In article , no, duke of wellington,.. wrote:
Hello, I am trying to join purple heart and African ribbon mahogany.
The edges have checked in a few places on the ph and the joint is
separating after only two days. I wiped with acetone and glued using
west systems 105 epoxy with a little sawdust and fastened with sheet
rock screws. The wood lives in an unheated shop in a damp climate. I
mill and glue, then move it into a small heated room to dry. I shape
and sand and then the work has to sit a few days until the ph turns
purple again but when I came back the project had failed. What am I
doing wrong?

1. Storing your wood in an unheated, damp area.
2. Milling it before it dries.
3. Gluing it before it dries.
4. Not waiting long enough for it to dry.
5. Using sheetrock screws. You want wood screws for joining wood; a wood
screw has a section of its shank that is unthreaded, so that the piece being
screwed through will be drawn down tight against the piece being screwed
into. When you use a screw that is threaded the full length of its shaft, the
screw threads can interfere with pulling the two pieces of wood tight against
each other.
6. If a joint is properly milled, glue and clamps will be sufficient anyway,
and you don't need screws.
7. It's not clear from your description, but I wonder if perhaps you're
attaching these pieces with the grain of the mahogany perpendicular to the
grain of the purpleheart. If that's the case, then another part of your
problem is using glue at all. Wood shrinks across its width as it dries,
perhaps considerably (depending on wood species and moisture content) -- but
shrinkage along the length is near zero. If you glue one board crosswise to
another, you've almost guaranteed that something's going to break as the
moisture content changes. Such joints need to be made with screws *only*, no
glue, and the screw holes at the ends need to be elongated to allow for wood
movement, e.g.
___ ___
(___) O (___)

The latest issue of Fine Woodworking has an excellent article on making table
tops, which describes all this in much more detail.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.