Trouble converting triangles into quads

I am new to Blender (using it for about a month) and have no prior experience using 3D animation software. I thought I’d have a go at the Robot model in the new Blender on-line PDF magazine and got stumped far too quickly…

Below is a descriptive version of my problem. However the long and short is this… sometimes Alt-J works (to convert triangles into quads) and sometimes it doesn’t. What gives?

I have a UVsphere, remove 2 adjacent vertices to make a square hole, then take the 3 vertices at each corner and press F to then give me 6 sides total. I take the inner 2 vertices of each of the new edges and subdivide (w>subdivide). I then get 2 triangles which I want to convert to a single quad. I select all 4 vertices and press Alt-J and sometimes it works, and sometimes it does not, even when I am pressing the same buttons in the same order for each of the corners. It appears to work for some edges all of the time and others none of the time. What gives? I am using a decent mac (imac G5) if that makes any difference.

Any help appreciated. Thanks

If three of the verts are almost in a line Blender sometimes thinks that it is a concave quad due to rounding errors so the face command won’t work . You have to move a vert before the face will be created.

GreyBeard

I am experiencing the exact same problem. Any help would be much appreciated. I am using 2.40RC1. Thanks!

Wow. Posted at the exact same moment. That worked perfectly. I moved the vertex that was created by the subdivide and moved it just barely. Thanks GreyBeard!

Another thing you can try is to delete the edge that separate the two triangles and press F to create face.

Thanks for the help Greybeard. I will give it a go when I get back from work. I too thought of your idea cipix (select the dividing line, delete it and then create a new face). However what I needed essentially was a triangle with one of the sides defined by 3 vertices but with each vertices only connecting 2 edges. If you delete the dividing edge, you also lose that 3rd vertex.

J

Not if you only delete edge (from X menu - Edges)