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AW Extra - Garden Arbor


An Elegant Structure with Super-Strong Joinery


by Tim Johnson






Here’s a project that’s guaranteed to add romance to your garden: an inviting gateway that promises beauty and tranquility to all who pass through.


Building this arbor is a big undertaking, because of its complex design and grand scale, but it isn’t a difficult project. All the parts go together with simple joinery and basic tools. 


The arbor’s components are modular. You build them in your workshop and then assemble the arbor on site. The posts will stay straight because they’re glued-together hollow boxes. These lightweight posts are much easier to lift and maneuver than solid posts. You’ll create sturdy structures with strong joints by stacking and gluing pieces in layers. You’ll fashion attractive curves and stylish ogees. Best of all, when you’ve found the perfect spot, I’ll show you step by step how to install your arbor there. 


You can build this arbor in No. 3 cedar for about $500. Omitting the gates saves $100. I built the Cadillac version you see here using D-grade cedar, which has very few knots. D-grade cedar is expensive and usually isn’t available at home centers. I had to go to a full-service lumberyard to find it, and I spent nearly $1,100. 


Knots are common in No. 3 cedar, so using it will make the arbor look more rustic. Knots also make No. 3 cedar harder to work with, so select boards with the fewest knots. 


Cedar is sold as dimensional lumber (1x4, 1x6, etc.). I bought rough 1-in. stock. It comes with one side surfaced and is usually about 7/8 in. thick. I milled all my 1-in. cedar down to a 3/4-in. thickness by surfacing the rough side. The 2-in. cedar came surfaced on all four sides (S4S), milled to a 1-1/2-in. thickness. I cut off the rounded-over corners on the S4S cedar.



Build the Side Panels


The side panels (A, Fig. A, below) are three-layer sandwiches, with vertical pickets (A1 and A2) held between horizontal rails (A3 through A6). Assembly is easy because the pieces are simply stacked, glued and screwed. The top rail is three layers thick. Its inside rail covers the tops of the pickets to protect the end grain. The other rails are fastened to the outside, so moisture can drain between the pickets. Glue these panels together on a flat surface, so they aren’t twisted. Use waterproof glue.


1. Cut all the pieces to width.


2. Cut the rails and the two outer pickets to length, with the ends squarely cut.


3. Make patterns for the curved profiles in the top rails (Fig. B, below) by swinging arcs on 1/4-in.-thick scrap stock and bandsawing. Use the patterns and reference points A and B to transfer the arcs to the top rail blanks (A3 and A4). Then saw out the rails.


4. Glue and screw the inside top rail to one of the outside rails. Make sure the ends align and the glue joint is tight. Remove any squeezed-out glue.


5. Tack the frame together (Photo 1). The two outer pickets protrude beyond the rails by 3/8 in. to form tongues (Detail 1, below). Draw layout lines on these pickets to indicate the ends of the rails. Lay the pickets on the top and bottom rails. Butt the pickets against the inside top rail and align the other ends with the bottom edge of the bottom rail. Apply glue and tack the corners.


6. Square the frame and then screw it together with 1-1/4-in. deck screws. Drill countersunk pilot holes first, so the screws don’t split the wood. Work fast, so you finish before the glue sets up.


7. Use your layout lines to attach one middle rail to the bottom side of the frame. Make sure its ends align with the top and bottom rails.
8. Install the inner pickets, using 2-1/2-in.-wide spacers (Photo 2). Cut the pickets to length as you go. Fasten them with glue and screws in predrilled holes. 
9. Glue and clamp the remaining top, middle and bottom outside rails. Make sure the ends align.
10. Smooth the curve on the top rails using a belt sander or a sanding drum chucked in a drill.

Build the Posts


The posts (B) are hollow, made from four pieces that are simply butted, glued and clamped (Photo 3).
11. Cut the post pieces (B1 through B3) to width and length. The sides are narrower, so butting them between the front and back pieces creates a square post.
12. Glue and clamp the sides to the back piece. Remove any squeezed-out glue.
13. Glue and screw a block (B4) to the back side of the front piece.
14. Glue and clamp the front piece to complete the post; make sure the bottom edges are flush. Remove any squeezed-out glue.
15. Rout a stopped groove in the back of each post, centered and sized to fit the side panel’s picket tongues (Photo 4). Square the bottom end of each groove 4 in. from the post’s bottom edge. 

Glue Up the End Assemblies


Each side panel mounts between two posts with tongue-and-groove joints (Photo 5). These end assemblies are large, so enlist a friend to help. Work on a flat surface, so you don’t glue a twist into the assembly.
16. Lay the posts on top of three pipe clamps, spaced far enough apart for the side panel to fit between them. Position the clamps so they’ll be right under the side panel rails.
17. Position the side panel between the posts. Set it on blocks, so the picket tongues align with the grooves.
18. Test-fit the joint. Add three clamps on top of the posts, directly over the panel rails, and slowly draw the joint together. Square the assembly by making sure the panel sits 4 in. from the bottom of each post. Apply even clamping pressure above and below each joint. The panel’s rail shoulders should fit tightly against the posts.
19. Disassemble the joints, apply glue to the tongues and grooves and draw the assembly back together. Remove any squeezed-out glue. If gluing both tongue-and-groove joints at once is too nerve-wracking, glue one joint at a time. 

Make the Beams and Rafters


The beams and rafters (C and D) lock together with half-lap joints. The notches have to be located precisely, so the assembled beams and rafters will fit properly around the posts at the top of the arbor. 
20. Cut the beams and rafters to width and length. 
21. Clamp the two beams together and lay out the two outer notches (Detail 2, below). Make sure the ends of the beams are flush. Otherwise, the notches won’t line up correctly. Lay out the inner notches. They’re evenly spaced between the outer notches.
22. Cut the notches using a circular saw, with the blade set to cut to the bottom of the notch (Photo 6). Use a chisel to clear the waste and smooth the bottom of the notches (Photo 7).
23. Gang the five rafters together and cut the notches in them the same way. The rafters have only two notches; they’re 40-1/4 in. apart. 
24. Make a pattern (Detail 2) and mark the ogee profiles on the beams and rafters. On the beams, the notches are at the top; on the rafters, the notches go at the bottom. Saw out the profiles (Photo 8).

Build the Gates


The gates (E) are layered, just like the side panels, but they go together differently and feature robust mortise-and-tenon joints.
25. Cut the hinge and latch stile components (E1 through E4) to length and width. Cut the loose tenons (E5) to size, too. The last 1-1/2 in. of their top edges slope 1 in. to shed moisture.
26. Glue the hinge and latch stiles by sandwiching an inside stile and a loose tenon between the outside stiles. Keep all the pieces aligned and the edges flush when you clamp. It helps to tack the pieces in place as you stack them together. After clamping, remove the squeezed-out glue—don’t forget the bottom of the mortises. After gluing, you’ll have three-layer stiles with flush edges, open mortises at the top and tenons protruding from the bottom.
27. Cut the bottom gate rails (E8) to width and length. 
28. Make an arched pattern for the outside top gate rails (E6, Fig. C, below). 
29. Cut blanks for the outside top gate rails. Cut the ends of these blanks at 70-degree angles, spaced 18-3/4 in. These angled top rail blanks must be the same length as the bottom rails. 
30. Use reference points A and B on Fig. C to position your pattern on the blank. Transfer the arches and cut out the rail. 
31. Make an arched pattern and cut the blank for the inside top gate rail (E7, Fig. C, below). This rail extends beyond the outside top rails to create the tenons. Cut the ends of this blank at 70 degrees, spaced 25-3/4 in. This rail is as long as the gate is wide. 
32. Use reference points A and B on Fig. C to position your pattern and transfer the arches. Establish the two tenons by extending lines at 90-degree angles from the edges. Cut out the inside top rail.
33. Glue the inside top rail to one of the outside rails.
34. Glue the gate frames together (Photo 9). Clamp one bottom rail between the stiles, under the protruding tenons. Apply glue inside the mortises at the top of the stiles and to the tenons on the two-layer top rail. Install the top rail. Make sure the gate is square. Clamp the mortise-and-tenon joints at the top and glue and screw the tenons to the bottom rail.
35. Install the pickets (E9), using spacers, and fasten them with glue and screws. Then glue and clamp the remaining top and bottom rails. 
36. Seal the exposed end grain on the tops of the gates with epoxy or thinned waterproof glue.

Install the Arbor


37. Install the anchor posts (Photo 10). Treated timbers are never straight. So that they’ll seat flush inside the hollow posts, joint adjacent faces of each 4x4 to create a flat, square corner. Rout a clearance chamfer to avoid hardened glue inside the post. Slide the 4x4 halfway into the hollow post, leaving 36 in. exposed, and fasten it to the inside corner with 2-1/2-in. deck screws on both sides (Detail 3, below). For longest life, orient the 4x4s so the “factory” ends go in the ground and the ends you’ve sawn go inside the posts. 
38. Determine the arbor’s position in your garden and dig 8-in.-dia. x 40-in.-deep holes for the posts. First, drive a stake to mark the center of each hole. Establish the holes by spading down about 6 in. on all four sides of the stake. Then go to town with a post-hole digger. Using a level, determine the ground’s slope and mark the hole that sits at the highest grade.
39. Install the first end assembly (Photo 11). Plumb the post that goes in the hole at the highest grade (Photo 12). Starting with this post assures that all four posts will be above grade. When the first post is staked in position, level the assembly front to back (Photo 13). Then plumb the second post.
40. Use this staked assembly to install the other end assembly level, plumb and square (Photos 14 and 15).
41. Install the beams and rafters (Photos 16 and 17). Fasten them to the posts with screws and plugs.
42. Screw on the post caps after sealing the joints with silicone caulk (B5, Photo 18).
43. Fill and tamp the post holes (Photo 19).
44. Make and install the post trim (Photo 20).
45. Install the gates (Photo 21). Make sure the gap between the gates is large enough, at least 1/4-in., so they swing freely. Install a latch to close the gates. I used a large hook and eye screw combination mounted on the back of the gates for appearance. To hold the gates open, I installed a second hook to one side panel and a second eye screw to the other.
46. If you want to maintain the look of the fresh cedar, apply a finish. I used Penofin’s Western Red Cedar exterior stain. You should plan to recoat any exterior finish biennially. Without finish, the cedar will weather to gray within one or two seasons. 




Photo 1: The side panels are layered like a sandwich. Lay the outer pickets in position on top of the rails to make the frame. Apply glue and tack the pieces together with a pin nail in each corner. Square the frame by adjusting it until both diagonal measurements are the same. Then screw the stiles to the rails.






Photo 2: Position the inner pickets, using spacers, and then fasten them with glue and screws through predrilled holes. Remove the spacers and complete the side panel by gluing and clamping the outside rails.






Photo 3: The posts are built as hollow boxes. They weigh a lot less than solid timbers and are more stable. The front piece is shorter, creating a ledge to support the arbor’s horizontal beams. The attached screw block anchors the beam’s mounting screws.






Photo 4: Rout a groove on each post’s back face, sized to fit the protruding pickets on the side panels. Tongue-and-groove joints secure the side panels to the posts.






Photo 5: Glue each side panel between two posts. These end assemblies are about the same size as a 4x8 sheet of plywood, so before you glue, make sure you’ll be able to move the glued-up assembly out of your shop. 







Photo 6: Cut notches in the beams and rafters. Clamping the pieces together allows you to cut perfectly aligned notches. Use a speed square to make straight cuts. Establish the shoulders first. Then make cuts in the middle until only thin pieces remain.







Photo 7: Clear the waste by twisting a chisel against the thin pieces. These pieces break out easily because of their short grain. After you’ve removed the waste, clean up the bottoms of the notches with your chisel.







Photo 8: Saw profiles on the ends of the beams and rafters. First, cut the curve. Then cut the straight shoulder. Hold the waste piece while you cut, so it doesn’t tear away. 







Photo 9: Glue the gate together. Apply glue, assemble the frame, square it and clamp the joints. The layered stiles and upper rail are glued together prior to assembly. After you install the pickets, glue and clamp the remaining top and bottom rails. 







Photo 10: Anchor the arbor with treated 4x4s fastened inside the posts. This construction method assures long life, because treated lumber lasts much longer underground than cedar. 






Photo 11: Slip one end assembly into the holes you’ve dug. Even though this assembly is huge, it’s easy to maneuver, because it doesn’t weigh much and isn’t top-heavy. 







Photo 12: Plumb the first post. Raise the end assembly on blocks, so the bottom edges of the cedar rest a couple inches above the ground. Stake the post in position, using a level and a diagonal brace.







Photo 13: Level the assembly with shims. Then plumb the second post and stake it in position, using a second diagonal brace. With this end assembly plum, level and staked, you’re ready to install the other one. 






Photo 14: Install the second end assembly on blocks and level it with the first, side to side and front to back. You’ll need two levels, a pair of long, straight boards and more shims.






Photo 15: Plumb the second end assembly by fastening it to the first with braces top and bottom, each cut to match the arbor’s width. Measure the diagonals and make adjustments until the base is square. Then install a diagonal brace to keep it there. 






Photo 16: Clamp the beams in position by replacing the upper braces one at a time. Rest the beam on the posts’ built-in ledges. Align the notches with the side of the posts.






Photo 17: Install the outside rafters. Supported by the half-lap joints, they nest against the sides of the posts. Install the inside rafters last.






Photo 18: Cap the posts to cover the end grain. Form a weather-tight seal with silicone caulk. Fasten the caps with screws. Left unprotected, end grain wicks moisture, which accelerates decay.







Photo 19: Fill the post holes with pea gravel. It’s much easier to use than concrete and less messy. Tamp the gravel around the posts to securely anchor the structure.






Photo 20: Install trim with galvanized pin nails and waterproof glue. Countersink the nails and fill the holes with exterior-grade putty, so you don’t end up with black stains from contact between metal and moisture.






Photo 21: Install the gates. Clamp them flush with the back faces of the posts, using shims at all four hinge locations to establish even gaps all around. Then screw on the hinges.



















This story originally appeared in American Woodworker May 2005, issue #114.

Source information may have changed since the original publication date.






May 2005, issue #114

Purchase this back issue.






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