So I’m a hobbyist woodworker with only so much knowledge/exp.
I have a two-part question.
I’m building a small(32Wx36L, 72″L w/leaves) kitchen table for my sister out of red oak(the top will be 1/4-sawn).
I was watching this video on how to attach the wooden extension slides ( https://youtu.be/1o687bj1XQM?si=uYwc6W1p9n-J9chl ) and I noticed it looked like they have pocket hole screws attaching the skirt to the tabletop. I did wonder why, and if that’s normal, considering wood expansion. But they seemed a reputable company so I figured I’d get a Pocket hole jig and do that. Then I saw another video talking about pocket hole jigs(I’ve never used one) and he said specifically NOT to do this, confirming my original skepticism.
So my questions are:
1)Why would the company in the above video do this, is it because the expansion over the 18″ half of the table be negligible?
Should I NOT do this?
2) I’m using quartersawn oak for the top, wouldn’t this mitigate expansion considerably?
(I thought I’ve read/saw someone say quartersawn wood expands through it’s thickness because of the growth rings running perpendicular to the face.)
Replies
I’ll be watching this. I’m planning to build a ¼ sawn white oak coffee table in the A&C style. I’ve always read to secure the top with a fixed screw in the centre (across grain) at opposite aprons (2 screws total) and ‘float’ all other attachments using clips riding in a routed channel. Essentially keeping the top from lifting bust allowing movement side to side.
I have actually build small pieces and fixed with a single screw in the centre of the apron, one on each long side, and never added any additional fasteners. My thinking is the weight of the top and the single fastener will prevent it from accidental movement (bad children) while allowing maximum wood movement.
If I don't get any responses I figure I might just screw the apron/skirt to the table top at the end of the apron(middle of the table) on each side(The table splits in the middle to extend).
And use z-clips or something similar in a groove in the apron the rest of the table. This would allow the top to expand ONLY "outward" towards the two ends of the table.
I also really don't think they're be very much expansion with it being quarter sawn, I'm just worried seeing it's not for myself.
I also don't understand why the wooden extension slides that are screwed across the width of the grain wouldn't cause the same problem?
So I got the Rockler slides in. There's no elongation in the screw holes. Nor does it seem there's much space in the holes for movement with what I would imagine would be the recommended screw size.
It just seems weird to me one of the most popular online woodworking source companies didn't account for wood movement.
Also, I took a picture of a table(pic attached) I have that's an antique and although the aprons are not Mortised into the legs or attached other than the corner braces, it does have screws(ostensibly pocket hole) from the apron directly into the top with no apparent allowance for movement. The width of the tabletop(one side) is 13.5 in. Not a tremendous amount of wood but I would assume it could move up to 3/32-1/8.
But no problems with this top warping or cracking and I'm guessing it's 50+ yrs old.
I'll try and cover what I can.
1. Osbourne is a reputable company
2. Quartersawn will lessen the movement
3. Pocket holes attaching an apron is fine, there can be enough room for expansion if done properly
Any movement will be minimal. I would say 3/32" max. This is then divided by two (1 screw on each side). The result is thare really isn't too much to worry about.
A pocket hole is essentially a butt joint, if you're concerned, simply oval out the screw holes to allow for some movement.
Thank you.
Is your estimation of 3/32 because I'm using quartersawn or is that for plainsawn?
Also, I've heard a general rule to be 1/8 per foot(alot of variables though). Do you agree with that?
I have a 54" round walnut dining table, with 2 halves that open up for leaves. It was factory made, and the apron halves were attached with pocket screws. They split one of the table halves into two pieces, as they did not allow adequate room for the movement of the top (and walnut is considered stable; it has relatively low expansion and contraction, and its ratio between radial and tangential is almost 1). Don't attach your top with pocket screws. Use buttons or clips except for the center screws that keep it fixed in place. Don't use just the center screws; the other fasteners are there to keep the top flat. Oak is prone to cupping, tho quartersawn is much less so. The weight of the top is not sufficient to keep it flat.
Make the holes for the leaf extension mechanism somewhat oversize to allow for movement. Sometimes it is helpful to use a washer. I often glue a batten to the inside of the apron, with a normal hole in the middle, and elongated holes out from there.
Thanks for your input.
The factory I worked for built 50 tables per day for over 50 years using this same technique and I ‘ve never seen a split top . The wood was kiln dry maple dried on site and the rails, some straight some half circles were attached with pocket screws. In addition, the extension rails also were cross grain as well as the stiffeners on longer tables, I remember those were screwed in oversize holes.