Timber movement allowance

[Sawdust=manglitter]

I was designing a timber frame building this morning in work and was having a look through the British Standards when I spotted a clause that I've not needed to consider in timber frame design before. There may be more accurate info/rules of thumb for timber movement in furniture making, but thought this might be of use...

 

[custard]

If you want to go further into this subject an excellent guide is an HMSO publication called "Handbook of Hardwoods". It's out of print now but copies still surface fairly regularly.

That would tell you for example that if European Oak goes from 90% humidity environment where it will have 20% moisture content, down to 60% humidity with a 12% moisture content, then it will shrink 2.5% on the tangential face and 1.5% on the radial face. It gives that information (and an awful lot more besides) for hundreds of different timbers.

 

[Sawdust=manglitter]

Thanks Custard. Think I'll keep an eye out for that book, sounds very useful!

 

[John15]

If you want to go further into this subject an excellent guide is an HMSO publication called "Handbook of Hardwoods". It's out of print now but copies still surface fairly regularly.

That would tell you for example that if European Oak goes from 90% humidity environment where it will have 20% moisture content, down to 60% humidity with a 12% moisture content, then it will shrink 2.5% on the tangential face and 1.5% on the radial face. It gives that information (and an awful lot more besides) for hundreds of different timbers.

Thanks for the heads up for 'Handbook of Hardwoods' Custard. I received a copy today - very interesting book.

John

 

[RossJarvis]

I made some green oak "trusses" for a roof last year. The engineer specified "steel pins" to hold the joints. I decided to ignore this and draw-bored and pegged or wedged with seasoned oak. In the past year I've bashed the wedges in to take up 1/2" of shrinkage on 6" beams and the tapered pegs go in a bit every couple of months. I'm probably stupid for following those know-nothings who did frames in the past and wonder what it would look like if I'd used the steel?

In terms of using the tables I sort of go by the "if it looks right......" school of thought.

 

[MarkDennehy]

If you want to go further into this subject an excellent guide is an HMSO publication called "Handbook of Hardwoods". It's out of print now but copies still surface fairly regularly.

BTW Custard, meant to say thanks for that recommendation.

Bloody marvellous little books, and cheap as chips off abebooks.

 

[MikeG.]

If you want to go further into this subject an excellent guide is an HMSO publication called "Handbook of Hardwoods". It's out of print now but copies still surface fairly regularly.

That would tell you for example that if European Oak goes from 90% humidity environment where it will have 20% moisture content, down to 60% humidity with a 12% moisture content, then it will shrink 2.5% on the tangential face and 1.5% on the radial face. It gives that information (and an awful lot more besides) for hundreds of different timbers.

Through experience, rather than reading a book, European and English unseasoned oak will shrink up to 8% across the grain as it seasons. This is easily measured by measuring plaster gaps around oak framing, but is complicated by twisting and bowing, and the tendency for the section to parallelogram..........thus should be treated as a rule of thumb rather than anything definitive.

Edit.......8% of 150mm is 12mm, confirming the post by Ross jarvis above.