Isn’t pockethole joinery bad for wood movement?

June 22, 20154 Comments

In the short time since I released the video for Samantha’s table I’ve had a few people asking why I didn’t use a different method for attaching the table top to the apron.

Concerns over top to apron attachment

Concerns over top to apron attachment

Apparently there’s a lot of concern centering around the use of pocket hole joinery this way, more specifically a concern it isn’t allowing enough room for expansion and contraction.

But the reality is, I have all the confidence in the world this table top will have zero issues with it over the years, and here’s my reasoning.

First and foremost is the fact the table top isn’t one solid piece, it’s three individual boards laying side-by-side, three individual boards independent of each other. This is a fact that shouldn’t be overlooked as I continue with the rest of this post.

three board table top

Three independent wide boards for this table top

If the top had been the three boards edge-glued to one another I certainly would have attached it slightly different, but it still would have been with pocket hole joinery (more about that below.)

In fact what I did with the pocket hole joinery is almost identical to what one would do when installing cedar shake siding. You install two mechanical fasteners a certain distance apart from each other on the face of the shake. These two fasteners hold the siding tight to the underlayment but allow the piece to expand and contract as needed without splitting.

rendering of shake siding

Artistic rendering of shake siding

Really the only board on this table top I have any concern with is the one in the middle. But as I pointed out in the video, there’s already a little gap on either side of it since I didn’t joint the edges, and that little gap is plenty for any wood movement I’ll experience in my particular climate.

Again, how does pocket hole joinery allow for wood movement in this situation?

Just like with the cedar shakes each individual board in this table top is held snug to the apron at two points, the rest of the board is free to move across its width as needed, and given that wood can be extremely resilient when it comes to movement it doesn’t care if it’s held in place by a single mechanical fastener in one location or two, the only thing that matters is that it has some way to move. Which in this case it does.

pocket hole joinery

If I had done something like glue the boards to the apron, where it’s trapped across its entire face, then I certainly would have had an issue as it fought to break free.

At this point you might be thinking, “yeah, but for each board you attached it with two screws at various locations along its length, so that’s more than one location right?”

Yes it is, but they’re also all lined up with each other down the length of the board (more or less) and far enough apart that it allows for the needed flexibility in the board.

Now let’s talk about my strategy if I had glued all three boards together to make one large top, would I have attached them differently? Yes and no.

Yes in that I wouldn’t have used as many pocket holes, and no, because I’m still going to use pocket holes, just not as many.

In fact my strategy for attaching the top to the apron in this situation would have been to use a pocket hole in the center of each short apron on the ends of the table plus one in each support, and then three along the length of long aprons. One near each end and the third dead center.

Alternate attachment strategy

I also would have taken the extra time to wiggle or elongate the hole to allow the screw to move as needed when there was seasonal wood movement.

The key difference here being that I would expect wood movement to have a more drastic effect with the glued-up panel than the individual boards, so using this strategy helps to insure it’ll stay in place but not cause splitting or checking where the screws are attached underneath.

This is in fact very similar to what you would be able to do with slotted screw holes, or table top brackets, or such that others advocate using when they talk about the evils of pocket hole joinery.

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Comments (4)

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  1. Matt,
    I think that your thought process was correct and the worst that you will have in the future are small gaps between the boards as time goes by. Easier to get rid of the crumbs in my opinion. Nothing wrong with the pocket screws.

    mg

  2. Mike Holden says:

    Of course you could simply point out that the Townsend/Goddards used pocket hole screws to hold their tabletops on, and 200+ years later they are still doing fine (and are EXTREMELY valuable)

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