The concept behind edge-gluing boards to make wider panels is very simple; all you have to do is apply glue to the edges of a series of boards, clamp them together and wait for the glue to set. That sounds easy enough, and in a perfect world it would be. Unfortunately, most of us haven't been able to locate that woodworking utopia where everything just seems to work right all the time. Living in the real world doesn't mean that you can't create stunning projects in your shop, it just means that you have to work at it a little. Lowe's is happy to provide this information as a service to you.
Match the grain patterns on the facesof your boards so that each board flows naturally into the next. Taking the time to match the grain patterns makes the glue-up look more like one large board and gives your entire project a more aesthetically pleasing look.
The red line indicates the "glue step" on these boards.
Your boards should have approximately the same grain pattern when viewed from their ends. The end grain pattern indicates the amount of wood movement each board is subject to across its thickness (from face to face). Boards with dissimilar end grain patterns shrink and swell at different rates, causing the panel to warp or twist. In extreme cases, the pressures of wood movement can cause the glue joint to fail. Another defect that can result from using dissimilarly end-grained boards is called glue step. Plain sawn boards shrink and swell less from face to face than quartersawn boards, and these two distinctly different types of boards should never be used in the same panel for a glue-up.
Moisture content (MC) is another important factor when matching boards. Eventually all of the boards in a panel will acclimate to their surroundings and reach the same MC (within roughly 1/2%). To ensure that your boards are at the same MC air stack your lumber and let it acclimate in the shop for at least a week before working with it.
When you lay out the boards you also need to note the end grain pattern of boards adjacent to one another. There are at least three schools of thought as to which is the best way to arrange your boards:
Either layout method can work or fail equally well. In years past, before air conditioning and central heating, the alternating technique was the standard and it worked well in a home with wildly changing humidity and temperature. Alternating grain layout is still a good idea for pieces that will be exposed to the elements. But, if your project will be in an environment where the temperature and humidity will be relatively constant, and you have acclimated your stock to that temperature and humidity, any of the methods above should work for your glue-ups.
Note that end grain pattern isn't as much of a concern when you are gluing quartersawn boards, since the growth rings run generally perpendicular to the board edges.
Straight, square boards are essential for successful glue-ups. The edges and faces of the boards must be perpendicular to one another, and the boards must be free of crooks, checks and twists. Even if you use presurfaced lumber, it's a good idea to check for small imperfections that may have occurred after the boards were milled. Correct slight crooks by jointing the boards on a jointer or ripping them on a table saw, cut off checks, and don't bother with trying to use twisted boards all.
Cut the stock 2" or so longer than the final length you need for the finished panel, and plan to make the original glue up 1" wider than the desired width of the panel. Making the initial glue-up slightly larger than the desired final dimensions gives you the opportunity to cut off any uneven ends that may result from boards shifting as you clamp the panel. It also gives you the ability to remove stock from the edges of the panel that may be dented from excessive clamping pressure.
The triangle serves to register each board's position in the panel.
Lay the boards out with in the same order you intend to glue them. Make a final check of all the joints to ensure the edges meet evenly, without gaps. Remachine as needed. Also check to see that the faces of the boards are in the same plane. If you have any board faces that stand proud of the others, plane or sand the board/s to match the thickness of the rest of your stock. Once you are satisfied with the dry fit, use a soft lead pencil to lightly draw a triangle across the panels. The triangle serves to register each board's position in the panel and makes it easier to assemble the panel during the final gluing process.
When first applied to the edges of the boards, the glue will act more like oil than adhesive (this is called glue slip). The boards will slip and slide against each other as you apply clamping pressure. To overcome glue slip you can use dowels or biscuits in the edges of the boards to keep them in place. Just be sure to follow the instructions with your doweling jig or biscuit joiner and dry fit the pieces again to be sure the boards still come together correctly. Another way to defeat glue slip is with wood cauls. Cauls are simply straight pieces of lumber that are clamped to each end of the glue-up. The cauls provide enough friction on the faces of the boards to keep them from sliding. They also stop the panel from bowing that is sometimes caused by clamping pressure. Use wax paper or cellophane tape between the cauls and the panel to keep glue squeeze-out from adhering the cauls to the panel.
Some wood species have natural oils that inhibit the glue from penetrating the wood surface and creating a good bond. It is a good idea to wipe the gluing surfaces of the boards with acetone to remove any oils and clean the surface.
The clamped panel.
Secure the clamps on your worktable with the jaws facing up. Open the jaws so they are several inches wider than the panel will be. Place wax paper or cellophane tape over the clamp bars. Place clamping blocks across the clamp bars abutting the jaws. The clamp blocks will keep the jaws from denting the outside boards in the panel. Lay out the boards on the clamp bars and brush a light coat of glue onto each mating surface. Align the boards (if you are using cauls, add them at this time) and clamp them in place. Be careful not to overclamp the panel. Excessive pressure will force too much glue out of the joint and weaken the panel. You can either wipe the panel with thinner for the glue to remove the squeeze out while it is still wet or wait for the glue to harden and remove it with a scraper.
Allow the assembly to set according to the glue manufacturer's instruction. Unclamp the panel and set it aside to finish curing before trimming it to size.