Building an arch-top arbor
Arch-top arbors are classic and beautiful, especially when roses are climbing up the sides and over the top.
- MAKE A TEMPLATE WITH A ROUTER JIG
- DRILL FOR THE ROUTER
- ATTACH HARDBOARD TO A WORK SURFACE
- ROUT ONE EDGE OF THE ARCH
- CUT THE STOCK FOR THE ARCHES
- CUT OUT THE ARCHES
- SUPPORT THE POSTS
- ATTACH THE TOP PLATES AND SLATS
- LAY OUT AND DIG HOLES FOR POSTS
MAKE A TEMPLATE WITH A ROUTER JIG
Make a template of the arch with the help of a jig that turns your router into a giant compass. Cut a 40-inch piece of 1/2 –inch plywood to a width of 10 inches. Drill two 1/16-inch-diameter holes in it: one centered 6 inches from the end and the other centered 4 inches from the first hole. Drill a centered ½-inch-diameter hole 24 inches from the first hole.
DRILL FOR THE ROUTER
Unscrew the router base, put a ½-inch bit in the router, and put the bit in the ½-inch hole. Put a pencil through the screw holes in the router base and mark the plywood. Drill stepped holes at each mark: drill 3/8-inch-diameter holes ¼ inch deep, then drill 1/8-inch holes that go all the way through the plywood in the center of the first holes. Screw the router to the jig through the holes you just drilled, propping up the unsupported end of the jig to make the job easier. (You may need to replace the original screws with longer ones.) if the screw heads stick out above the surface of the plywood, make the holes slightly deeper.
ATTACH HARDBOARD TO A WORK SURFACE
Screw the corners of a sheet of tempered hardboard to a sheet of inexpensive ½-inch plywood. Draw a line across the center of the hardboard, dividing the sheet into two 48-inch squares. Accurately drill a 1/16-inch hole in the center of the line. Drive a #8 drywall screw through either of the holes in the jig into the 1/16-inch hole in the hardboard until just snug so that the jig will turn smoothly but not wiggle.
ROUT ONE EDGE OF THE ARCH
Lower the router bit to barely cut through the hardboard. Swing the jig so the bit is just to the left of the edge of the hardboard. Turn on the router and swing the jig across the hardboard in a slow arc. Put the screw in the other hole and screw the jig back in place. Drive in a couple of drywall screws to hold the arch in place once you cut it free. Make sure the router won’t hit any of the screws, then rout out the arch. Cut the ends of the arch along the pencil lines you drew in step 1.
CUT THE STOCK FOR THE ARCHES
For stability, each arch is made of three layers, each made of 1x8s and trimmed to shape. Lay out an inner layer and two outer layers for each arch using the dimensions given above. The angles are 25 degrees if cut on a tablesaw or power miter saw and 65 degrees if you use a protractor. Stack up the parts for each arch and lay out the arch on each stack. Glue the layers together with construction adhesive, then nail the layers together wit h4d finishing nails placed well away from the layout lines.
CUT OUT THE ARCHES
Cut along the layout lines wit ha saver saw. Cut slowly and carefully, skimming the outside edge of the line as you go. You’ll clean up the cut later with your router and a flush trim bit. For the smoothest possible curve, rout the arch to shape using the template you made earlier as a guide. Wipe the dust off the arch, cover it with two-sided carpet tape, and press the template firmly in place over the tape. Drive finishing nails at the top and sides to secure. Put a flush trim bit in the router-a bit with the bearing on top will be easiest to use. Clamp the arch so it overhangs a work surface and guide the bearing along the template to trim edges of the arch. Leave the ends of the arch as the saw cut them-if you try to rout them, the wood will split.
SUPPORT THE POSTS
The arch will be somewhat flexible until it’s anchored in concrete. To support it, cut some leftover plywood into 3x4-foot panels and screw the panels to the posts.
ATTACH THE TOP PLATES AND SLATS
Measure the width of the side, subtract the combined thickness of the arches, and cut a 2x4 top plate to this length. Screw it to the tops of the posts as a support for the arches. Cut 1x3 slats to length and screw each end to the posts with two screws, spacing the slates 8 inches apart on center. Repeat on the second side. Remove the plywood. Put an arch in place and screw it into the 2x4 top plates. Measure to make sure the legs are parallel, then screw a brace across them. Attach the other arch and attach the slats.
LAY OUT AND DIG HOLES FOR POSTS
Dig the holes 3 feet 4 inches deep. Shovel 4 inches of gravel into the holes, tamp, then put the posts in the holes. Check that the posts are plumb, then brace them. Prepare pre-mixed concrete in a wheelbarrow following the directions on the bag. Add water a bit at a time and mix with a mason’s hoe until the concrete clings to the hoe when you lift it. Shovel concrete into the postholes. Work a 2x4 up and down in the concrete to eliminate air pockets. Slope the top of the concrete so water drains away from the posts. Allow the concrete to cure for two or three days before removing the braces.
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