Thread: slab dining table

How wide is the slab? If you don't mount it so it can move a little it
may split later. how about some metal L's and use pan head screws
to attach to the table so it has some play. Use the flat heads to
attach to the rails. One every 200/250 mm should hold it down.

hi papa, the slab is 1220mm wide 2350mm long.

Originally Posted by bench1holio

hi papa, the slab is 1220mm wide 2350mm long.

Some sort of sliding connection for sure, A slab that size could move maybe 1% seasonally, and thats about 12mm. Some sort of tabs into a grove or slotted joint for sure.

The length wont change noticable, so you can ignore that.

Ian

Ian is right a slab that wide can quickly change by 12mm with a change in humidity. Cedar is more stable than some but can still cause you greif if the movement is not controled. You have to allow the top to move while still being held in place, once you have sealed the slab (all over) you will get less movement (also depends what you seal it with). The more air/moisture tight the better.

Originally Posted by bench1holio

....in the time it has taken to build the legs and rails the slab has moved quite a bit leaving a gap of nearly 10mm between slab and rail on one side.

I read this as the slab has cupped, not simply shrunk, though it has probably done a bit of that, too. In that case, trying to pull the slab down onto the frame could end up twisting the frame, depending on its construction & the thickness of your slab - i.e. which is the more rigid of the two. The best cure would be to re-flatten the slab before fixing (which should always allow for some seasonal movement, of course). This would depend on how much thickness you have & how much you are prepared to sacrifice.

Your slab was obviously a bit 'wet' for the environment at the start - if it has now reached EMC at a median sort of humidity for your area, it's worth considering re-flattening, but if it's still got a ways to go, you should hold off until it settles down. A slab that wide would have to be plainsawn from somewhere near the centre of a log, so it is set up for cupping as it dries. Cedar is pretty stable stuff, as claw hama said, & soft enough not to generate huge amounts of force when it does grow & shrink a bit with the seasons, so you should end up ok eventually.

Cheers,

I'd be wary of trying to pull the cupping out of your slab because of the risk of splitting it.

Ian and Claw Hammas advice seems spot on. If you look at the end of your slab you will see the growth rings and how they have pulled the slab into a cup as it dries. If the slab was lying on something flat as it dried then there would have been less airflow on that side and so that side would have dried slower than the other side. Wood expands with moisture and contracts with dryness; this difference may have exacerbated the cupping.

If you turn your slab over and make sure that you get airflow to that other side then you may reverse a little of the cupping. Probably you will have to re-thickness the slab when it is fully stabilised. Those comments about sliding attachments are critical.

I endorse ClawHammas request for a photo. An 8x4 ft red cedar slab should be spectacular.

Cheers

Graeme

By the sounds of what your describing your slab has twisted ( I could be wrong ) but if it has, probably best to plane the slab so its sits flat on your rails - other wise you may end up with a wobbly table if you screw your slab onto your rails.

I might suggest using a sliding dovetail or

cut some slots into your rails and make some wooden brackets sit inside the slots and screw your slab onto your rails. Theres a term for these brackets just cant remember right now.

Originally Posted by KorDes

Theres a term for these brackets just cant remember right now.

I think they are called buttons

hi all, thanks for all the replies, the slab has actually bowed along the legnth of it,hasnt cupped much at all, i put a straight edge on it today and clamped it flat which didnt take much strain, then thought maybe if i beefed the rails up inside with hardwood maybe that would hold it .
(thinking it would be less likely to split along it!), which still doesn't allow for movement.
also its only 35mm thick so cant really machine it again.

From the sound of that, it shouldn't be a problem - I'd just attach it (with buttons or whatever method you choose that allows a little lateral movement) & keep an eye on it.

Beefing up the long rails, if it's easy to do would be a bit of insurance, but may not be necessary if it takes very little force to spring the bend out.

Cheers,

And it is only Cedar, it doesn't take much to keep it where you want it, unlike some of our less cooperative hardwoods.