Angle Constraint (Rotation Direction)

[Mike Allen]

I'm probably just missing something here, but when I apply an angle constraint between two shapes (one is a hole shape, with dimension constraints to keep it's center fixed on the other shape), I'm unable to predict which direction it will rotate when I change the angle. For instance, if I start with the constrained edges at 90 degrees & change the angle to 45 degrees - as often as not, it will rotate 135, or 225, or 315 degrees.

 

What I need is plus or minus 67.5 degrees from the 90 degree position.

 

Any ideas?

 

angle_constraint.7z

Edited December 9, 2009 by Mike Allen

[Mike Allen]

I'm giving this another try as a Structured Part. I need to constrain the center of the cut feature arc at a specific point from the end of the stock. Then I want to drive the angle of rotation through parameters.

 

In the position shown, it's easy enough to put Smart Dimension constraints for X & Y of the center of the cross section arc, then put an angular dimension between the straight edge of the cross section & the bottom edge of the stock. The problem arises when I try to change the angular dimension - all my dimensional constraints go away. Is there another way to make these constraints?

[Mike Allen]

OK - I think I'm getting very close here.

 

I'm using construction lines in the sketch to provide the position constraints. I can parametrically drive the angle using Design Variations, until I pass 90 degrees - so 22.5 is OK, 45 is OK 90 is OK - and 135 is OK, but it must break something, because after that point, I can no longer drive the angle through Design Variations.

 

*******************

 

Hold on - now it's working. I changed nothing, but after setting the angle to 135 through Design Variations, I went to edit the cross section - but did not change anything in the sketch or constraints, because it all looked right. So I went back to Design Variations & have no trouble going from 157.5 to 22.5, to 90, to 45, to 140, to 30, etc.

 

I'm still a bit concerned, since I have absolutely no idea why it started to work right.

 

On a side note, I would really appreciate a tutorial on the best way to constrain sketches on structured parts. This trial & error can be quite frustrating, since when the constraints get broken, undo doesn't always set things right & I find myself scrapping the feature so I can start again.

 

Oh yes - was there a reason why we can't use the TriBall to position the grid when creating features on structured parts? It would really come in handy, because I like my sketch to have a direct relationship to 0,0 on the grid.