• We invite you to join UKWorkshop.
    Members can turn off viewing Ads!

rate of expansion/contraction for oak

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

Mister S

Established Member
Joined
6 May 2011
Messages
120
Reaction score
0
Location
Southport, Merseyside
Hi All

I am in the middle of using some well seasoned (reclaimed) oak to make the top and bottom for a box, about 20cm in width, sitting in grooves in the sides.

Any idea how much allowance I should leave for seasonal expansion/contraction? A figure of 1% (which would be 2mm) jumped into my mind, but I can't find a reference to rates of movement anywhere. I don't want to make the grooves unnecessarily deep as it would weaken the sides.

Any ideas?

Thanks
Steve
 

Mister S

Established Member
Joined
6 May 2011
Messages
120
Reaction score
0
Location
Southport, Merseyside
Just found some web sites that calculate wood movement (American of course - the Shrinkulator :shock: ) , which need variables to be input to give an approximate value.

What would be a reasonable moisture content range for indoors in the uk? I was thinking 10% to 15% but I'm willing to be corrected.

Steve
 

custard

Established Member
Joined
20 Aug 2008
Messages
7,116
Reaction score
542
Location
Hampshire
Steve, average relative humidity levels vary around the UK, in London the external range is from 86% in January to 70% in June, but in coastal areas it tends to be a bit higher but more stable. In Plymouth for example it's highest in January at 89% but lowest in May at 77%. To achieve equilibrium at 80% humidity timber needs to be dried to about 16%, at 70% humidity timber needs to be at about 13%.

However, I find that indoors humidity can be quite a bit lower, in my workshop (London, heated) it tends to be in the range of about 50-60% year round, with only occasional and short moves to 65% or 70% during summer thunderstorms. To achieve equilibrium at 50% humidity timber needs to be dried to about 9%, and to achieve equilibrium at 60% humidity it needs to be dried to about 11%. Consequently I aim for about 10% moisture content in the timber I use for indoors furniture, and 15% for outdoors furniture.
 

Mister S

Established Member
Joined
6 May 2011
Messages
120
Reaction score
0
Location
Southport, Merseyside
Custard

Thanks for the comprehensive reply. As I suspected, "it all depends".

The calculators I have found suggest movement at the levels you have described of roughly 1% to 1.5%. I think I'll aim for that and make the grooves oversize accordingly.

Cheers
Steve
 
Top