Thread: Tabletop - Can I avoid the warp?

G'day David, are you planning on putting a skirt (a.k.a. apron) under your table top at all? That is the most important question here.
If so, I can make a suggestion on how to attach the skirt which will also help prevent the table from buckling due to direct sun or
seasonal changes.

1 - sure, 3-5 inches should be fine
2 - not necessary -- they help with lining up if you attempt to do the whole glue-up in one go, if you glue up in 3 steps you won't need them
3 - I would stay away from breadboard ends
4 - 40mm (1 1/2 inches) you quoted as table top thickness is going to look chunky on a table that size. If you don't want the chunky look, go 20-25mm
it's also easier to keep the top flat with an apron if the top is not too thick (less force in warping)
5 - no
6 - keep the direct sun off the top for long periods, use an apron, use the same finish on top and on the bottom of the table top so it breathes evenly on both sides.

more later, my wife wants to have breakfast.

I use this joint to connect table tops to skirts in order to allow for the different rates of movement along-the-grain and across-the grain with changes in moisture content/humidity:

table top joint 1.jpgtable top joint 2.jpg the block grips into a groove; the rebated part is slightly less than the distance from the
groove to the top edge, hence it pulls the top down onto the skirt.

Boards on this table are approx. 115x25mm, and when the sun burns down on it for a few days in a row it will "prick up its ears", in other
words the corners will lift up a little, but visibly. I try to keep the curtains closed after lunch on the big kitchen window during the hot
months - if/when I remember - so it doesn't catch too much direct sun.

hope that helps give you some ideas, -Peter

Peter, thank you so much for chiming in, really appreciated.
#3 – Just curious why you’d say away from breadboard ends?That’s good news to me as I’d prefer to not have them as well.
#6 – Noted on finishing both sides!
Thank you for your photo, that does make sense re: attachingthe table top. Are those small blocks simply screwed into the table top?
I was originally thinking of placing thin slats goingcrossways underneath to help maintain shape, however, it seems an apron isreally a must, otherwise it’s not going to hold together well long term?
With the apron in mind, is there a general rule for how tallit can be? Basically, I’d like to make it as short as possible, and not righton the edge of the table, so that it appears hidden. Does that make sense?Feasible?

Breadboard ends: the expansion and contraction of wood along the grain versus across the grain are vastly different.
(across the grain moves more) So if you want your breadboard end to stay in place you'll have to use cunning techniques
like a sliding dovetail joint, only pinned at one end in order to avoid things coming apart after a while.

That's why I use the above technique to connect my table tops to the apron - because some of the apron goes lengthwise
across grain - the little blocks allow movement laterally. And yes, they are simply pre-drilled and screwed on with one
stainless woodscrew. Some people use metal angle brackets instead, that also works fine and is a lot less demanding to put
in (don't need a router for the grooves, no rebating required) - I just like the idea of avoiding as much hardware as I can
and there are always some offcuts available for the blocks.

You don't HAVE to put an apron on your table, what with the metal legs you are proposing to use, especially if you make
the top chunky. Aprons provide bracing for wooden legs, a surface to attach them to, and they restrict vertical movement
in the top so it will stay flat better. If you go for a thinner top, they will also add a lot of strength.
On the other hand, if you go for your original idea and use 40mm thick kiln dried oak planks, and you make sure to pick out
quarter-sawn ones - there won't be a lot of warping and the strength will be tremendous.

The size of table you're going to make, I'd go for 60mm-80mm wide boards for the apron, and set them back from the edge by maybe 2-3 inches.
On a larger table you can go in a bit further - ultimately a question of appearance: I am sure there's some kind of "golden number"
ratio, but if so I don't know the formula. I just try to get the visual aesthetics right.

Originally Posted by davidjames

#6 – Noted on finishing both sides!
?

It is a good idea to give the top and underside of a table the same number of coats of finish, this will greatly reduce warping.

When gluing the boards for the top alternate the end grain up and down this also helps to keep the top flat as they each try to cup in opposite directions and there fore hold each other as opposed to all the same direction the top will curl. (I hope this makes sense.)
Regards Rod.

Folks, just wanted to stop by and say thank you for all the advice and tips, it is has been very helpful and gave me all the necessary info and confidence to go forward!

I'd hoped to have made this over Christmas as the only space I have to make it is at my parents place. However, when I got in the garage, it was worse than I had anticipated. I spent the odd moment over the xmas break simply cleaning up the garage, finding and fixing tools, and making suitable workspaces. Honestly, with no exaggeration, there were tools piled on top of each other everywhere, no work bench. I am lucky I came out alive.

I visited them for a couple of days last week, and actually began work on the table, with actual wood. About time! It is going fine so far, I am taking my time so I still enjoy the process. I am ready for gluing & clamping next.

I will try and post a photo when all is complete... it will be a while though given it's located some 3 hours away from me...

I realise this post is getting a bit old, but here a few thoughts.

Breadboard ends are not intended to stop tabletops warping. They don't have the structural integrity to do that at all. They are primarily an appearance solution - so you don't see end-grain, and any splits etc which may develop. These days, most people don't seem to mind end grain as much as they used to.

If you think the top timbers are too heavy, then bevel the edged from the underside. Very common styling technique to make a tabletop look light and graceful. Start the bevel about 75mm out and bring them down to about 10mm at the edges.

I don't get the idea of using a skirt with hairpin legs at all. The idea behind hairpins is so you can use just a lightweight, elegant tabletop, seemingly floating with minimal structure underneath. Very mid- century Scandinavian look - but only works if you keep it minimalist.

The purpose of a skirt on a table is largely to provide strength to the legs (assuming wooden legs), not to prevent a poorly made top from warping.

Use quality kiln dried, season it in your Workshop before use, joint it properly and lay the boards out in alternates, then apply equal finish to top and bottom and you should be ok. Dont try to restrain any warping that might result - it never works. If, down the track, a board warps, slice it out and rebuild.

Just my opinions
Cheers
Arron

Originally Posted by Arron

I realise this post is getting a bit old, but here a few thoughts.

Breadboard ends are not intended to stop tabletops warping. They don't have the structural integrity to do that at all. They are primarily an appearance solution - so you don't see end-grain, and any splits etc which may develop. These days, most people don't seem to mind end grain as much as they used to.

If you think the top timbers are too heavy, then bevel the edged from the underside. Very common styling technique to make a tabletop look light and graceful. Start the bevel about 75mm out and bring them down to about 10mm at the edges.

I don't get the idea of using a skirt with hairpin legs at all. The idea behind hairpins is so you can use just a lightweight, elegant tabletop, seemingly floating with minimal structure underneath. Very mid- century Scandinavian look - but only works if you keep it minimalist.

The purpose of a skirt on a table is largely to provide strength to the legs (assuming wooden legs), not to prevent a poorly made top from warping.

Use quality kiln dried, season it in your Workshop before use, joint it properly and lay the boards out in alternates, then apply equal finish to top and bottom and you should be ok. Dont try to restrain any warping that might result - it never works. If, down the track, a board warps, slice it out and rebuild.

Just my opinions
Cheers
Arron

Thanks Arron.

That is of course the look I'm going for and came here for general construction tips which has been very useful. I haven't yet made the apron, so if you could elaborate, that would be helpful.

For aesthetic purposes I'd prefer no apron

I'd be happy with 3-4 cleats underneath, which would be more or less invisible at the right size.

But how would I then go about bolting the legs to the table? I want to be able to be broken down, add/remove legs when needed. Otherwise, it won't get in and out of the flat. Or the next place, etc, etc.

Does that make sense?

The top is an inch thick.

Would you just bolt right through the surface, with a carriage bolt, and conceal the drill hole with something?

I don't like the idea of simply screwing/unscrewing holes, as I can see them wearing and becoming weak over time.

Thanks for your input.

I'm assuming here you are wanting to make something like in the picture attached - though personally I would have put a bevel on the edge of that tabletop just to aesthetically balance table thickness with leg visual substance.

Anyway, if the top is hardwood then most times hairpin legs are simply screwed in from underneath. They usually have a fairly large bracket which spreads the force out and helps to prevent racking and hence excessive forces on the screws. It might sound a bit fragile but they do seem to stand the test of time.

However, I understand your concern about the screws working loose over time. In that case I would find some screw inserts which are fitted into the table top. They are usually aluminium or steel. You then screw into the inserts, but the point is the inserts make very wide contact with the table top so they are less likely to work loose - and the screw makes metal-to-metal contact as it is driven in so the timber around the thread doesn't degenerate over time. Have a look in your bigger hardware stores - they may have something. Here in Aus I would go to a cabinetmaking supplier or kitchen-maker supplier like Hafele or Nova. Also Google 'screw inserts' - but the solution might come in other forms as there is a whole world of clever custom cabinetmaking fittings out there the problem is knowing what to look for.

When making our dining table I faced the same problem - very heavy top and very heavy legs, but didn't want a skirt. I made up some brackets from plate aluminium which were recessed into the bottom of the tabletop, screwed in place and glued in with epoxy for good measure. The plates are not visible from the side though when you run your hands along the bottom you can feel them. That was about 10 years ago and so far no squeaking, though I admit it does kind of negate the advantage of using hairpin legs.

I definitely would not screw anything in from above.

hairpins.jpg

Originally Posted by Arron

I'm assuming here you are wanting to make something like in the picture attached - though personally I would have put a bevel on the edge of that tabletop just to aesthetically balance table thickness with leg visual substance.

Anyway, if the top is hardwood then most times hairpin legs are simply screwed in from underneath. They usually have a fairly large bracket which spreads the force out and helps to prevent racking and hence excessive forces on the screws. It might sound a bit fragile but they do seem to stand the test of time.

However, I understand your concern about the screws working loose over time. In that case I would find some screw inserts which are fitted into the table top. They are usually aluminium or steel. You then screw into the inserts, but the point is the inserts make very wide contact with the table top so they are less likely to work loose - and the screw makes metal-to-metal contact as it is driven in so the timber around the thread doesn't degenerate over time. Have a look in your bigger hardware stores - they may have something. Here in Aus I would go to a cabinetmaking supplier or kitchen-maker supplier like Hafele or Nova. Also Google 'screw inserts' - but the solution might come in other forms as there is a whole world of clever custom cabinetmaking fittings out there the problem is knowing what to look for.

When making our dining table I faced the same problem - very heavy top and very heavy legs, but didn't want a skirt. I made up some brackets from plate aluminium which were recessed into the bottom of the tabletop, screwed in place and glued in with epoxy for good measure. The plates are not visible from the side though when you run your hands along the bottom you can feel them. That was about 10 years ago and so far no squeaking, though I admit it does kind of negate the advantage of using hairpin legs.

I definitely would not screw anything in from above.

hairpins.jpg

Arron, thank you.

I have looked up screw inserts and they're very accessible over here, I can find them in a variety of sizes so I can get the right depth, and even the right thread type - both for the wood, and for the M10 bolt, so it'll have a good mechanical fit.

Mine will hopefully look very similar to this, although it'll be square. And I think the table top will appear a little thinner (it's only around 1 inch) so will co-ordinate better with the legs. But I'll keep a bevel in mind as well, and have a look at things before finishing.