topic Re: Discussing the "Redefine Sketch Plane" problem in Fusion Design, Validate & Document Forum

Discussing the "Redefine Sketch Plane" problem

r.moss — Tue, 30 Jun 2020 13:14:23 GMT

There seem to be a number of similar threads related to "redefining sketch planes": https://forums.autodesk.com/t5/fusion-360-design-validate/redefine-sketch-plane-preview-looks-fine-then-flip/td-p/7517354

https://forums.autodesk.com/t5/fusion-360-design-validate/quot-redefine-sketch-plane-quot-breaks-projection-is-there-an/m-p/9558642,

https://forums.autodesk.com/t5/fusion-360-design-validate/redefine-sketch-plane-sketch-rotated/m-p/7840820 and

https://forums.autodesk.com/t5/fusion-360-design-validate/constuction-plane-normals/m-p/6434654.

I have just had the oft-repeated problem that redefining a sketch plane flipped my sketch upside down and lost its projections. Somewhat miffed, I played around a bit to figure out why it sometimes does this - see screencasts below. Judging from the response to the above posts, it seems AutoDesk might fix this annoyance at some point, so in this post I'm exploring the nature of the problem and what I would like to see in an improved version (before they do it and it's too late to make suggestions).

It seems that there are two kinds of sketch and you have no way of telling which you have (unless you can think back and remember how you created it):

Sketch on a face
Sketch on a construction plane

I found myself with two sketches apparently on the same plane but actually one was on a face. I had drawn Sketch 1 on a construction plane, extruded from that sketch, then created Sketch 2 on the end of the extrusion. I then decided that I would like Sketch 2 to lie on the body mid-plane so I rolled back the timeline, made a plane there and redefined Sketch 2 as being on that plane. Whoops! The sketch rotated 180 degrees about its x-axis (actually it does this if you click on a face that is solid in the +z direction but not if you use one that is solid in the -z direction, I'll come on to that).

Generally, F360 will try to do something sensible if relocating a sketch from one face to a similar face.

The problem arises if switching from a face-reference to a plane-reference, or between faces (or planes) with dissimilar definitions such that F360 does not find an obvious transformation to pick. Your sketch then rotates 90 or 180 degrees (about an axis either in the plane or perpendicular to it) and it can be half-impossible to reposition it as required using the Move tool.

Let's think for a moment about the kinds of redefinition that might be useful:

You have a body with several similar faces (cube, pyramid etc). You start with a couple of sketches on face 1, then decide that one should really be on face 2.
Ditto but your faces are dissimilar e.g. your "cube" tapers as seen from the x-direction but not the z-direction.
You have a sketch on a face, then decide you want that sketch to be on a plane coincident with the face (perhaps because the face is about to be deleted)
You want to switch from one of the xyz origin faces to an offset, angled or other custom plane

Looking at each of these:

(a), Fusion will probably redefine the sketch so it looks just like before as it sits on its face. Fine. If however you wanted to reflect it in the face1/face 2 joint line (perhaps a 3D sketch) so it was symmetrical with the original, I don't think you can do that. I don't think there's any other way of doing this either, so building it into "Redefine plane" would be a good way of providing a reflection capability.

(b) For this you would want to redefine the sketch origin (as suggested in the posts mentioned above). This could be done by the Move command, if it was tweaked slightly. To cover all possible eventualities you would want to define:

a sketch point and a target point,
a sketch line and a target line to which it should be parallel
whether to flip the sketch line direction (rotate 180 deg, in-plane), or
whether to reflect the sketch about a plane perpendicular to your target line, through your sketch point,
pick a plane-normal direction (flips the sketch above or below the target line) and
whether to reflect 3D components in/out of plane or preserve the original sense.

(c) If the new plane is coincident with the face plane, the sketch should not move (but as Galileo may have said "And yet it moves!").

(d.1) For offset planes the sketch should translate parallel to the plane normal. If this isn't what's wanted, the options under (b) above should sort it out.

(d.2) For inclined planes there are 4 geometrically-simple options that could map a sketch on plane 1 onto a sketch on plane 2, bearing in mind that the planes will intersect along a line "L" and that there will be both an acute and an obtuse angle between the plane normals:

Reflect the sketch in the acute-angle bisecting mid-plane between plane 1 and plane 2
Reflect the sketch in the obtuse-angle bisecting mid-plane between plane 1 and plane 2
Rotate the sketch about L though the acute angle
Rotate the sketch about L through the obtuse angle.

There are also variants that would position the sketch in one direction but give the user some choice in the second direction:

Specify a radius of curvature (user choice) and define an "acute angle" axis of rotation such that plane 1 rolls onto plane 2 about this axis, carrying the sketch with it.
Ditto, obtuse angle.

Basically these are the same as (iii), (iv) plus a user translation perpendicular to L.

The trouble with Redefine Sketch Plane at the moment is that it does not give you any of these choices. It would be good to have them "at the touch of a button" and pick the one you want.

To demonstrate the current behaviour I've done 3 screencasts. I think I can only insert one per message so I'll post a couple of "replies" with the others.

The first screencast (sorry, no sound) is with parallel planes and explores the difference between face- and plane-based sketches.

Screencast 1 (file "sketch redefinition v0").

I started by making four identical 2D sketches, differing only in that they sit on different planes:

x-y plane from the front "Front of xy sketch"
x-y plane from the back "Rear of xy sketch"
Front face of an extrude from 0 to -z "Sketch facing -z"
Back face of an extrude from 0 to +z "Sketch facing +z"

All these planes are coplanar (first 7 minutes of screencast).

I then selected the xy plane and made an offset plane from it, placing this at the start of the timeline so I could use it as a new sketch plane.

Finally, I go through the four sketches, redefining each to use the offset plane. The first three are fine but the "Sketch facing +z" turns upside down (7:56 minutes) - I think it has revolved 180 degrees about the sketch x-axis. Actually it does this even if I redefine onto the xy plane (coplanar with the original face) - not in screencast.

Hopefully this demonstrates the problem and it will get fixed at some point to give a more "friendly" behaviour. Comments?

Re: Discussing the "Redefine Sketch Plane" problem

r.moss — Tue, 30 Jun 2020 15:37:40 GMT

Screencast 2 of 3 on this theme.

This explores the behaviour when using faces around a body. I start with a truncated square pyramid, so all the faces are identical; as before I have drawn a pair of sketches, one on the front face and another on a plane co-planar with that face.

Up to 5:52 minutes I am using the sketch that started on a face plane; after that I use a sketch on a construction plane.

Highlights:

2:39 face sketch redefined onto the z2 plane, turns upside down

4:15 redefined onto the x-80 plane, upside down

4:42 onto x_bl plane, turns anticlockwise 90

5:25 onto x_tr plane, turns clockwise 90 then 180 about what used to be the x-axis

6:68 (now starting from the z-10 construction plane), redefine onto z2, as 2:39 above

7:37 onto the x-80 plane (4:15 above) now OK!

8:15 onto the x_bl plane, turns clockwise 90

8:39 onto x_tr plane, turns anticlockwise 90 then 180 about what used to be the x-axis

(Sorry, Intel HD graphics, there's a shadow on the left side of the screencast).

Re: Discussing the "Redefine Sketch Plane" problem

r.moss — Tue, 30 Jun 2020 15:39:43 GMT

Screencast 3

This explores movement between differently inclined planes, starting with 4 identical sketches in the xy plane (front and back of the xy plane, front face of an extrusion, back face of an extrusion) and redefining them onto (a) a plane at 45 deg to xy, (b) a plane intersecting each of the origin planes at 45 deg.

The new sketch positions are unlikely to be what the user intended - none correspond to the obvious geometry choices mentioned above. As with the other screencasts, the sketch on the back face of the extrusion behaves differently to the others.

Re: Discussing the "Redefine Sketch Plane" problem

r.moss — Tue, 30 Jun 2020 19:01:19 GMT

Sorry - the forum interface has a bug and has posted 3 copies of message 3's screencast rather than a different screencast in each of my messages. The screencast links for the 3 messages are:

https://autode.sk/3i2LlS1

https://autode.sk/2BNZp10

https://autode.sk/3ihIhl6

Re: Discussing the "Redefine Sketch Plane" problem

lindsay.fowler — Wed, 01 Jul 2020 01:58:10 GMT

I think they should just store a vector that represents the direction the sketch was drawn from. Then no one would have any of this trouble.

Re: Discussing the "Redefine Sketch Plane" problem

Kzinty — Thu, 29 Sep 2022 20:22:54 GMT

Its been years now. Any chance Autodesk is going to deal with this? Changing features prior to the sketch plane also cause the failure of many features in the rebuild process and has caused me a great deal of money to fix models. I will have to start considering switching software if it is not dealt with soon.

Re: Discussing the "Redefine Sketch Plane" problem

TheCADWhisperer — Thu, 29 Sep 2022 21:45:51 GMT

@Kzinty

What software will you switch to?

Works the same way in SolidWorks, Creo and Inventor.

Issue is usually a result of violation of logical history.
Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

Whatever software you end up switching to - I recommend that you adopt the BORN Technique as much as possible and practical. This technique should eliminate this type of issue.

Re: Discussing the "Redefine Sketch Plane" problem

Kzinty — Fri, 30 Sep 2022 14:41:10 GMT

Actually, I likely won't switch because of the cost difference. I just get so angry with this aspect of the modeling and I had so few issues with rebuilds or redefining planes in SW in the 6 years I used it that I can't complain about that aspect of the software. NX never gave me issue either and I used that for 8 years. Now I have a small business and can't afford those options, but honestly, NX was the far and away leader of everything I used, also the most expensive.

When redefining a plane there usually are only 6 options for the orientation of the XYZ axis directions. Why not offer each of the solution options with NEXT, BACK and APPLY buttons? When the software cannot calculate the 6 options maybe because you picked a plane that is rotated 90 degrees it asks for 2 directions that are optional between XY and Z.

Re: Discussing the "Redefine Sketch Plane" problem

jlarsonLP454 — Fri, 15 Mar 2024 18:08:15 GMT

I just ran into this issue - I need to switch from a sketch on a face to a sketch on an offset plane and it comes in mirrored. Fusion team - please add in some UI controls when you are redefining the plane as Kzinty recommended above!