    Which way is correct, what is the difference and must I go and fix all my previous programs?

    Thanks again gurus. I long to be a guru someday.
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  • #2
    Originally posted by Big Red View Post
    When 'Constructing' a Circle, what is the difference between "Projection" and "Intersect"?

    Usually, my true position to an angle hole (which is drilled into the side of a bore) is called out to where the hole intersects the plane of the bore. I measure the plane. rotate my alignment to the nominal hole angle, Auto Circle the hole, project the circle to the plane, rotate my alingnment back, then report the true position of the hole. Has always worked in the past.

    Today, I have a similar situation but 'Projecting' to the plane gives me an incorrect true position (approx .020" off). Though when I 'Intersect' the hole to the plane instead of 'Projecting it', the true position is good.

    This is the first time I have ever 'Intersected' an angle hole to a plane.

    Which way is correct, what is the difference and must I go and fix all my previous programs?

    Thanks again gurus. I long to be a guru someday.
    The plane of the bore??? Do you mean the plane around the bore?

    I would measure the bore as a cylinder and the angle hole as a cylinder and intersect the two. (If possible). If you can only measure the angle hole as a circle you might be able to project to the cylinder if you are aligned to the cylinder and rotate the alignment as you describe above.

    To answer your question about projection vs intersect. Projection is a 2D "translation" of a point "up" to a plane. Intersection is an actual 3D point where one feature intersects another, (or the centerline or one or both features intersects the other).

    Another construction that is often useful is "pierce" if a line pierces a cylinder you get the location on the diameter of the cylinder, (instead of the centerline). Which side of the cylinder is dependent upon the vectors of your features and the order of selection. These are somewhat simplistic explanations, but should get you going in the correct direction. The help menus (F1) have more details about how these constructions work. HTH
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