ideal moisture content for making furniture

[hawkeye48]

I have just bought some rough sawn oak timber to make a matching dining room table and coffee table.

The oak is air dried and at 15/16%, I was goig to leave it in doors till next Feb/Mar.
What moisture content should i be looking for.

 

[Dibs-h]

I have just bought some rough sawn oak timber to make a matching dining room table and coffee table.

The oak is air dried and at 15/16%, I was goig to leave it in doors till next Feb/Mar.
What moisture content should i be looking for.

Just over half that springs to mind for some reason.

 

[Bkn]

What is the advantage over letting the wood dry naturally rather than using artificial heat?

 

[JoinerySolutions]

Lower than 10%, preferably 6 to 8% which is normally only possible when your workshop conditions match that of the house the furniture is going into.
One way to help it along is to store it in the room or house for several weeks prior to machining, in the past I have stored English Ash in the clients home then machined the boards to give an oversized planed stack of boards. Left for a few more weeks and then machined to final size.
Happily all the work was done on site due to the amount of work for the client we set up a mini workshop in the dining room . the process may seem overkill but the timber was his own and had been converted a year earlier, it worked though and project was a success.
Rob.

 

[hawkeye48]

thanks for that Bkn, as i said it is in my house stacked with small risers to give good air circulation.

I seem to remember 6 to 8 % from when i made our bed many years ago.

 

[JoinerySolutions]

What is the advantage over letting the wood dry naturally rather than using artificial heat?

Cheaper but time consuming, approx 1 year per inch thick. Eco friendly!
Much kiln dried timber is not dried down to much less than 18%, some of it is dried to below 23% for shipping to avoid fungal growths starting.

Having a knowledgeable and trustworthy supplier is a must for quality work and a decent moisture meter that you take time to learn to use properly is good insurance. Once saved my builder and his client a small fortune when I proved that all the doors we had been supplied were "wet" and all the panels had split a week after installation.

Rob.

 

[RogerM]

I think it also depends on where abouts you live. In Devon, even kiln dried oak stabilises indoors at about 13%. I have some air dried English Oak which has stabilised at around 15% after 3 years, and which hasn't changed in the last year. I suspect these figures would be lower in the east and south east of the country.

 

[ondablade]

It might help to put this information up again.

There's a copy of the relative humidity (RH)/equilibrium moisture content (EMC) chart for most woods well down this page: http://www.artisansofthevalley.com/ed_drying.shtml

There's a nice summary of the issue of moisture in wood too.

It varies a little for this for some species and with changes in temperature, but not by much. The bottom line according to the theory is that the percentage moisture content your wood (eventually) settles to is determined by the % relative humidity (%RH) - how much moisture there is in the air versus what it can hold when saturated.

Over here our annual average %RH is around 70% (and it stays fairly close to this outdoors on average winter and Summer - Devon probably won't be a lot different), so air dried wood in sheltered outdoor storage should eventually equilibrate to around 13% EMC as Roger says.

The complicating factor which most of you will be familiar with is that if you take air at a given % RH and heat it (as in a heated room in winter), the % RH drops rapidly as warmer air can hold more moisture.

So Winter air that outdoors was at 70% RH quickly drops to say 45% RH with central heating indoors. Which from the chart is equivalent to around the 8% EMC mentioned above.

There is on the other hand little or no heating indoors in Summer, so the %RH remains little changed from the 70% average outside - unless that is air conditioning/de-humidification is used. So the wood will try to move towards the above 13% EMC.

As before the process is slow (but is much faster in unsealed end grain - which is why ends can warp and split), even more so when the wood is sealed under a finish so in practice it seems the EMC doesn't vary all that much, and the resulting movement can be handled by appropriate design.

This is of course just the basic theory, there is of course a whole body of practical methods that have built up to deal with this situation in practice.

A well regarded book covering all this and more is 'Understanding Wood' by Bruce R. Hoadley from Taunton Press. (the US publishers of Fine Woodworking)

 

[JoinerySolutions]

Roger and Ian,
with my moisture meter I also got a chart to adjust readings for differing timbers and local ambient temperatures, I believe this is due to the variations in temperature and humidity. Leastways it has never caused me a problem either in the UK nor Greece or Germany where it has also been put to work. I did however re-calibrate it in each new locality.

The question of relative humidity is of great concern to our American cousins in places like Florida, the USA forums are often discussing this, particularly among finish carpenters when discussing wood sidings.

When it matters I check and check again.
I agree whole heartedly with Ian here,
Quote
"and the resulting movement can be handled by appropriate design. "

Good joinery and furniture should always be made with respect to what nature will throw at it, appropriate design says it all.
Regards Rob.