Problems fully constraining drawing

[rickduley]

This is the base sketch of a textbook exercise.

The drawing is turned blue, which usually indicates that it is fully constrained. Yet ...

1.  Why do I still have the two Degrees of Freedom?

2.  Why does Inventor tell me "2 dimensions needed"?

3.  How do I specify that the top horizontal line is centred?

All assistance appreciated.

[nmunro]

The DOF symbols (the red arrows) are the answer to your questions. The two endpoints of the construction line are free to move in a vertical direction. You can use geometric constraints to limit their movement (end point coincident to the nearest hor line or midpoint of said line), or dimensions to 'fix' their location.

Neil

[rickduley]

Thanks, Neil, but the bottom left corner is constrained to the Origin.  That should fix the bottom horizontal line, and the 67mm dimension should constrain the vertical movement of the top horizontal line.

Shouldn't that solve that issue?

I forgot to attach the sketch.  Here it is.

[rickduley]

Can someone please deal with the third question ...

"3.  How do I specify that the top horizontal line is centred?"

Thanks

[nmunro · Accepted solution]

Please re-read my first reply, it is the construction line that is underconstrained (the vertical dash-dot line up the middle of the sketch). The red arrows are DOF indicators for the end points of this line. Your other geometry is defined. By fixing the underconstrained construction line you can easily force the upper line to be centered on the part; the construction line is constrained to the midpoint.

The attached revision shows a fix, plus I removed the coincident constraint between the part origin and the lower left point, and replaced it with one coincident to the midpoint of the lower horizontal line. Use symmetry (if practical) whenever possible. You may have reason to constrain to the lower-left corner (i.e. Datums) so ignore that change if it does not suit your purposes.

Neil

[rickduley]

Sorry I missed that.

Thanks Neil