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I am learning furniture building. I started by building tables using pocket hole screws to attach the planks together and also to attach the table top to the apron/base.

I am now converting to using fasteners, such as table buttons, Z-clips, etc., to attach the table top to allow for expansion and contraction.

My question is, if I am properly using fasteners to attach the table top, allowing for it to expand and contract, will pocket hole screws allow the table to expand and contract as it is supposed to?

grfrazee
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ScottK
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  • IMHO you should never use pocket hole screws on any tabletop. It might work on a picnic table. There is a reason mortise & tenon Has been used 100-150 years after nails/screw are used in the wood working world. It is better & not that hard to make, a router, or a hand plane & chisel/hammer & you can make the mortise & tenon. – joel LeGrand Dec 24 '19 at 02:51

3 Answers3

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Do pocket hole screws allow for proper expansion and contraction in planked table tops?

It completely depends on where they're sited. They're perfectly acceptable in some places and utterly wrong in others.

Refer to this previous Question, What general considerations do I need to take into account for wood movement? for more info on that regard with some more useful info in this Answer.

Anywhere a pocket screw (or any other fastener, or glue) restricts the ability of cross-grain wood joints to expand and contract as they need to with changes in internal moisture content you have a problem — either the fastener has to give (breaking or bending) or the wood has to give (breaking free of the fastener or if it can't bowing and/or cracking overall). Slightly off-topic: this is one reason that some hammer-and-nails carpentry can appear to break the rules, it's because nails allow for some movement in part because they're mild steel and can bend a bit.

To give a specific example for anyone who has trouble visualising where pocket holes work OK and where they're a bad choice I'll take a section of the image posted by grfrazee and highlight the badly placed ones:

Pocket screws used badly

Note: in the long apron that trio of screws would be matched by another trio on the facing apron, that's why they're not suitable. In only one apron you could get away with it... assuming the top were not glued down and screwed in place rigidly as this plan calls for!

I am now converting to using fasteners, such as table buttons, Z-clips, etc., to attach the table top to allow for expansion and contraction.

In case it's of help, my two favourites are shown in this Answer.

Community
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Graphus
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will pocket hole screws allow the table to expand and contract as it is supposed to?

I'm assuming you built something that was fastened together along the lines of this

table
(source)

where you used pocket screws to attach the individual boards together.

You mentioned that you are switching to more movement-capable fasteners to attach the table top to the base, which is good. Otherwise, there should be no issue with using pocket screws to connect the individual boards together - it will more-or-less act like a glue joint.

grfrazee
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  • Yes, that is how I am building the tables. Except now I am going to start using metal clips to attach the top to the apron, and not make bread boards anymore, to allow for proper expansion. And was just checking that using pocket holes to attach boards would still be okay. – ScottK Mar 17 '16 at 22:18
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In order to determine how and where to fasten wood parts together remember that wood expands and contracts differently in length (tree vertical), radially (from center to outside) and tangentially (generally parallel to growth rings) due to factors like temperature and moisture content. For most woods, change in length is negligible and radial movement is generally half the amount of tangential movement for the same dimensions. Connecting woods with the same directional orientation is fairly safe since the movements are similar. The problem shows up when you connect boards with different orientations. On a table top all of the boards for the top surface are moving in the same directions, but when you mount the top to the base problems arise. Securing the table top to the sides parallel to the top boards will not cause stress along the length of the apron and top. The problem arises across the top. The table top width will expand and contract while the apron at the ends will not since its length orientation relative to the top is not moving at the same rate. If you connect the top and apron continuously with screws (or glue), stress on the connection will increase as the table width and relative movement increases. Eventually, the screws will strip out or the top boards will buckle. Connectors such as buttons or z clips are better since the top can expand and contract in slotted connections to accommodate the different rates of expansion.

As for using pocket screws to join the top surface planks, You get a much more uniform surface with glue without developing gaps since the boards connect continuously.

Ashlar
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