The said:
Best way to do end to end joints in 4 x 2 ? In other words to make 2 x
2.4's into a 4.8 ish length.
I was thinking either lap joint & glue & bolts or those spiky washer
things - joint doesn't have to be in line, just resist deflection. Timber
on edge.
lap and timber connectors would work and probably be more than adequate
for a deck.
Alternatively a longish scarf joint, with bolts through the verticals.
(Same technique as can be used to extend a ridge beam in a roof).
You can either do the simple one with a 1 in 8 to 1 in 10 slope on the
timber, glued up and bolts either vertical (or drilled at an angle so as
to be perpendicular to the scarf).
(counter sink the nut and bolt if you want a flat profile):
B B
----------------------------------
/
/
/
--------/-------------------------
B B
(bolts at B)
The stronger one, uses a profile like:
________________________________
\
/
/
/
________ \_____________________
The sloped cut is the same, but does a 90 degree turn a little way in
from each edge on top and bottom. Once glued and bolted this is better
at transferring the bending moment into compressive forces on the top of
the joist, and reduces the shear loading on the glue line.
The first is easy to cut on a SCMS, the latter requires a stopped cut so
is best done with a handsaw or a decent jigsaw. (you cut it in three
goes - the slope from one side to the change in direction at the other
edge, then the cut from the far edge to meet the slope, and finally trim
off the sharp point).
