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Tangent arcs flip directions
christoph_schmitz
Member Posts: 11 ✭✭
in General
Hi,
in one sketch I use a couple of arcs that flow into straight lines. Now an arc can be tangent to a line by continuing in the same direction (0 degrees), or go right back in the direction the line came from (180 degrees). In my model, some of the tangent arcs flip back and forth between the two depending on other geometry.
Is there a way to constrain the arc and the line in a way that prevents the 180 degree case? I'd rather have my sketch break than turn into some contorted shapes that are hard to move back. I have tried to add an angle constraintgeometry at the joint between the arc and the line, but that doesn't seem to work.
Thanks
Christoph
0
Best Answer

OptionsNeilCooke Moderator, Onshape Employees Posts: 5,514I just think it needs a little help  this seems to work:
1. Create 2 construction lines tangent to the ends of the other curves and dimension the length equal to your tangency value:
2. Create a spline coincident with the start of those curves and snap the spline tangency handles to the ends of those curves:
Senior Director, Technical Services, EMEAI6
Answers
I think in part I was just being stupid :), see below.
Here's a document that illustrates what I observed:
https://cad.onshape.com/documents/f4fc462cbce27d8bfdbc5d95/w/089a8c7db69016406335e7b5/e/8046bbfbfe9d50ebd24f9401
... in the Misc/Tangent Problems part studio. I was trying to create a boomerang shape from six arcs and two straight lines by first drawing the shapes (Sketch 1), then connecting those with coincident constraints (Sketch 2), then adding tangent constraints (Sketch 3 is what I want). Sketch 3a is what I sometimes end up with when the tangent constraints being added on the arcs throw things around quite a bit and then I try to drag all the arcs and lines into their approximate places before dimensioning them and tying them down, so to speak.
The problem, I guess, is that I should not try to add the tangent constraints last and wait for things to fly all over the place.
Christoph
1. Create 2 construction lines tangent to the ends of the other curves and dimension the length equal to your tangency value:
2. Create a spline coincident with the start of those curves and snap the spline tangency handles to the ends of those curves: