topic Scissor Jaw over-constrained in Fusion Design, Validate & Document Forum

Scissor Jaw over-constrained

Anonymous — Mon, 28 Aug 2017 05:28:41 GMT

Hi, I am doing the Sketch problem Modifying Sketches 1. the scissor jaw. The problem I am having is that I apply the dimensions and Fusion 360 says that it is over constraining the sketch by doing that. I do it anyway and when I am finished and try to move the edge of the scissors the spline moves away from its points. Could someone explain what is going wrong and how to do it right? Please see the attached Screencast.

Re: Scissor Jaw over-constrained

Brady_Fulton — Mon, 28 Aug 2017 14:17:41 GMT

Do you only want the lower jaw to move?

Instead of forcing the dimensions, you could also "Fix" the points and segments. Select the sketch objects you want to affect, then click "Fix/Unfix" in the sketch palette under the Constraints heading.

You might also think about just sketching and extruding one of the jaws, then using a body (can't joint bodies) or component mirror you can then add a joint to simulate the motion.

Re: Scissor Jaw over-constrained

jeff_strater — Mon, 28 Aug 2017 15:21:25 GMT

Hi @Anonymous,

Everything that @Brady_Fulton says is correct. I also noticed from your video that you are probably not editing the correct sketch. I see that you have 3 sketches in your timeline, and I suspect that you really only want one:

This is also why, when you are dimensioning the sketch, you get the purple (projected) points. These points have been auto-projected into the active sketch from one of the earlier sketches. They are fixed points (because they are driven from the earlier sketch points), which is also why you get the over-constrained warning:

and also why, when you try to drag the sketch, it separates from the purple points:

When you drag, you are dragging the earlier sketch, and the later sketch (which has the projected points) won't update until you finish the drag.

So, I suspect the missing step was editing an existing sketch, instead of creating a new one. Select the sketch in the timeline, right click, and choose "edit sketch" to get you back into that sketch.

Jeff

Re: Scissor Jaw over-constrained

SaeedHamza — Mon, 28 Aug 2017 15:26:04 GMT

Hi,

Could you attach the file so that we can try

because some constraints can differ between points+points and points+lines

Regards

Re: Scissor Jaw over-constrained

Anonymous — Tue, 29 Aug 2017 01:07:41 GMT

Thank you. I tried @jeff_strater solution and it worked perfectly. Thanks also to @Brady_Fulton.