Cedar Potting Bench
A potting bench is an ideal accessory for your patio or back yard shed, providing a convenient place to seed flats of trays in the spring, or pot-up larger plants later in the summer. The wood you choose will be influenced by its final location. Pine or red oak would be ideal if your workspace is indoors, while cedar or white oak are more weather resistant and are a better choice for a bench that will be used outdoors. The bench would also make a great workspace and serving table next to your barbecue.
This bench is made of cedar, with all of the parts being milled from deck and fencing lumber – readily available from most building supply centres. When choosing your material, try to find pieces without knots and with tight vertical grain. When planing dry cedar, knots can easily take a chunk out of your knives, as well as becoming a weak spot in the finished board.
This project is fairly straightforward, no fancy joinery or complicated techniques to learn. The potting bench could be built in two configurations – permanent or knockdown for seasonal storage. Additionally, there is not one piece of metal used that would eventually rust and stain the bench. The secret is in using dowels to assemble all of the components. If you don’t glue some of the dowels and substitute a hard dense wood for a couple of the components, the bench can be easily disassembled for storage during the winter.
Using dowels to assemble a project is every bit as strong as mortise and tenon in everyday use, and they speed up the construction process considerably. Not having to allow additional length for tenons, will speed up the process and using a stop block when cutting multiple parts to length will assure you a square assembly. All this takes is careful lay out and accurate drilling of dowel holes. At first glance it looks like a daunting task, as there are 192 dowels in this project, which means that you will have to drill 384 holes in various pieces – and each must line up perfectly with its mate. The secret to lining all of these holes up is to always work from the same two reference faces when laying out and drilling the holes. When laying out holes manually, work from the same two common reference faces on each half of the joint and use a story stick to establish the distance between the dowels on a centerline (see Story Sticks, February/March 2006 issue # 40). Drilling these holes without a guide in softer woods like cedar can be problematic. The bit will tend to wander in both end and flat grain as the tip moves from softer summer growth to the harder winter growth. I much prefer building projects rather than spending hours laying out and drilling holes so I opted for a commercially available jig to simplify matters. (See Sidebar: Get Your Holes in a Row)
Shelf runners to the top board. Use this board to mark the others. This becomes the first reference edge.
Build End Frames
• Begin by milling the lumber for the legs (A) and end stretchers (B) and cutting the pieces to length. Select and mark the best faces for the front side.
• Mill the stock for the end slats (C) and use a stop block to cut the four pieces to exactly the same length.
• With all of the parts for the ends cut, lay them out with the best faces forward as they will be assembled. The bottom of the lower stretcher is 6 ¼” up from the bottom of the leg. Use a square to draw a reference line across the two inner faces of the legs. These lines, as well as the underside of the bottom stretcher, are one of the two required reference faces for this joint. The inner side of the leg and the inside face of the stretchers are the other.
• Lay out and drill holes for two dowels at each joint. Repeat this for the top stretcher. Again, the inside faces of the leg and stretchers are one reference face, but this time the other reference face is the top of the leg and the top side of the stretcher.
• Chamfer the four long sides and bottom of the legs with a 45º bit on a router table. Chamfering the bottom prevents chunks from tearing out of the legs as the bench is moved. Also chamfer the long edges of the end stretchers.
• Use a band saw to cut a ¾” x 3 ¼” long notch out of the top ends of each end stretcher to receive the shelf runners (F).
• Assemble and clamp the end together to be sure everything fits. You don’t want to get glue on everything and then find out that the clamps won’t pull it tight because one or more holes were too shallow for the dowels. (See Sidebar: Successful Dowel Gluing). If everything is fine, take it apart and sand the pieces for finishing. Apply a coat of tung oil to all surfaces. With the parts finished, assemble the ends with glue and clamp.
The Middle Bits
• Mill the front and back stretchers (D) and cut them to length. Use a stop block – they must all be exactly the same length.
• Mill the four pieces for the back slats (E), also using a stop block to cut them to length.
• Lay out the back slats in a similar pattern to the ends, and lay out and drill the holes for the dowels. Be careful not to end up with the stretchers offset, or your final bench will have either a lean or a twist. In both cases the row of holes is centered on the thickness of the piece.
• The front and rear stretchers are dowelled to the legs using four dowels at each joint. The bottom of the lower stretcher is 6 ¼” from the bottom of the leg. Use a square to mark this location on the inside edge of all four legs. This, as well as the bottom of the stretcher, is the first plane of reference for the dowels. The inside face of the stretcher and the inside face of the leg are the second. Lay out and drill the dowel holes.
• With the holes drilled, chamfer the edges of the stretchers and the back slats on the router table.
• Dry assemble the slats and rails together using dowels, and if everything fits, sand all of the parts for finishing and apply a coat of tung oil. When the finish has cured, glue up the rear panel. Be sure to check the diagonals for square.
• The two decks (ie. the upper work surface and lower storage shelf) are where this project either comes together or falls apart. The upper deck is glued together forming a rigid platform with gaps between each board. The lower shelf is made of loose boards laid edge-to-edge to form a solid surface that things won’t fall through. With so many boards laid side-by-side, there is the potential for considerable seasonal expansion. Failing to allow for an expansion joint would force the bottom shelf to act as a ram and pry the joints with the ends apart. On the rigid upper deck, there is space between each board for expansion and the two dowels in each end are oriented along the length to prevent the board from splitting.
• Mill the material for the four shelf runners (F) and cut them to length.
• Mill the material for the lower shelf boards (G) and cut them to length.
• Mill the material for the top boards (H) and cut them to length.
• For the following stages you will have to begin assembling the potting bench. Assemble the sides, back panel, and front stretchers. Take two of the shelf runners and set them into the notches in the lower side stretchers. Use a couple of band clamps around the legs to keep the whole assembly drawn tight, or you will be unable to accurately locate the dowel holes for the runners.
• Set the upper shelf runners into the notches in the upper stretcher. The runners should run to the edge of the chamfer on each leg. Use some form of a clamping jig to ensure the bench is standing square. I used a 12″ melamine square with some 2 ½” clamp holes drilled into it.
• The slats for the upper deck will overhang the front, back and sides by ½” with a ¼” space between each slat. To be sure that everything aligns, it is important to establish the same reference edge for all of the dowel holes. Place one of the top boards in place and establish the proper overhang on the front and back. Transfer the location of the front edge of the two.
• Find the center of the shelf runner end to end. Working out from there, use a square to draw lines out in either direction on 3 ¾” centers. This represents the centerline of the two dowels in the runners. They are simply centered on the individual boards.
• Drill these holes to a depth of just slightly more than ⅜”. In all likelihood you will not find any ⅜” x ¾” dowels so simply cut some 1 ½” dowels in half.
• Test fit the top boards to the runners.
An Expanding Bottom
• Set the boards for the lower shelf in place. They will be too wide for the space available so leave the last one out and a gap in the middle.
• Use a table saw or jointer to slightly bevel the edges of the two boards facing each other over the gap; 10º should be more than enough.
• Bevel one edge of the remaining board originally left out. Use the table saw set at an angle to rip the piece to width to fit in the gap, then drop it in place. With the edges on either side of the narrow center strip bevelled, any seasonal expansion will cause the center strip to buckle upward and pop out, preventing the leg to front and rear stretcher joint from being forced open.
• With the fit confirmed for the two shelves, remove the boards and runners.
• On a router table, chamfer the edges and ends of the top boards.
• Sand all of the parts and apply tung oil to all of the pieces. Leave an area around the dowel holes on the upper assembly free of finish. This will provide additional surface area for the glue (that squeezes out of the dowel holes) to adhere to.
• Place the upper runners back in the potting bench, insert the dowels and place the top boards in place. Start at one end and remove each board individually, apply glue and press it in place. Be sure not to accidentally glue the runners or boards to the bench!
Tie It All Together
• When the glued top assembly has cured, remove the top and set it aside. Use a guide to drill a 1″ deep hole in the center of each of the four notches the runners sit in.
• Place a dowel center in each of these holes and carefully center the top on the bench. When the top is centered, press down on the four centers to mark the location in the underside of the runners. Drill this to a depth of ½”.
• Place a dowel in each notch and set the top assembly in place.
• Repeat this for the two bottom runners as well and insert a dowel in each notch and place the runners over the dowels. This will hold the potting bench together at this point and you can remove the band clamps.
Top It Off
• To create a little extra storage space for seeds, tools and pots, or condiments and other accoutrements next to the BBQ, add a simple hutch to the top. If you can find some wide stock then make each piece from a single board. If wide stock is not readily available in your area, glue up some narrower stock using type 2 wood glue, such as Titebond III.
• Mill the material for the five hutch components (I, J, K, L) and cut them to length.
• Lay out and drill dowel holes to join the shelf to the back. Assemble these two pieces without glue for the next step.
• Lay the sides on a table and place the assembled shelf and back in place between them. Line up the top edge of the back and the top edge of the sides. Mark the underside of the shelf on either side. Measure back ⅜” to locate the centerline of the dowels. Drill the holes in the ends of the shelf, back and in the sides.
• Lay out and drill the dowel holes for the top and dry fit everything.
• Disassemble the pieces and chamfer the visible edges on the router table, sand and finish each piece.
• Glue the hutch together and clamp it. Check the diagonals for square.
To Glue Or Not To Glue
• At this point the legs to front and back stretcher joints have not been glued. As well, the eight dowels that hold the four shelf runners in place are not glued. This is where the knock down aspect mentioned earlier comes in. If you have drilled these holes accurately, the front and rear stretchers will keep the ends apart, while the dowels in the shelf runners keep the two ends together, effectively locking everything in place. Cedar is a soft wood and I would recommend making the shelf runners and the upper end stretchers out of a harder wood (teak or white oak would do nicely) or the holes will become worn quickly and your bench will rock side to side. For a permanent version simply glue these dowels in place and the bench will become perfectly rigid.
• Place the hutch on top of your finished bench and you’re ready to start your seedlings for the garden.
Get Your Holes In A Row
To make dowels work in a project you have to be able to easily and accurately drill holes precisely where you need them. Over the years I’ve built plenty of dowel jigs for various situations, investing considerable time I would rather have spent working on my projects.
I recently picked up a DowelMax at the Victoria wood show, after watching a demonstration by it’s designer, Jim Lindsay. The heart of the jig is a precisely machined aluminium guide block with 5 hardened drill guides for either ⅜” or ¼” dowels. Using a combination of the fence, angle bracket and the clamp bracket with the guide block it is easy to locate the jig anywhere on the work piece. By always using the same two reference faces, drilling perfectly matched holes in facing pieces that match up every time is child’s play.
A guide rod allows perfect spacing of holes on longer surfaces while drop in spacers center the jig on stock of different thicknesses. The bit included with the kit drills a perfectly sized hole for Laurier dowels.
A tool is only worth investing in if the return is worth it; it has to be cost effective, and with DowelMax commanding a premium price it has a lot to live up to. It’s easy to assume that a tool like this is made by a huge company and that the price is unreasonably high. Consider that in this day of most tools being made in China, Dowelmax is a small family run business based in
North Vancouver. There are over thirty components in the complete system, that are all made at three local independent machine shops out of the highest quality materials providing employment for several skilled craftsmen.
So does the DowelMax live up to the promise, and is it cost effective? In a word, absolutely. All 384 dowel holes in this project lined up as if they had been drilled using a CNC machine. Given the precision and ease of use of the DowelMax I plan on using it for a lot more projects.
Successful Dowel Gluing
There are three things that make a dowel joint come together perfectly. If any of the three are not right, the joint can be frustrating to assemble.
First, you need the right dowel. I’ve experimented with different glues and different dowels. Some work, others leave a lot to be desired. The dowels made by Laurier Woodcraft (available through Lee Valley) are superior to any I have tried. These have spiral flutes and are slightly compressed, but more importantly, they are round. All other dowels I have tried have been out of round enough to result in a sloppy or difficult assembly. Laurier dowels provide a tight solid fit that can be easily assembled by hand and in the presence of glue they expand just enough to lock the joint tight.
Second, you need the right glue. Dowels expand as they absorb water from the glue and choosing the right glue is critical for a successful joint. Normal carpenters glue will set up far too fast and lock the dowel in place before the joint is fully assembled. To allow extra working time, use a product with a longer open time. I like Titebond III which allows ample time to get the dowels in place and assemble the joint.
Third, you need to accurately drill the holes. See sidebar ‘Get Your Holes in a Row’ for more on this topic.