Board width in relation to timber movement

[Josie]

Hello!
I was wondering if there are any general rules surrounding the maximum width of a piece of solid timber, with regards to reducing movement.
Obviously timber will expand and contract regardless of the dimensions, but is there a certain width that doesn't show movement as much? (Thinking in terms of strips that would be joined to produce a wide panel)

Thanks!

 

[Inspector]

Doesn't matter if you use a wide board or a hundred thin strips glued together to equal the width of the wide board, the amount it will move is the same. It might reduce cupping and warpage a bit though. Here are a couple calculators that shows how much the wood will move as it gains or looses moisture.
http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkagehttp://www.woodbin.com/calcs/shrinkulator/
Pete

 

[Josie]

Doesn't matter if you use a wide board or a hundred thin strips glued together to equal the width of the wide board, the amount it will move is the same. It might reduce cupping and warpage a bit though. Here are a couple calculators that shows how much the wood will move as it gains or looses moisture.
http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkagehttp://www.woodbin.com/calcs/shrinkulator/
Pete

Great, thank you Pete!

 

[profchris]

The important trick is designing to allow the wood to move without destroying the thing you've made. I know of three ways:

1. Design so that variable width doesn't matter. Example: a table top attached with buttons. It's a bit wider today than yesterday, but not enough to notice.

2. Put it in a fixed width frame, but with space to grow wider and narrower. Example: panelled doors with floating panels.

3. Redirect the movement to preserve the structure. Example: a guitar back is domed, so when the wood expand and contracts that raises or lowers the dome by a mm or two, rather than cracking the back.

There are probably others I don't know about.

 

[Just4Fun]

There are probably others I don't know about.

Or others that you simply forgot to mention.

You can sometimes account for movement in the joinery. For example a shiplap joint rather than a straight seam.
There must be more. Could be a useful list to compile and keep as a sticky.

 

[Jacob]

Or others that you simply forgot to mention.

You can sometimes account for movement in the joinery. For example a shiplap joint rather than a straight seam.
There must be more. Could be a useful list to compile and keep as a sticky.

Good idea. It's absolutely fundamental to how wooden things are designed/made.
Drawer bottoms fixed on one long grain edge only.
Panels ditto, or fixed with glue dab in centre only of end grain edge, or not at all
Drawer runners in sold carcasses (going across the grain) fixed at one point
T&G or floor boards nailed but unglued to allow small movement at each join rather than big one at the edge.
M&Ts pinned near the joint to keep it tight with any movement at the other end
Slotted screws in many constructions

 

[Billy_wizz]

The important trick is designing to allow the wood to move without destroying the thing you've made. I know of three ways:

1. Design so that variable width doesn't matter. Example: a table top attached with buttons. It's a bit wider today than yesterday, but not enough to notice.

2. Put it in a fixed width frame, but with space to grow wider and narrower. Example: panelled doors with floating panels.

3. Redirect the movement to preserve the structure. Example: a guitar back is domed, so when the wood expand and contracts that raises or lowers the dome by a mm or two, rather than cracking the back.

There are probably others I don't know about.

Would the sound of the guitar change slightly with the movement?

 

[TheUnicorn]

Slotted screws in many constructions

you've lost me there how does a slotted screw allow more movement than a pozi, philips or torx?

 

[Inspector]

Slot in the wood with the screw in it. There is room for the wood to move side to side by the screw.

Pete

 

[Jacob]

you've lost me there how does a slotted screw allow more movement than a pozi, philips or torx?

Sorry I meant screws in slotted holes so the wood can move sideways. They have to be round head with flat shoulders and a washer. Not countersunk. You see it on the back of drawing boards and similar.

 

[TheUnicorn]

Slot in the wood with the screw in it. There is room for the wood to move side to side by the screw.

Pete

Sorry I meant screws in slotted holes so the wood can move sideways. They have to be round head with flat shoulders and a washer. Not countersunk. You see it on the back of drawing boards and similar.

thank you both, that makes sense

 

[Simon89]

R

The important trick is designing to allow the wood to move without destroying the thing you've made. I know of three ways:

1. Design so that variable width doesn't matter. Example: a table top attached with buttons. It's a bit wider today than yesterday, but not enough to notice.

2. Put it in a fixed width frame, but with space to grow wider and narrower. Example: panelled doors with floating panels.

3. Redirect the movement to preserve the structure. Example: a guitar back is domed, so when the wood expand and contracts that raises or lowers the dome by a mm or two, rather than cracking the back.

There are probably others I don't know about.

re the guitar back, why is the back curved to allow for movement and the front flat? I’d have thought that a similar pairing of materials & construction would keep everything balanced? (Disclaimer I know nothing about guitars)

 

[profchris]

The top is usually domed too, but less visibly.

To answer Billy_whizz, the sound might change a bit as the top rises and falls, but you'd need good ears to hear it. The main change us the height of the strings above the fingerboard, which changes how it plays.