Constrain commands fails

[Parmegianisp]

Hello dear,

My problem always starts when I need to use Constrain commands: Parallel, symmetric, perpendicular.

If I have two lines, both vertically. Left side line A and right side line B. And I want to make line A parallel to line B, but I also want to make line B parallel to line A.

Then I apply the parallel constraint command. 

First I click on line B and then on line A, it will make line A move parallel to line B.

However, if I first click on line A and then line B, it would be correct for B to move parallel to line A. But what happens is that line A will move again, and line B will become still.

For the other commands it happens the same way. In the Symmetric command, only the left side of the picture will be symmetrical to the right. If I want to make the right side symmetrical to the left, It will not work and I will have to use the Fix command to do this.

I will be very grateful if someone can help me.

Daniel.

[SBix26]

A little experimentation in Inventor 2020 seems to indicate that the line that was placed first remains still and the more recently placed line changes angle, regardless of selection order.

But it seems that you are not understanding how sketch constraints work.  The parallel constraint make the two lines parallel to each other.  Period.  If there are no other constraints, you can move either one of them, and the other moves, too, to remain parallel.  If you have constrained one of them to some angle vs. the origin axes, then it will remain at that angle, and the other line will, too.

A sketch with two unconstrained lines has eight degrees of freedom.  Adding a parallel constraint as you describe removes one of those degrees of freedom, leaving seven.  You will need more constraints and some dimensions to remove those seven DOF.

Perhaps you could post a file, an image, or a Screencast video of your situation and describe what you're trying to accomplish.

---

Sam B
Inventor Pro 2020.1 | Windows 7 SP1
LinkedIn

[johnsonshiue]

Hi Daniel,

Constraint solving is usually bi-directional. It depends on the existing dimensions/constraints, the movement, and some assumptions made by the solver. If you see unintuitive behavior, please share the file here so forum experts can take a look. There should be a logical explanation.

Many thanks!

[Yashasvi23481]

Hi Daniel,

  You need to constrain/define first line completely before applying any constrain to it. Try adding angle to line A  and give dimensions to it. Once you fix them by dimension and constraint, you don't need to use lock/fix feature.  If both are variable, you cant control their movement as Degree of freedom is floating for both. 

So in nutshell, pre define 1 of the lines A or B fully i.e., reduce degree of freedom before applying any relation to it. 

Hope that helps.

Regards,

Yash