Sweep fails after changing underlying reference coil angle; ctrl-B sometimes fixes it, but causes lost body error on dependent operations (REPOST)

[cdelguercio]

Repost of:

https://forums.autodesk.com/t5/fusion-360-support/sweep-fails-after-changing-underlying-reference-co...

I have a Sweep that follows a Path + Guide Rail that in turn come from a reference triangle Coil. The profile for the Sweep is constrained to the bottom end of the Path helix. The reference triangle Coil is defined by a User Parameter for the pitch, which is defined as "2 * pi * inner_radius * tan(theta)" where "theta" is another User Parameter in degrees. In the provided .f3d if I change theta from 1.1 to 1.2 and back again, the Sweep operation will fail. Ctrl-B will sometimes fix it, but since a New Body is made with a different name (BodyX), this causes the simple Cut operation that I do next to fail and give a "the target body is lost" error.

My two questions are:

1) What is causing the sweep to fail for certain values of theta; it doesn't seems like the coil geometry is interfering with itself, even at these tiny angles.

2) Is there a way to force the Sweep to not make a New Body that clobbers all future references to the Sweep object?

In the previous post jeff.strater found that one of the issues was that the Path Distance and Rail Guide Distance were being set to zero after changing a user parameter. In addition to that problem, after I manually set the values to 1, the model fails again with the cut at the end, where it complains that the "target body is lost".

[HughesTooling]

A couple of things to note.

One, don't use project to make a copy of the edge of the coil, the sketch spline is not as accurate as the model edge, so use the model edge. 

Two. You'll get better results if the profile is perpendicular to the helix rather than parallel with the axis. One big problem with the coil feature is it squashes the profile the more steep the helix angle.

Attached is a modified version or you design using a sketch plane parallel to the helix and a twist angle rather than the helix as a path. Had to caculate the twist angle off the height you had set to 75.467 mm.

[HughesTooling]

Here's another version that does away with the coil primitive, big problem with Fusion's primitives is they are not fully paramedic and you can't fix and edit their position. 

In this version I use sketches and a surface sweep to create a helical surface. Only need this to set up the plane for the sweep profile. I just realised I could just use your theta to set up a plane at angle🙄. I'll create another version in a minute!

[HughesTooling · Accepted solution]

OK, this is the simplest version using the least features. Seem to be robust and doesn't break when changing theta.

[cdelguercio]

Wow thanks a lot for your solutions Mark. I think I copied my original method from somewhere else on the forum, but your answer seems a lot more robust.