Few woodworking tasks are more frustrating than gluing up and clamping a large, flat panel. For hassle-free tabletops the rest of your woodworking life, invest a few hours in building this nifty jig.
When my wife announced recently that she wanted a new coffee table, I began thinking about the best way to glue up a really flat panel for the top. This can be a harrowing experience. Positioning clamps under and over the boards simultaneously while trying to tighten them before the glue begins to set … well, it just makes your heart pump! I’ve read many solutions for this, and even tried a few. It seems, though, that I always end up running a hand plane across the surface of my panels, then a belt sander and finally a random orbit sander, just to get the surface flat. Then, of course, I have to flip the panel and go through the same procedure on the other side. In the end, I get a great workout — and a nice panel that’s always a bit thinner than planned.
So, I went through my collection of woodworking magazines, searching for the one method that might deliver reliable results — a panel that is flat enough not to require a whole lot of sanding and planing.
I use ¾" pipe clamps in the shop. They’re not exceptionally stable when sitting on a bench, tending to slide around and tip over. And they’re never all the same height, because I’ve collected them over the years so they represent several manufacturers and models. I decided to build a jig that would cradle the pipe clamps, holding them steady and keeping them all in the same horizontal plane. The jig would allow access under and over the panel, so I can use cauls (more on these later). The final result resembles a ladder and has very few major parts: a couple of 1x6 cradles to hold the pipe clamps and provide equal distance between them, and five 2x4 braces to hold the cradles on edge. Under the braces, I added some 2x4 risers, to separate the jig from my workbench, and some spacers to help line up the clamps. The ¾" pipes, rather than the clamp heads or tails, are the only things that touch the jig, so now my clamps are always in the same horizontal plane.
Milling the parts
You could build all of the jig in high-end hardwood, but I decided to spend around $20 at the local home improvement center on good quality 2x4 lumber for the braces and risers, and a piece of ¾" poplar for the cradles. You just need to make sure that your lumber is machined straight and square. The jig is made for a flat panel that starts life at 24" wide and 60" long. It will work for panels as short as 16" long and less than 24" wide, and you can modify the dimensions to build a jig for almost any size panel.
From one 2x4, cut three pieces that are 26" long (Fig. 1). I used a stop clamped to the table saw fence and my miter gauge to do this (Fig. 2). Cut two 26" pieces and a 23" piece from another 2x4. Then cut four 23" lengths from the third 2x4. The 26"-long boards will be the braces, while the 23" boards will become cauls later on. Save the two cutoffs from the first two boards. These will become the risers and test-cut pieces.
Joint one edge and one face on each piece (Fig. 3). Then plane them all to a consistent thickness and width (Fig. 4). (You could trim them to width on a table saw, but it’s just as easy to run them through the planer.) Crosscut the ends square and trim them to their final lengths.
Now you’re ready for the long 1x6 board that will become the two cradles. Joint one edge and a face, then clean the other face by running the board through your planer. Cut two lengths of 63" and save the short cutoff. This will be used later to make some short spacers.
It’s time to cut some dadoes. Each brace needs to have a dado cut near each end, into which the cradles are inserted. Here, my choice of weapon was the table saw, and I opted to use a dado head because the width of cut is infinitely variable. This allowed me to make extremely accurate cuts so the cradles were actually a friction fit; no glue was necessary to hold the jig together. A friction fit also makes it easy to disassemble the jig after use; it takes up a lot of storage space when assembled. If you intend to use the jig often, it’s best to use a little glue and a couple of brads on each base brace to keep the jig aligned.
To cut the dadoes, I attached a long sacrificial scrap wood fence to my miter gauge and clamped a ¾" stop to my fence. The dadoes should be cut 1½" in from each end. Adjust your blade to the thickness of the 1x6 that you planed, set it to make a ¾"-deep cut, and mill all 10 dadoes. Stay with the table saw and switch back to a crosscut blade. From one of the leftover pieces of 2x4 (that were also jointed and planed), cut 10 pieces 3" long. These are the risers that will be glued to the bottom of each brace.
Assemble the jig
On the bottom side of each base brace, mark a line 4½" from each end and attach the risers (Fig. 5). The inset is designed to leave room for a bar clamp head to fit under each end of the braces (more on this in a bit). Hot melt glue works great for attaching the riser blocks. All the pressure on this jig is downward, so there should be no movement in the risers. But, if this is a jig you intend to use over and over, wood glue and clamps make a more permanent bond.
It’s time to turn your attention back to the cradles now. The 1x6 is already jointed and flat. Find and mark the center of the board (at 31½"). Now mark 14" and 28" from the center in both directions. These are the clamp locations, 14" apart. Use a square to draw a line across the width of the board at all five marks (Fig. 6). This line serves not only as a mark for drilling holes, but also to line up the cradles with the braces during final assembly.
Set up a fence on your drill press and chuck in a 11/8" Forstner bit. The fence should be adjusted so that the center of the bit is 2½" from the jointed edge of a 1x6. I attached hold-down clamps to my fence to keep the board rock steady while drilling (Fig. 7), and added a ¾" board on top of my drill press table under the workpiece, since I’d be drilling through holes. Now drill one hole through the board at each of the five locations. Return to the table saw to split the 1x6 lengthwise into two pieces, each just less than 2½" wide (Fig. 8). Run the offcut piece through the saw with the drilled side toward the fence. This creates two boards exactly the same width.
From the leftover piece of 1x6, rip a couple of lengths that are 11/8" wide. Then cut 2¼" long pieces from these lengths. These are spacers that will be glued to the jig, to help align the pipe clamps. On the top side of each brace (the side with the dado cuts), measure the width of each piece and mark it halfway across. Draw a line from each dado to the end of the brace, halfway across its width. This will meet the line you drew earlier on each cradle (Fig. 9), to ensure that your jig is square.
Lay the two end braces on a flat surface with access on all four sides. (I have two benches; one is littered with bench-top tools, the other is against a wall. So, I use my table saw as my flat surface!)
Line up the mark on one cradle with the line on one of the end braces and begin pressing the cradle into the dado cut. Then press the cradle into the other end brace, making sure the lines on the cradle and the base line up. My fit between the dado and the cradle was so tight I had to use clamps to force the two together. Continue pressing the first cradle into the remaining three braces, again making sure the lines line up. Then go around to the other side and press the second cradle into each brace, making sure that they are lined up properly. Add the spacers along one side of the jig. Hot melt glue again works well here (Fig. 10). The spacers are 11/8" tall which will position their tops about 1/16" beneath each half hole in the cradle. In use, snug your clamps up against the spacers; they will position the clamps in a straight line, and distance the clamp heads from the cradle.
Using the jig
In use, I cover my table saw with a poly sheet to keep glue off the surface. I also clamp the jig to the table at both ends, to make sure it doesn’t slide around while I’m frantically gluing and clamping boards together. The jig is designed to glue up a flat panel in its finished thickness. So, joint and plane your boards to the thickness you’ll need in the end. There will only be a little cleanup and some light sanding after the glue dries.
Set your clamps in the jig and space the head and tail about an inch further apart than the combined width of the boards to be glued up. Run masking tape along the top of the pipes to prevent any transfer of color from the pipes to the boards.
Cauls are just pieces of wood that force the middle of the panel flat against the clamp bars. As the edges of the panel components are being forced together after gluing, the cauls are laid on top and clamped in place (Fig. 11). There are a few solutions to keep the cauls from being glued to the boards; one is to put several coats of polyurethane on them (very time-consuming). Another is to wrap waxed paper around one edge and tape it to each face of the cauls (also time-consuming). My personal preference is to run 2"-wide packing tape along one edge, and then fold it up onto each face (quick and easy!).
Place the boards in order on the clamps and start applying glue. Run the head of the center pipe clamp in until there’s just resistance and a little glue starts to squeeze out. Place a caul (with its taped side down) across the boards, right above the pipe clamp. Put a clamp under the brace and over the caul, and tighten it. Then go around to the back and do the same. Now gently tighten all of the pipe clamps, working out from the center. Don’t put too much pressure on the clamps yet; just tighten them to the point of a little resistance. Place the remaining cauls over the other four pipe clamps and clamp each in position. Now go back to the center pipe clamp and tighten it. Work your way out from the center clamp in each direction, tightening as you go.
After the glue dries, remove the panel and scrape off the squeeze-out. Run a random orbit sander over both sides. And now you’ve got a large panel that you don’t need to run through an industrial-sized planer or a wide belt sander. Your panel is flat and ready to be trimmed to size.
Jon T. Hutchinson
Jon T. Hutchinson is the editor/associate publisher of Markee Magazine, a trade publication for and about the U.S. film and video industry. He’s been an avid woodworker and furniture designer for 30 years, at times for profit, but always for the love of the craft. He and his wife live in Deland, Fla.
Tools used in this project
Table saw, jointer, planer, drill press, hot glue gun, clamps
