Pocket holes have become a mainstay in carpentry and woodworking over that past few years, and there are several different makes and models available. But all these models rely on the same basic principal; cut an angled hole from the face of a board towards the edge of the board, allowing you to counter sink a screw through the edge grain or end grain into the mating board. A common question though is ‘What size pocket hole screw should I use?”
Seems simple enough, yet depending on the thickness of the mating boards, the pocket hole jig must be configured to position correctly and to the appropriate depth so that the board is securely fastened and the screw doesn’t protrude through the other end of the joint. The correct length of screw must also be used to ensure correct depth of penetration.
Regardless of platform, pocket holes are limited to joining 1/2″ thickness to 1/2″ thickness. Any thinner and there would not be enough material to contain the screw head and not enough thickness to hold the screw. But above 1/2″ anything is game.
Pocket Holes Made Easy?
There are two main factors when determining the length of screw required. (Refer to Image 1 below)
- The Thickness of ‘board 1’ receiving the pocket hole.
- This thickness can range from 1/2″ thick to as thick as you like. Of course, a very thick board (Greater than 1-1/2″) would benefit from adding pocket screws to the opposite face to even out the clamping force.
- The thickness of the adjoining board.
- This thickness is limited to 1/2″ minimum, but there is no practical upper limit.
Screw Length Chart
So what is the right screw to use? Below is simple guide (Image 2). Refer to ‘Image 1’ above for Board 1 vs. Board 2.
Note that the Pocket Hole Jig manufacturers do not list screw lengths for situations where the mating boards vary in thickness.
Common Pocket Hole Issues
So what can go wrong?
- Most commonly, the user selects the wrong screw for the joint and either the screw doesn’t engage deep enough (easily fixed), or the screw pops through the other side of the joint (not so easily fixed).
- The last variable is setting the drill depth stop accurately and this varies from make to make, so double check before you start drilling a bunch of holes and realize you’ve made a mistake.
- It’s also a good idea to make a test joint with some off-cuts to make sure everything looks good.
- Armor Tools Pocket Hole Jig actually color code their screws to avoid this confusion.
- The screw splits the board apart. This can be due to a couple reasons:
- If you are using pocket holes on hardwood, it is recommended to predrill the holes prior to installing the screws.
- Using the wrong type of screw. Pocket hole jigs leave flat bottomed holes and require a flat head screw. If a countersink head type screw is used it will cause the hole to split open.
So there you have it. I hope this simple guide helps you succeed in your next pocket hole project. Happy Drilling!
Related: Wikipedia: Pocket-hole joinery
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