Trimming offset arcs (ellipses) bug

[etfrench]

The initial sketch items were created by projecting imported components from another Fusion 360 project. New offset arcs were created from the projected arcs.  Trim operation failed in one of the four operations:

The purpose of the offset arcs is to create a boundary for a CAM operation.  I can work around the bug by creating new arc segments using the Center Arc tool.

p.s. These are actually ellipse segments, not arcs.

[HughesTooling]

One thing to be aware of is when you offset an ellipse you get a spline not an ellipse, if you draw 2 ellipses using the same centre point you'll see why. What I noticed is you've drawn lines to close the gaps on all but one of the offsets, on one you've moved\extended the spline,  it probable still shouldn't fail but it may have twisted the spline so it's not planar any more. Here's a screencast that show it works fine if I delete the modified spline and redo the offset.

Mark

[HughesTooling]

I just tested using extend and that works so I'm not sure what you did differently on that one offset that causes the problem.

Mark

[etfrench]

I don't know what's different between the two upper sets that would cause the trim failure.  They were created in the same manner, but the upper left offset spline appears to be different as it doesn't have the co-incident markers. The trim operation finds one crossing, but not the other.

[Beyondforce]

You could try to use the Break tool in the area that you want to cut. That should solve your problem.

Ben.

[etfrench]

The break tool has the same problem.  It's only seeing one crossing.

[Beyondforce]

Please attach the file, so we can test it.

[etfrench]

The attached file is in the first post.

[Beyondforce]

Here you go, I hope it helps:

Cheers / Ben
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[etfrench]

I'm not having any problem doing a workaround for the trim bug.  The trim command had no problem with the splines in the upper right, but failed on the splines in the upper left.  The lower sets were trimmed by creating new crossing points with lines.  The same method will work for the upper left splines.

The break command almost worked.  It found the uppermost crossing point on the left.  Once that command was completed the break command found the lower crossing point.  The trim command was able to remove the center segments, but left the sketch in an unusable state as you can see by the all white background. 

The purpose of this sketch is to create a boundary for a CNC pocket operation where the tool will completely clean off the material above the ellipse.  To do this it has to have the centerline of the tool run on the ellipse boundary. On the straight sides of the component the tool has to stay inside of the boundary. There isn't any requirement for super precision. Here's what the tool paths look like:

This sketch is only showing a small portion of the parts to be machined so it isn't centered. 

Fusion 360 can't do nesting for CNC automatically yet.  It's a bit tedious to set the individual components in the correct position to be machined, especially when the raw material is just large enough to hold the parts.

[Beyondforce]

3 things:
1. When you have symmetry in your sketch like yours, use Mirror. It will save you time.
2. Why the right side don't work like the left side, I really don't know. Maybe @jeff_strater has an explanation.
2. In regards to CNC, @PhilProcarioJr is the guy you should talk to.