How to stop table tops bowing

[Cornwall360]

Hello all
I’m going to be making some tables shortly, new venture, never really done it before,(mainly cabinets currently), but looking forward to it.
My concern is the tops bowing.
I understand the wood needs to be dry, around 8-13% moisture content.
I’m worried I might not quite get the wood that dry as it’s in a workshop that is slightly damp.
The wood is likely to be 13-20%.
Are there additional methods I can take to help stop the boards from cupping, twisting, and basically end up ruining the table once it’s in the customers home?
Thanks

 

[Ttrees]

Is drying it out in the house an option?

Tom

 

[Jason Wheeler]

C-channels running across the width of the table - drill inserts the bolt them

 

[Fitzroy]

Traditionally this was the purpose of breadboard table ends. Also a thin top, under an inch, is pretty flexible and if you have a traditional table frame then it’ll be held flat against this.

 

[Blackswanwood]

What size is the table and what size board are you using?

 

[Cornwall360]

What size is the table and what size board are you using?

Table will be 1.8 meters long, using jointed scaffold board. Pretty basic top to begin with

 

[Cornwall360]

Is drying it out in the house an option?

Tom

Yeah could be, I heard this still takes up to 6 months though

 

[Blackswanwood]

It depends on the environment you keep the boards in as to how quickly the moisture content will drop. If you do it too quickly (with artificial heat) you may well find it induces movement. A mildly heated room (or polythene tent) with a dehumidifier may be worth considering.

When you edge joint the boards ensuring the growth rings on adjacent boards are oriented opposite to each other as this will help minimise any cupping.

The wood database website has some useful information on drying timber.

 

[Ttrees]

Might depend on the thickness I suppose, and how best you can stack them in the house.
A test run might be quite insightful, few offcuts, sealed ends, infrared thermometer gun,
one is likely to see much variance, but that's just a guess.
I've done my glue ups inside, that's when it's below 10 c for some sustained period in the shed.
Here's a recent enough thread on scaffold planks, seems it could be deserving of a bump.
https://www.ukworkshop.co.uk/threads/are-scaffold-boards-getting-thicker.142697/#post-1662567
Just mentioning, as I've not studied many scaffold planks, to see if indeed there might be some quartersawn stock to be obtained from such.
That, and as little runout on the edge grain as you can find, if such luxuries are possible.

If only flatsawn, "through and through" available, find the planks with the straightest end grain,
should the example be free from sapwood, and the pith,
and as the same with QS grain planks, run an eye down the edge to look for runout.
Richard, @Sgian Dubh in the link has some excellent posts concerning this area, worth looking in the search.

Those things first for the best bet, along with trad options mentioned for sure, and cross yer fingers it won't move that much, as I doubt.. unless you've got stacks of planks to choose from,
that the timber will have the best qualities for use in furniture making,
and saying that, I've no clue whether or not if say, only flatsawn or riftsawn is specified?

All the best
Tom

 

[Cabinetman]

Just occurred to me, are you planing the edges and gluing or are you going pub table with gaps?
Nicely put Tom.
My Son recently covered his bedroom wall with s/planks then built a wardrobe against it.
Wouldn’t do for all of us to be the same would it!

 

[dzj]

As Ttrees said, choose your stock wisely and stay away from planks exhibiting any of the aforementioned problems.
Bowing is probably not going to be a problem if you have a nice sturdy apron/ frame to attach the table top to.
Cupping might, though, if you plan to use wider stock. This can be minimized by making lengthwise (stopped) kerf cuts.
Tell your client that this is not furniture-grade stock and slight imperfections could show over time
HTH

 

[Hornbeam]

You really need to try and get your timber as close as possible to its final environment. Once I have rough cut all my components they go into the spare room until I am ready to start.
You have a couple of things to consider.
Cupping and twisting. By alternating pieces you will minimise overall movement but will induce an s curve
You can limit cupping by either fitting breadboard ends or slot screwing battens . In practice the battens can be the underframe of the table. I dont see any need for metal battens or recessing them into the underside
Shrinkage. As the wood dries it will change very little along the length of the grain and about twice as much across the grain as radially ( this is why square sections of unseasoned wood go into diamond shapes.
Shrinkage across the grain must be allowed for by slot screwing of battens and if fitting breadboard end these must allow for movement. It also means that the end will nearly always have a step to the main table section