topic Re: Extrusion flips for no reason? in Fusion Support Forum

Extrusion flips for no reason?

chrisCFHNJ — Thu, 30 Jun 2022 20:11:07 GMT

Here is an example of probably the number one problem we have with fusion right now: Extrusions (or sketches) unexpectedly flipping.

https://screencast-o-matic.com/watch/c31vFKV0qFR

https://a360.co/3Ai7RBY

Any way to prevent this? What can be done?

My goal is to create a lot of parametric subassemblies for use in all sorts of custom ways. If we had the stability, Fusion 360's potential is really amazing. But we can't get there without improved stability.

Betreff: Extrusion flips for no reason?

g-andresen — Thu, 30 Jun 2022 20:10:05 GMT

Hi,

please share a file for investigation

günther

Betreff: Extrusion flips for no reason?

chrisCFHNJ — Thu, 30 Jun 2022 20:11:25 GMT

oh, sorry I forgot. I added it.

https://a360.co/3Ai7RBY

Betreff: Extrusion flips for no reason?

davebYYPCU — Thu, 30 Jun 2022 21:23:42 GMT

What can be done?

First words in your video, were 3d sketch,

then first thing you show us is that sketch that is not fully defined,

Asking parameter changing to be stable in either type of sketch is unreliable to say the least.

Might help....

Betreff: Extrusion flips for no reason?

chrisCFHNJ — Thu, 30 Jun 2022 21:32:22 GMT

1. The 3D sketch is fully defined.
2. The problem I am pointing out is that the extrusion flips directions. This should not be affected by the sketch. Even if the sketch changed sizes, the direction of the extrusion should stay consistent.

Betreff: Extrusion flips for no reason?

TrippyLighting — Thu, 30 Jun 2022 21:44:09 GMT

@davebYYPCU wrote:

What can be done?

First words in your video, were 3d sketch,

then first thing you show us is that sketch that is not fully defined,

Asking parameter changing to be stable in either type of sketch is unreliable to say the least.

Might help....

Before commenting on a screencast it might help to take a look at the assembly, scroll through the timeline and see how it behaves.

This issue is the same or very similar as the OP posted in this thread.

Heck even if I apply a rigid group to the Kick STD 1 Sleeper v5 assembly, before patterning some the rigid group stuff "jumps" around. There is a serious bug at play here!

Betreff: Extrusion flips for no reason?

davebYYPCU — Fri, 01 Jul 2022 01:29:38 GMT

I don't profess to know how 3d sketches work, fully constrained but not black, still learning.

Working with this file, is another good reason to avoid them.

I moved the timeline Marker before the timeline group, and even then,

Changing the witdh parameter corrupted the file result. 2 sketches and 3 components, weird results, so nothing after that timeline marker is in play yet. Second sketch is 2d and fully defined, did not contribute to the error as I see it.

So I figure the same culprit is at play in the other thread. (Similar to Redefine sketch Plane result IMO.)

I can trust 2d sketches. See if this one breaks.

Might help.....

Re: Extrusion flips for no reason?

jeff_strater — Fri, 01 Jul 2022 02:21:01 GMT

Extrude direction for 3D sketches is inherently unstable. For a 2D sketch, the extrude direction can be tied to the sketch normal, but for 3D, we have to rely on computing the direction based on the profile itself (using cross products, etc). That can be unstable under edit. For that reason, it is best to stick to 2D sketches whenever possible, and use 3D sketches for things like sweep paths, loft guide rails, etc. Alternatively, if you really want to use 3D sketches, you can define your own direction using Sweep, but you lose a lot of functionality that is available in Extrude.

Re: Extrusion flips for no reason?

chrisCFHNJ — Fri, 01 Jul 2022 13:38:11 GMT

ok, this is good to know. Typically I don't extrude from the 3D sketch itself, but I did in this case.

One more question for you though. Should I completely eliminate the 3D sketch from my assembly template, or just avoid extruding directly off of it? I have planes created that align with the sketch on each side. Is it ok to create a new sketch on those, and then relate the 2d sketch to the 3d sketch? I could remake my template and use several 2d sketches instead of the 3d sketch if that would be more stable.

Re: Extrusion flips for no reason?

TrippyLighting — Fri, 01 Jul 2022 16:27:45 GMT

I am going to suggest something unusual, but it is incredibly stable and efficient.

There is not doubt about which way the normals point either.

Instead of creating a base sketch and then multiple individual sketches that basically define the sides of a box, why not just create an extrusion, a solid body with 6 sides that you can create further sketches on if/when needed.

I personally welcome any opportunity to simplify or even avoid sketches ... in any CAD application.

You can always remove the body at the end of the timeline if you don't want additional stuff in a BOM.

See how short that timeline is.

Re: Extrusion flips for no reason?

chrisCFHNJ — Fri, 01 Jul 2022 16:29:33 GMT

That does make a lot of sense. I will try it. Thanks!