Bernie,
Here are a couple of suggestions for you to consider...
1) As A-Dubya says, do a mock-up;
2) Drill holes through your tenons at the bottom of your wedge kerfs. The
drill diameter should be slightly wider than the width of your kerf;(helps
keep your stock from plitting outside the mortice later)
3) Make your mortice shoulders slightly angled outward, to compensate for
the spread of the tenon when the wedges are inserted and the tenon drawn
closed;
4) Make the thickest part of your wedges the width of the kerf plus the
angle of one of your shoulder angles;
5) The wedges at their thinnest part should be the width of your kerf...
maybe just ***a tad*** thinner.
6) The wedges should be a little shorter than the length of your kerf.

When the joint is drawn closed, the hole helps prevent splitting of your
rails outside of the tenon. The shoulders of the tenon will spread apart and
fill the mortice.

Don't shy from this joint...it's a good one and it'll work if you take the
time to watch carefully the widths of wedges and the shoulder angles in the
mortice. Practice a joint or two on some scrap stock.

Good luck
Larry

--
Americans

"Bernie Ross" wrote in message
...
Building a bed for my 6-month-old, who will soon have outgrown his crib.

I'm thinking of trying to use "fox tenon" joints, whereby a couple of
slots
are cut in the tenon, small wedges are placed in the slots, and as the
tenon
is driven into the mortise, the tenon expands, giving a very tight fit
indeed.

As I understand it, if you make the wedges too long, the tenon shoulders
won't reach the piece with the mortise, and you'll never get the thing
out.
You only get one chance to get it right.

I've never done anything like this before. Any tips? I'm intending to
use
beech, if it makes any difference.

- Bernie