This is something that I’ve wondered for a while now. Why sometimes when you select 4 vertices to form a face does Blender insist on using 2 triangles instead of a single face?
I assume it’s something to do with the angles being too sharp, but I haven’t found a way to fix it. When trying to tidy up a mesh this can really slow things down 
Could that be because those 4 vertices does not form a plane? 3 vertices always form a plane, but 4 may or may not.
Side note: This is why photographers use tripods 
Thanks,
hmm: a quick question… is there a “make planar” command to move selected vertices onto a plane?
if someone has a script for this, it would also be good…
aersoy is right.
Imagine two 2 vertex lines perpendicular to each other. They simply can’t form 4 vertex face, there are only two 3 vertex faces to form.
Only solution is to move one vertex, make the face and move the vertex back. (a bit lenghty if one has to do it often)
Leon, to align vertixes in one line or one plane select them and scale them down to 0 while holding the MMB (or Alt+LMB, for a two button mouse).
MMB will restrict scaling to one axis, depending on the movement of the cursor.
The 4 vertices don’t have to be in the same plane since Blender will cheath his way out of it with to quasi-tris and soft shading. Make a simple plane, erase it face, move one vertice out of plane and press Fkey : it will be filled.
More likely, the 4 vertices are more than 4 : do a remove double with everything selected.
Jean
when rendering with faces in “solid mode” (default) faces are lit and drawn as triangles.
if the face is smoothed (set smooth command in edit buttons) the edge is not visible.
It is easier to convert a non-planar quad into triangles because it alleviates the problems with being able to see both sides of the face at once.
So there’s no way Blender will automatically do this for you? or is it a flaw in the modeler?
A 4 sided face can exist in any orietation in Blender. So it’s kind of annoying it can only be created in certain ones. Working around this is a major time sink when using with complex models
Just a note that the reason I’m doing this is to get rid of all the triangles from my mesh. Having quads and triangles in the same sub-surf’d mesh causes a whole load of irregularities. It’s a tedious process lengthened greatly by this problem.
Thanks for the replies btw 
I take it from those so far there is no override command to stop Blender doing this.
only works if you want to align on a global plane (XoY, XoZ, YoZ), doesn’t help with rotated faces.
Shouldn’t be too much hard to code though, I just wonder if it’s a worthy addition (maybe as part of a new Align With menu or whatever).
Martin
Ummm, you are pressing F, not Shift+F, aren’t you…
if that doesn’t help, use JKey to turn 2 tris into a quad
Does the JKey thing have to be in a specific mode? I can’t get it to work.
I guess I’ll use only triangles for future models, quads just aren’t worth the hassle.
You have to be in editmode, and you have to have the triangles selected.
I’ve heard that for some people J doesn’t work, but Ctrl+J or Alt+J does - try messing around with them
I also have this problem once in a while - usually with very acute quads on heavily edited meshes. A solution that I have found that usually works is to select all verticies in the mesh and do a Xsort. I can then create the quad in the normal manner – seems to clear up the glitch. Hope this helps 
Were can I found the ‘Extrude to face’ (or extrude to surface) function?
Thx,
Khiraly
Were can I found the ‘Extrude to face’ (or extrude to surface) function?
select the face, i.e. vertices of the face,
‘E’ for extrude, confirm,
and then Alt-S and drag.
Points should go in the direction of the face. If it doesn’t work the way you expect, don’t confirm the move and then go to a different view and repeat until you find the view that works for you.
I just did an experiment with a face that faced the side view and was successful using Alt-S in the top view.
Hope this helps,
PamTango