Lay two posts face up and parallel to each other on a flat surface. Position one arch piece into the notches on top of the posts and mark the location of the holes for the lag screws. Using a spade bit, first drill 7/8"- diameter countersink holes (to allow the head of the lag screw to sit flush with the surface), then drill 1/4"- diameter pilot holes. Insert the stainless-steel lag screws and washers and drive them in with a socket or crescent wrench. Repeat this process for the back arch and post assembly.
Next, lay one of the assemblies face down on the ground and position a side frame onto the corner post; attach with six 2 1/2" deck screws. Repeat for the other side panel, then lift the second arch and post assembly onto the top of the sides. Attach the frames to this with more screws driven in from the inside of the frame. Next, stand the arbour upright. Cut the crosspieces to length and attach them to the top of the arches with a single screw in each end. Finally, fill screw holes with silicone caulking to prevent water from seeping in and damaging the wood.
For maximum sturdiness, secure the arbour to four concrete footings that extend below the frost line with galvanized metal saddle brackets. For an easier, less permanent option, excavate about 12" of soil under each post, then fill the holes with coarse gravel for drainage.
(This method is more susceptible to frost heave; adjust if necessary by adding or removing some gravel each spring.)
Before applying any finish, prepare the surface of the cedar by thoroughly sanding with a 60-grit abrasive on a random orbit sander. For a formal look, apply two coats of white, opaque, oil-based stain. If you prefer the natural look of cedar, apply a few coats of semi-transparent, oil-based stain. Or simply let the untreated cedar weather to a beautiful, silver-grey patina.
- Paul Lewis designs and builds furniture from his home near Bradford, Ontario. See more of Paul's work at www.pushstick.com