The first stage of making the arches involves cutting the “ears”, which support the ends of the arches.
Left below: cut a suitable length of treated 75 x 75 mm softwood. Centre below: mark the extent of the straight part of the cut which will make the “ear” shape. Left below: use a rip saw blade to make the straight cut. My 10 inch blade just about cuts to 75 mm depth.
Far left: use a template to mark out the curved section and, left: band saw it out.
I cut suitable lengths of 38 x 11 mm timber (ripped down from 38 x 25, selected to be as knot free as possible) and bend them in between the “ears”. I use three laminations and don’t bother to angle the cut ends. I paint the arch with preservative after construction and assume it will get into layers of the lamination. (I use clear, spirit-based stuff as I feel that gets into places the water-based preservative won’t - just based on a feeling!)
Below: I clamp the laminations together as I construct the trellis which will ultimately hold it all together.