To set the posts vertical, I measure their distance apart at the base then G-clamp a piece of wood between the posts about halfway up. I adjust the clamps until the distance between the posts at the level of the horizontal piece of wood is the same as that at the base and using a spirit level ensure that the horizontal piece of wood is truly horizontal. I then push the posts from side to side, allowing them to pivot where they are clamped until the posts are vertical. I then clamp a diagonal piece of wood to ensure everything stays in place.
I repeat this procedure for all four sides. If I am running out of G-clamps, I put a temporary screw in and liberate the G-clamp.
Now I measure from the horizontal pieces of wood to the tops of the posts. I take the shortest post as my pattern and then I mark the other three posts to that measurement, climb up a pair of steps and trim the posts with a hand saw (or easier but longer, take the posts down and trim them on a Workmate).
Next, I mark out half joints on the 160 x 50 top beams, make saw cuts to the right depth at about 20mm spacing and chisel out the waste tidying up with a rebate plane where necessary.
I put two opposite beams on the tops of the posts and secure them with four off-centre wood screws (so they won’t get in the way of the coach screw main fixings). I then put on the remaining two beams. I secure them by drilling 10mm pilot holes about 75mm deep in the centre of each joint and spanner in 10 x 150mm hex-head coach screws with a large square washer under each head.
Link uprights with cross piece. Make sure uprights are same distance apart at base and cross piece.
Raise or lower cross piece to be level.
Get diagonal piece ready and push uprights until they are vertical
Clamp everything up tightly (or put in temporary screws). Do on all four sides. Measure from cross pieces to mark where upright tops need to be trimmed.
Cutting half joints in the top beams.
Clamp a guide in place and make the first cut (to half the depth of the wood).
Move the guide by the width of the wood less about half the width of the saw cut (to allow a small clearance).
Measure from a pencil line drawn against the guide in its first position.
Make the second cut against the guide then more cuts, freehand, between the first and second cuts.
Chop out the waste from both sides to avoid splitting off wood below the line.
Get the surface as clean as possible…
Then finish off with a rebate plane.
Plane from both sides to avoid splitting off wood.
Getting the uprights vertical
Putting the top beams in place
The beams are fixed to the uprights with 10 mm coach screws.