Hi Chris

I get this every so often when trying to use Boolean/ Union. The work arounds that I try are;

1) Select just the top faces of the the smaller items, i.e the r + w, make and paste a copy and then delete the solids, re-rextrude the surface (making sure that you extrude it into the other item, not just to a supposedly touching surface) and try "union" again, one small item and the big item at a time. When doing this, the R joined in to the main solid with no problem. The W wouldn't. So try next work around

2) What I do is select the new small solid and move it a fraction, and back again. Then try "union" again. Sometimes that works.

3) If 2 doesn't, as in the case of the W, move it a tiny amount (literally only a fraction of a mm) and try "union" there. In this case that worked.

Why this happens, I haven't a clue, but these work arounds have saved me pulling my hair out more than once. Of course if you have to match 100% exact diagrams, work around 3 would not be usable.

Andrew