Sometimes things can be so good and useful that we just keep returning to them. Tomato soup and grilled cheese for lunch, or that old bathrobe we just can’t toss away, for instance.
In woodworking, we keep turning to pocket hole joinery for the same reasons. It just works. It’s quick and easy, and it’s very strong. And we like it. We’ve written about it from various angles and projects in the past, most recently here.
Pocket hole joints can join 2 pieces of wood in just about any way you need, whether edge to edge, edge to face, and even mitered. Pocket hole joints are very common in structural frames and cabinet face frames.
Their strength is superior to that of mortise and tenon joints, dowel joinery, and biscuit joinery, in such uses. Now, cabinet face frames are not carrying weight, and that distinguishes them from other joinery purposes. In fact, when Craig Sommerfield invented the Kreg Pocket Hole Jig, it was to please his wife who had asked that no screw holes show in their new cabinets.
But, structural frames should give you a clue to the answer of the main question. We’ll get to that in a little bit. First thing’s first.
What is Pocket Hole Joinery?
Pocket hole joinery involves the drilling of holes in one of the pieces of wood to be joined, stopping short of the edge, and then using screws through those holes through the edge and into the other piece of wood being joined. The holes are drilled at an angle, and the screws extend at least half-way into the second piece of wood, creating a strong and durable joint.
It is common in frames (picture, painting, etc.) and joining a plate to the underside of tables and table legs, as well as the aforementioned cabinet face frames. A jig makes the drilling easy and quick, and perfectly aligned, and Kreg, the premiere pocket hole jig manufacturer, even manufactures screws to be used for the joinery.
Pocket hole screws come in various sizes and two main types, the use of which is determined by the woods being joined:
- Coarse-thread screws should be used with softwoods, as the threads are deep and aggressive in their grip; and,
- Fine-thread screws should be used with hardwoods, as they will not tear the fibers and lead to splits.
The jig also makes it easy to drill repetitively and accurately along the span of lumber for more extensive joinery. Once the right depth of drilling has been determined and the depth guide has been set, you just move along the span with your drill. Screwing becomes that easy repetitive process, too, once you’ve changed the bit of the drill.
The length of the pocket screws is determined by the dimensions of the bottom board. As a general rule, the screw should reach at least half of its thickness. And, as you can now see, the depth of the drill hole determines the length of the pocket screws.
How Strong Are Pocket Hole Screws?
In our previous article on pocket hole screws, we reported a strength test that suggested a pocket screw joint failed at 707 lbs when subjected to shear load, while a mortise and tenon joint failed at 453 lbs.
In another test we found, a common 90-degree pocket hole joint that used a 2 x 4 rail attached to a 4 x 4 post was able to support a load of 1391 lbs before it failed. That’s more than 8 times what I weigh, so 7 of me could have stood on that rail with it collapsing. Fairly impressive.
For a more durable and stronger joint, perhaps you’d want to turn to lags and carriage bolts, or even Simpson brackets, but those are a story for another article. Think a large bed frame that must carry both weight and activity.
For those projects that customarily involve pocket hole joinery, though – cabinets, picture and art frames, dining room tables, and such – the use of pocket hole screws will be more than adequate.
One other subject worthy of note is the use of glue with pocket hole joinery. As we mentioned in previous articles, it’s never a bad idea to use wood glue in joinery. The added strength certainly won’t hurt, and if the project is a piece that will be used often and experience a bit of wiggle and jostling, like a dining room table, the use of glue will be a good addition to the joint.
Pocket Hole Joinery and Shelves
We know that pocket hole joinery is easy, quick, and strong. Of course, the wood you are using, and the dimensions of it, will have an effect on that strength. But, generally speaking, it’s a strong and durable method of joining 2 pieces of wood.
The shear tests we mentioned earlier suggest the extent of that strength, too. With 707 lbs before failure, and 1391 lbs before failure, we know what can be done with pocket hole joinery.
We know that pocket hole joinery is the first choice for cabinet makers – frames, face frames as we mentioned earlier, and carcasses, and for such projects as stairs (the tight joint of tread to riser eliminates squeaking better than the odd nail), and edging along kitchen countertops and at your dining room table.
These uses of pocket hole joinery are obvious, and the benefits clear. They hold things together tightly, eliminate wobble and squeak (that sounds like a British food dish), and remove the holes from view. Things get held together well and truly, and will remain so for a long time.
This having been said, why wouldn’t pocket holes be strong enough for shelves? The considerations would be several:
- The wood you have chosen to work with
- The purpose of the shelves
- What the shelves will be holding or storing
- How many shelves will be in the case
Each of these considerations will determine the depth of the drill hole and the length of the screw you will use in each of the pocket holes.
But, for a shelving project, a pocket hole is an excellent choice for the joinery of shelves to frames.
Kreg pocket hole jigs come with a wealth of information and suggestions for the woodworker. Among all of the information are such details as:
- the depth of holes depending on the stock you are using;
- the length of screws recommended for that stock; and,
- the spacing of the pocket holes to be drilled along a span so as to provide maximum strength to the joinery.
A single pocket hole should be avoided and another method of joinery should be considered when possible. You wouldn’t want a shelf to spin, for instance, with the screw as the center of the spin. As unlikely as that is to happen, it’s still wise to use more than one pocket hole in shelving or anything else.
Finishing a Pocket Hole Joint To Hide The Hole
Mrs. Sommerfield asked her husband to hide the screw holes in their new cabinets, and he came up with the jig. The pocket holes in cabinets can be seen, but they are inside the cabinets where no one looks.
When joining shelving to frames, the pocket holes are underneath the shelves, and depending on how high the shelving is, the holes could be seen. However, this is where pocket hole plugs come in.
Yes, you can buy a bag of pocket hole plugs to fill those holes up. A little glue, a gentle persuasion into the hole, and you’re done. Sand them down to surface smoothness, and they add an attractive finish to the joinery.
Floating Shelf with Pocket Hole Joinery
You might be wondering about using pocket hole joinery with a floating shelf. Wonder no more, as this is also a good project for pocket holes. Rather than walk you through it with words, we found a good video that will do that for you.
How Much Weight Can Pocket Hole Shelves Hold?
The two tests we mentioned suggested 707 lbs and 1391 lbs with the wood and the joint of each identified.
Books don’t weigh anything close to that, and the length of a shelf that could hold 700 lbs of books would be extremely long and be supported from beneath along the span. It’s not likely you’re building that large a shelf in your home workshop.
But, books are not the only items that shelves are used for storage and presentation. Shelves in your kitchen might hold your pots and pans, or a countertop mixer. In these instances, you will have chosen a wood or plywood suitable to bear that kind of weight, and if the wood is strong enough for that intended use, a pocket hole joinery that uses the right depth, screw length and type of screw will support your kitchen “stuff.”
Choosing the right materials and the shelving length and any support along the shelf span as necessary will determine how much weight your shelves can bear. The pocket hole joinery will be secondary to those calculations.
Books, knickknacks, framed pictures, pots and pans, countertop appliances in your kitchen, are all common items on shelves. None of them are going to come close to what the weight testing shows pocket hole joints are capable of supporting.
Here’s an entire shelving project using pocket holes. It shows assembly with pocket holes, as well as the use of pocket hole plugs. It’s worth watching.
Choose your materials wisely, map out the span strength of the shelves, and follow Kreg’s recommendations on hole depth and screw length. Pocket hole joinery will serve you well with your shelving project.
