Autodesk Inventor

[#1]

I've created associative 3D sketches to use as trajectories for sweeps.  I will often have to use one line extending from the end of another line.  I make the two lines colinear.  But when the model changes, sometimes one line will change direction and cause an overlapping condition which makes the sweep fail.

Has anyone experienced this and found a way to keep it from happening?  Ideally, I'd create one line that extended, but you can't constrain a line to a point, only an endpoint to a point.

I'm attaching the model.  Hopefully that will help to make the situation clearer.

[#2]

Bill,

Could you show me how to the see the line flipping behavior with the part you attached?

Thanks!

[#3]

I captured a video of "breaking" the 3D sketch, the resulting error and then fixing the 3D sketch.  Usually, the 3D sketch gets broken when changes are made in the parent assembly.  Link below.

Video Capture

or

http://www.screencast.com/t/ZdDanmbuxpRl

[#4]

Bill,

Thanks for recording the video to show the behavior! The issue here is that from sketch solver's perspective, the closest mathematically correct solution in this case is to flip, as opposed to the original direction. Unfortunately, it is opposite to your intent.

Is there any reason why the colinear constraint has to be placed last? Could that segment be grounded without violating further update?

Thanks!

[#5]

If the segment were grounded and the parent assembly to which it is associated changed, wouldn't that prevent the 3D sketch from following it?  The sweeps represent flexible conduit and they need to be able to follow the components they are attached to, in the event that those components move.

Is there a better way to constrain the line segments to completely nail down the direction?  Ideally, a single line segment could be used instead of two where X represents a point and - represents the line, it would look like this:

X-------------------X----------------

The first X would be constrained to the end point of the line while the second point would be constrained to the line itself, not the endpoint.  I don't know if you could reverse the direction of the line and still meet the constraint conditions or not.

[#6 · Accepted solution]

When this happens to me, I try to find a way to dimension both ends of the line segment from an origin (or work) plane.  This makes sure that the line doesn't flip directions.  For example, the image below shows one such segment.  The two indicated dimensions are for each end of a line segment (that has a bend applied to it).  In this case, the dimension on the left is just the parameter of the dimension on the right, minus 1.

This example is from the attached part, 3D Sketch6.

[#7]

I'm not sure how I could do that in this application.  One end is attached to a point.  Only the one end is free to be dimensioned.  I've tried dimensioning it from a point instead of just dimensioning its length, but that didn't appear to help.

[#8]

I forgot to mention that I have Inventor 2012, so I can't open your part to see exactly what you are trying to do and whether or not my suggestion is even applicable.

Sorry to hear that it won't work for you.

If I may, I suggest that in the future you post some screen images (in addition to the Inventor files) so that other users who are on previous versions can better understand your question.

[#9]

I tried to attach a capture showing where this is used.  The green-circled areas are where I tend to have the problem.  Both ends of the segments with reference dimensions on them are constrained to mating geometry.  The segments extending from the reference-dimensioned segments with the dimensions on them are the ones that flip.  Hope that helps.

[#10]

Was this tube created in place (i.e. was the new part created in the context of the assembly)?  If it was, it is likely an adaptive part with cross-part references.  In this case, it is possible to create work planes at the beginning and end points of your tube.  These work planes would be constrained to the fittings and you could use them to help constrain your line endpoints so that they don't flip.

Edit:  My bad.  You posted a link to a screen-capture video.  I am blind and didn't notice it.  Try the work plane thing.  I think it will work.