I thing someboy just guessing to answer me that this is impossible.
Unfortunately I know this. The matter is we are doing some lines in ours drawings, but when we try to fillet them, they are non coplanar, even they are Z-0 lines!!!.
Anybody knows why is happening??, do we need to set some kind of variable in order to fix this problem??.
Sometimes we got to do the lines again, and sometimes fix the problem that...
First, set your display accuracy to the smallest increment for the units your are using, then list the objects to determine the Z values. If display accuracy is set too high values round off to zero when they actually are some other value.
If both line endpoints were at Z=0, they would fillet as expected. One or both endpoints are not where they should be.
You should open your view toolbar and select the front view and make sure nothing is drawn on another plane. If there is you can use the flat.lsp that I have attached to put everything in the drawing on the same plane. You may have to do it a couple of times.
George D: You are quite right. If you note in the OP's post, he said endpoints were at zero. Since we know that can't be, I suspect he's got his dosplay accuracy setting set too high and it's not displaying perhaps a fractional Z value.
The other option if he wants to fillet "as-is" is to draw a 2 point circle between the end points align his UCS and fillet but this won't work if conditions are as you describe.