Ever wondered if gluing those pocket hole joints is worth the extra effort? You’re about to discover the ‘how’ and the ‘why’ behind using glue in these joints.
Yes, you should glue pocket hole joints. Gluing enhances joint strength, prevents separation due to wood movement, and is ideal except in cases where disassembly is needed.
Pocket Hole Joinery
We know the history of pocket hole joinery and have written of it in past articles, including:
- Attaching table legs to a table apron using pocket hole joinery
- Screw sizes for pocket holes and
- Pocket hole joinery strength for shelving
Most recently, we wrote about using pocket hole joinery on mitered corners.
Pocket hole joints go back to Craig Sommerfeld and his wife circa 1989. Craig was building new cabinets for their kitchen, and his wife asked him to hide the screw holes from view. To oblige her, he developed the concept of pocket holes as a way of joining two pieces of wood and built the first pocket hole jig.
It succeeded beyond his expectations, and he kept building them for sale at woodcraft shows. Sales and demand grew, he built more and more of them, and in 1990 applied for and was awarded a patent for the Kreg jig.
Sales were boosted by a 1995 cover feature story in Wood Magazine, and in 2003 Lowe’s began carrying the jig and other products manufactured by Kreg in all of their stores across the country.
It is the standard by which all pocket joinery jigs are measured, and it’s a great story. You can pick up a single pocket hole jig for around $15 and around $140 for a 3-hole jig. You can even purchase a pocket hole machine for around $400.
Save for the $400 pocket hole machine; the price points are not so high you can’t afford to have a couple of them in your woodworking shop. If, for instance, you are using pocket holes to edge join planks for a tabletop, having a few of them to use along the spans will speed up the process for you.
Pocket Hole Screws
Kreg also makes pocket hole screws for use with its jigs and pocket hole drill bits. The pocket hole screws you use will depend on the wood you are using, and the size of the pocket hole screws will depend on the size of the pieces of wood being joined. There are two types of screws:
- Coarse-thread screws for use with softwoods, as their threads are deep and aggressively grip the wood; and,
- Fine-thread screws for use with hardwoods, as their threads will not tear the wood fibers.
Sizes range from 1” to 2 ½ “, and the size you choose to work with depends on the depth of the pocket hole you are drilling in the first piece of wood.
The pocket hole screws have a square drive to provide greater torque. The flat bottom of the counterbore will act as a good stop when the screw has reached its end point. The pilot hole drilled by the drill bit will guide the screw exactly where it needs to be as it enters the second piece of wood being joined.
Kreg pocket hole jigs come with a handy chart that identifies the size of the screw you should use for whichever dimensional wood you are using in your project. Most of the thinking is taken out of the task with such advice, and if you follow the chart, your joinery will likely be exactly what you need.
The Pocket Hole Drill Bits
The pocket hole drill bit is designed specifically for the joinery task. It’s stepped in shape and size and has a short and narrow-width pilot hole point at the tip. As mentioned above, it has a flat-bottomed counterbore shaft to accommodate the head of the screw.
The pocket hole screws are hardened and self-tapping with its wide washer head, and the screw threads are long and deep. The drill bit creates the perfect angled hole through which the screw passes so that it can grip the second piece of wood strongly to the first and form that solid joint.
The pocket hole drill bit has a stop collar that adjusts to your settings (again, follow the chart here) to make sure the hole you drill is to the right depth for the word and the screw being used.
Wood Glue Types and Uses
We, woodworkers, know there are three basic types of wood glue available for use in our shop:
- PVA, or polyvinyl acetate, commonly referred to as wood glue, the most famous of which is Elmer’s and the white glue we regularly use;
- Polyurethane, most commonly called Gorilla glue because that was the first company to introduce it to the US market; and,
- Aliphatic, a synthetic resin glue of which Titebond is the most familiar brand, is a synthetic adhesive known for its yellow color and creamy consistency.
Wood glues generally are designed to penetrate the wood fiber to create a deep bond that will actually be stronger than the wood itself – the strength of the wood plus the strength of the glue. Glued joints, even if there are mechanical items used (nails, screws, brads), are simply stronger because of the glue.
Wood glue is likely in every woodworking shop, or at least it should be. It’s easy to use, quick to dry, and easy to clean up after when you’re done. We use glue in all of our joinery.
Glue and Pocket Hole Joints
Now that we know what pocket hole joinery is, and have the basics down about the use of glue in joints, let’s consider whether they work well together or even whether they should be together.
The question we would ask is, why wouldn’t you use glue with pocket holes? Could it hurt the joint? Would it weaken the work being done by the pocket hole screws?
Using glue with pocket hole joinery will keep the joints from opening up. Over time, wood shifts and moves about. Glue will certainly hold wood pieces together and prevent shift and misalignment. Glue will step in and keep the joint tight even if, over time, the screws in a pocket hole joint relax their grip.
Even if you’ve made sure the wood you are using is fully cured and will not likely warp, wood is affected by seasonal changes. Glue will help thwart that seasonal separation.
If your project is what you consider to be a high-end project, one that might include the use of pocket hole plugs to hide the head of the screws, you’re going to be using glue for those plugs. If you are going to be gluing anyway (the plugs), you might as well go the full distance and glue the joint, too.
All of that, having been said, there may be times when you would not want to use glue with pocket hole joints. They include:
- Anything you might want to take apart later. For example, kitchen or workshop cabinets. You may not want to use glue during installation of the center stile in a cabinet face frame – perhaps you will want to remove the stile for unencumbered access to the cabinet chamber. Or, you’re moving and want to take that custom shelving unit with you. It might be easier and/or safer to take the unit apart before moving it, and glue would just get in the way of that disassembly.
- Really simple projects. For instance, maybe you need to build a few simple boxes for light storage in your shop or office where strength is not an issue. In those types of projects, glue isn’t absolutely essential.
As for the process, it’s simply common sense. Glue first, and clamp the two pieces in place together before you drive the pocket hole screws. Then simply wait for the glue to dry, and your joinery is done, the joint formed, and you have the added measure of strength from gluing.
It’s not quite a “belt and suspenders” concept, but it isn’t that far from it, either. The few seconds it will take to apply the glue is well worth it, and as you know, wood glue is not expensive, and you likely already have it in your shop.
In answer to the specific question “Should you glue pocket hole joints,” we’ll answer with the question we asked earlier: Why wouldn’t you, except in those instances we’ve cited? It won’t hurt the joint, and it will add a measure of strength to it. If you’re using pocket hole plugs (with glue), it’s not a stretch to use the glue to form the joint, too.
We found support for our conclusion in a video from the Woodworkers Guild of America. It’s a short video with explanations, and it’s worth a look.
You’ve got the glue, you’ve got the jig, you’ve got the drill bit, and the screws. It won’t harm the joint, and in fact, it will help. Other than instances where you might be taking the joint apart, as examples cited above, glue is a good idea.
Glue it up, use clamps to hold everything in place, and be patient enough to let the glue dry, and you’ll have an extremely strong joint. Isn’t that the point of the exercise?