Overconstrained sketch

[Anonymous]

Hi, I'm a total noob at fusion 360, trying to practice learning but for some reason I get this error message saying that the "sketch is overconstrained" please help as I'm not able to use the dimension feature as it doesn't let me toggle to driving and gives me driven dimension.

[dsouzasujay]

Hi @Anonymous ,

From the image its not clear which sketch you are constraining.

Can you attach this design by File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

Edited:

If you are constraining a purple colour sketch then its a projected sketch and you cant constrain it.

If you want to constrain a Purple sketch then you need to first break link(Right click on the sketch and select break link)

[Anonymous]

Hi sure, of course, thanks for your response, I am attaching the file below so please have a look.

[Anonymous]

Sorry but I don't want to want to use dimension on the purple lines but the two white vertical lines where you can see the driven dimension of 15.3, I just want to make it as driving dimension with 14mm between both the lines. 

Please help <_<

[dsouzasujay · Accepted solution]

@Anonymous 

The sketch is already constrained.

If you can see below image, by hiding the body/bodies from the browser then the sketch will be clearly visible.

The Vertical line is constrained by Coinciding one of its point to the projected sketch(Purple one), if you can delete it then you can add Sketch dimensions.

[PinRudolf · Accepted solution]

Hi Mohammed,

Notice the white line at the right hand side is attached to the purple line at the bottom. The ends of those two lines attach, Fusion understands that you want to keep those attached. We call that attachment a constraint. 

The idea of this constraint is that if you would move the right side line, the bottom line would need to get longer or shorter. Point to point constraint is called a Coincident constraint.

The purple line is a projected line. That functions like a copy, but is constrained to the original line as well. So when the original line gets longer, the Projected line will get longer. This doesn't work the other way round though, the purple line will stay the same length as long as that original line does not change. Hence the reason you can't change that dimension.

What you probably want to do is break the constraint between the two lines. Click the line on the right. A little icon should appear just at the attached point indication there is a Coincident constraint:

Right click this icon and select Delete. The constraint is now removed. 

Remove the dimension as well and place it again. Note how this is now a normal constraint and you should be able to change the dimension.

As a side notes: 

• The Coincident constraint is placed because you drew it to the end of an existing line. When you would have drawn it next to the end, so the ends don't touch, the constraint would not have been created. 
• Holding the CTRL-key prevents constraints to be created automatically
• Right clicking a Driven Dimension gives you the option to 'Toggle Driving'