Finding location of tangent point

[mgnt8]

Here's one that's baffled me for awhile. Say you have a circle and you sketch a line that isn't vertical or horizontal and make it tangent to the circle. The line doesn't begin or end on the circle. Can do you determine where the tangent point is exactly? It seems that Pro/E won't let you place a point that lies both on the line & the circle.

 

[anand_m_s]

Hi mgnt8,


The solution is pretty simple. Draw a line from the centre of the cirlce to the tangent line so that this new line perpendicular to the tangent line. The point of intersection of the two lines is the point of tangency between the circle and the tangent line.


Regards,


Anand

 

[mgnt8]

Thanks, that's weird that you can place the endpoint of the line on the first line and circle, but not a single point.

 

[Jacoolo]

You can analize this point by skecthing a line on the circle and then use in Sketch mode Analisys > Tangency point

 

[anand_m_s]

Hi Jacek,


This analysis feature does not give details about the point of tangency. Also, this point can not be located for further usage in geometry construction.


Hi mgnt8,


From Pro E point of view, the end point of the radial line does not lie on the circle. It is just a line starting from the centre of the circle and ending on the tangent line. But from the properties of circle we know that, on any point on the circle, the radial line and the tangent lines are always perpendicular to each other.


Regards,


Anand

 

[Jacoolo]

well, for me it does and if You want to have the point at tangency point You should proceed as following:

*make a sketch as below - first circle, then tangent line and at the end line from center of cirle to tangent line perpendiclar to it. The end point of last line is the tangency point

 

[mgnt8]

Thanks for the tip Jacek. I've never used sketcher tangency point analysis before. One more question - is there a way to make a line tangent to a spline not at the endpoints?

 

[Jacoolo]

haven`t found such Tip so far

that was a question I asked at Polish PTC conference this year while introduction of WF 5.0. The guy who leads the speech was not happy about that

 

[solidworm]

the suggested solution can be only applied to a circle and a line, if it's a spline, center of curvature should be used instead of center point. which can be found with some tricks.

the problems is that after sketching a circle and a tangent line, placing a point , adding coincident relation between the point and the line, it does not allow to add another coincident relation between the point and the circle.


Edited by: solidworm

 

[solidworm]

Thanks for the tip Jacek. I've never used sketcher tangency point analysis before. One more question - is there a way to make a line tangent to a spline not at the endpoints?

this is also frustrating, why ProE cant do that easily. if you convert the spline in another sketch (use edge), then by placing the first point of the line on the converted spline, it can build a tangent relation.

another mothod: add three points coincident with the spline (very close to each other, at the desired point). sketch a circle using three point method. the center of that circle is the center of curvature at that point. now, use the mothod which others suggest above.
(holy cr..! it cant make a point on the spline in one sketch!)

Edited by: solidworm

 

[mgnt8]

another mothod: add three points coincident with the spline (very close to each other, at the desired point). sketch a circle using three point method. the center of that circle is the center of curvature at that point. now, use the mothod which others suggest above.

SW, I'm not seeing how this works. Can you post a picture?

 

[solidworm]

it's an approximate method. in the picture above,there are 3 coincident points with the spline (spaced .0001 mm horizontally)
now if a circle is sketched passing through those points (circle using three point method), that circle is something significant.* because it's radius is the radius of curvature (=1/curvature) of the spline and it's center is the center of curvature (at that point of the spline).
and a line tangent to that circle at that point, will be tangent to the spline.

* it is called osculating circle in math.


Edited by: solidworm

 

[mgnt8]

it's an approximate method.
and a line tangent to that circle at that point, will be tangent to the spline.

* it is called osculating circle in math.

Yor the man, dude- that works splendidly. I wish I would have known about this method a long time ago. Might have saved me a lot of time. It looks like PTC really has some room to improve the spline feature in sketcher. There's a lot more they could be doing with it. If they could just combine sketch splines & ISDX curves, they'd have something dangerous.

 

[solidworm]

I'm glad you found it useful.