We like pocket hole joinery. A lot. And we use it often in our own shop for many woodworking projects. Pocket hole joints are solid and strong, and they hold well and tightly for a long time. We’ve written about it in past pieces, most recently here and here.
Pocket hole joints can be used to connect 2 pieces of wood as you wish – edge to edge, edge to face, and mitered. They are commonly used in structural framing and cabinet face frames.
In this type of joinery, holes are drilled in one piece of wood that stops just short of the edge of the piece. Screws are then used through those holes and into the second piece of wood. The angles of the holes and the correct choice of screw length will get it at least halfway through that second piece of wood, thus creating a strong and durable joint.
The correct choice of screw type and size is an important aspect of pocket hole joinery, and impacts on the answer to the main question of this article. We’ll get to that in a moment, and offer several tips we’ve learned from other woodworkers and from our own experience.
Pocket Hole Screws
There are two main types of screws used in pocket hole joinery:
- Coarse-thread, used with softwoods to give a strong grip; and,
- Fine-thread, used with hardwoods so the wood fibers are not split or ripped.
In addition to these two main types, screws also come in a variety of sizes and heads. Among the head styles is the pan head.
Pan head screws are a common head type of non-countersunk screws used in making woodworking screws, self-tapping screws, and self-drilling screws. They are characterized by wide and flat heads, usually curved sides, and recessed sockets. They present a low profile once sunk, and that can be an important consideration when joining plywood.
They differ with their flat heads from round head screws that have a larger profile and a domed head. That round, domed head creates a half-sphere that sits higher on the screw than the flat surface of a pan head. If you intend to use plugs to hide your pocket hole, this can be a concern.
The significance of this will become apparent shortly, and we’ll address it in our tips when joining plywood.
Pocket Hole Jigs
As we all know, jigs take a lot of the thinking out of the equation in woodworking projects. This is especially so in joinery. The first name in jigs for pocket hole joints, of course, is Kreg. If you’ve read any of our previous articles on pocket hole joinery, you’ve seen Kreg mentioned prominently.
Craig Sommerfeld invented the pocket hole jig in the late 1980s to satisfy his wife’s request that the screws holding the new kitchen cabinets he was building for their home be hidden from view. He devised the pocket hole concept, built the first jig, made his wife happy, and began selling them at woodcraft shows.
Successful sales led to increased production, and a patent was issued for the Kreg Jig in 1990. In 1995, a cover feature story in Wood Magazine then helped jig sales take off. More products were designed and offered for sale, and in 2003, Lowe’s began carrying Kreg products in all of their stores across America.
In the fall of 2021, Kreg moved into a new global headquarters in Ankeny, Iowa, that provides the necessary space for it to meet global demands for its products.
Kreg jigs come in several configurations, and the jig you choose for your woodworking shop will depend on the projects you are likely to pursue. However, the jigs are not so expensive that you couldn’t carry a couple of them in your tool inventory.
A single hole jig can be found for around $20, and a 2-hole jig not much more at around $32. Smart shoppers who compare vendors and shop for sales can save a few dollars off those prices, even. They are available at local hardware stores, big DIY stores, and online retailers.
Plywood and Pocket Hole Joinery
Plywood is a manufactured product of thin veneers joined together with glue. The grains of the veneers are rotated up to 90 degrees to one another to enhance the strength of the sheets.
The rotation of veneers in the manufacturing process serves 3 main purposes;
- It reduces the tendency of the sheet to split when it is nailed at the edges and corners; and,
- It reduces expansion and contraction of the sheets; and,
- It makes the strength of the sheet consistent across all directions.
There are 3 main types of plywood, too:
Sanded. Face and back sides are sanded in the manufacturing process and is used in applications where it will be seen, like cabinets, shelving, and paneling.
Hardwood. Made from – you guessed it – hardwoods, like birch and oak. The veneers or plies (thus, plywood) are glued at right angles to each other and are very strong and stable. These are used in furniture making and where load-bearing strength is required.
Structural. Used in constructing permanent structures. It’s inexpensive and strong but is unfinished. It’s commonly used in framing and flooring, places where it will not be seen.
Within these types, you will find plywoods of various plies, from 3-ply to 5-ply and more. The greater the number of plies, the stronger the plywood, and the greater its thickness.
There are other distinctions in plywood products, but for our purposes today they are not germane to the main question of joinery of plywoods.
Considerations When Joining Plywood in Pocket Joinery
First, let’s answer the primary question: you can use pocket holes on plywood. However, there are some considerations you must take into account when doing so. Those considerations include the thickness of the plywood, the type of screw to use, and the style of the screw.
We mentioned earlier the screws to use with softwoods such as pine, cedar, fir, and spruce. Plywood falls into the same category of softwoods when choosing pocket screws.
Thus, you will want to use a coarse-thread screw. They have deep and aggressive threads on them that will dig nicely into the soft fibers and create a tight joint.
For the screw length, the jig setting and the depth of the drilling will determine the length of the screw to be used. You want the screw to reach at least half of the thickness of the bottom board – the one being screwed into.
As it happens, Kreg jigs come with charts that are filled with details to help you determine the right depths. The most common thread lengths run from 1” to 2 ½“. Again, the length of the screw will be determined by the depth of the drilling, with the depth of drilling depending on the boards being joined.
We read many woodworking bulletin boards when researching for this article, and found discussions from woodworkers who regularly join ½” plywood using pocket holes. Some even reported great success joining ⅜” plywood using pocket holes.
In each instance, these experienced woodworkers offered a few tips:
- A 1” screw was the right size for plywood of that thickness.
- The depth guide on the drill needs to be only enough to allow the screw to just reach the midpoint of the board being screwed into – the bottom board.
- Do not use an impact driver when screwing, and be gentle when screwing generally to avoid going through the bottom board or splitting/ripping the bottom piece.
- Use a pan head nail so when finished screwing into the bottom board the head will not protrude above the pocket hole. This is especially important if you intend to use plugs to hide the hole.
In one of our previous articles on pocket hole joinery, we referred to a video that presented an excellent project building shelves using pocket hole joinery. It seems we were a little prescient using that video because the shelving unit being built used plywood for the project. The woodworker in the video also used plugs to hide the holes.
So, we’re recycling the video because it has the best of both – pocket hole joinery, and joining plywood. We did not find a better one to present to you today.
Join away on your plywood projects. Grab your Kreg jig, drill, and screws, and have at it. Join plywood with confidence following the tips we’ve provided, and your project will turn out well.