I use 3d sketches regularly, creating geometric wireframes, from which surfaces are created. The 'future' surfaces must be planar. Clearly, any surface that is formed only from a triangle is already planar. But a quadrilateral, or with more edges, isn't inherently planar.

My 'standard' method to guarantee planarity is to sketch the diagonals, and then to make the two diagonals coincident at a point. It works, often with a great struggle to get SW to recognize the coincidence, since it doesn't always see how close the two lines/points actually are unless I drag them together. It's like coercing toddlers to make friends.

Another method I have tried is to close the 'base wireframe', create a plane on three of the wireframe points, draw a 3d-planar quadrilateral on that plane, detach the coincident points from the underlying wireframe, send my planar-3d sketch back in time before the wireframe, and then reattach the 3d wireframe onto the planar quadrilateral. Very involved and difficult to do on several adjoining surfaces.

I've attached a JPG showing roughly the sequence I go through... wireframe, triangular surfaces, quad surfaces, and pic 4 and 5 clearly show the non-planar quad. 6 shows the warped wireframe, 7 shows my diagonals, and 8 shows a failed constraint assignment, before I drag the two lines close enough to mate (not shown).

I need a better way to constrain my 3d wireframe's quadrilateral points to a plane, without an actual plane to place them on.

Is there some kind of virtual 'on-plane' constraint, or some way to create a temporary plane, while in the midst of a 3d sketch? I don't see how '3d-sketch-on-a-plane' can help me, but I'm open to all suggestions.

TIA, Doug

I've found a solution... one I perhaps should have known about, but had never seen, nor was ever taught about it in the many courses I've taken since SW98PLUS.

'PLANE' in the sketch menu. That provides exactly the tool I needed, in the midst of creating a 3d wireframe sketch. I can put down four points in space, then define a plane around three of the points, and then constrain the fourth point 'ON PLANE'.

It does still take some manual tweaking-dragging-placing-unconstraining-reconstraining of the point on the plane. It still confounds me why SW can't find a perfectly obvious relation between a point and a plane ('ON PLANE' or 'ON SURFACE' ) unless the user drags the point to a location somewhere around .01 away from the plane.