To set sliding bevel to mark angles for the dovetail, draw a square line across a sleeper and mark a point 80mm from the edge. Along the edge, mark a point 10mm from the square line. Place body of bevel on the edge, swing the blade so it meets these 2 marks and tighten.
Cut a seat leg to length with power saw. Along 1 long edge of 1 end face, mark a point 40mm in from a corner. Use the bevel to draw a line from this mark across the face, angled towards centre of sleeper. Repeat for other corner on the same face.
Lay seat leg flat. Place an offcut of sleeper on its end flush with marked end of seat leg. Trace thickness of sleeper on face of seat leg. Turn over and repeat on other face.
Using combination square, draw a square line from where the angled lines on the end meet the edge to the line of the sleeper thickness drawn across the face. Repeat for the other face.
Clamp a sleeper to your bench then clamp the seat leg to this with marked end facing up. Cut on the inside of angled lines on the end with power saw. Finish cut with handsaw down to line across face.
Place sharp wood chisel on line across face and tap firmly with hammer to score timber along this line. Knock out a small amount of waste timber to expose this edge.
Using power multi-tool, cut vertically into seat leg along the scored edge. Knock out waste timber with chisel.
When half-way through, turn seat leg over and repeat Steps 6 – 7 to remove rest of waste timber. This will create socket and pins of dovetail.
Cut seat bench to length. Stand seat leg on seat bench so wide end of socket is flush with end of seat bench. Trace around pins. With combination square, measure to transfer shape.
Set power saw to correct depth and cut sleeper on each side of narrowest point of tail.
Check saw cutting depth for each side of tail, as accuracy is important to finished look. Cut from end of bench along sides of tail, flipping it over to cut both faces. Complete cut with handsaw to remove waste timber.
Spread glue on join and bring tail and socket together. Use hammer to knock 2 pieces together if required, protecting timber with a block. Repeat to attach another seat leg to other end of bench. Make sure legs are square to bench. Keep track of which socket was used to mark out which tail so they go back together at assembly.
Fit drill with 16mm spade bit. Drill through centre of tail into seat leg, to full depth of bit. Cut a length of 16mm dowel longer than hole. Glue and hammer in. Repeat for other end of seat. Leave to set.
Drill an 80mm-deep hole from 1 side through centre of pin into tail. Cut dowel slightly longer, then glue and hammer into hole. Repeat for other side of seat and other end. Leave to set.
Cut off protruding dowel flush with the seat.
Chamfer edges of seat with power plane held on an angle. Switch to orbital sander to get into corners.
Sand out any minor variations in joins with belt sander to smooth timber.
Create 3 table assemblies by joining table legs to table tops in same way as benches. Lay out table assemblies with legs upright, ends aligned and a 10mm gap between them. Fix 3 cleats to underside of table using 50mm batten screws. Screw 1 on inside of table legs at each end near bottom.
Apply a coat of dark exterior stain (Blackburn) to end grain on each side of dovetail. When dry, coat rest of unit in 2 coats of exterior stain in Silver Birch, allowing to dry between coats.