moisture level

[bigbob2]

recently bought myself a moisture level meter, as even though I build nearly all glass bows I do use a fair amount of wood I source myself from logs etc I  believe 12% is about the optimum level most go by? Our weather here at the moment is not very palatable being around the 100* F. and humidity probably in the high 80's. After checking some wood that I know is 'seasoned' [commercial lumber] it returned a value of around 18% when I would have thought it should be around the 12%. Any opinions about reasonable moisture content and would a short spell in my hotbox remove this 'extra' humidity induced moisture?

[mikkekeswick]

Wood is always seeking E.M.C. The level this is at is a combination of the relative humidity and the temperature.
 http://www.csgnetwork.com/emctablecalc.html
Have a look at the table below the calculator and see the relationship between the two.
'Seasoned' wood from the woodyard.....umm unless your woodyard has humidity controlled buildings and you live somewhere humid then your wood is very unlikely to be at 12%. I pretty much always resaw what I get now straight away, stack it with good airflow and weights on top and then let it reach emc with my workshop. When I want to use a piece for a bow I bring it inside for a few days - because the pieces are thin they will dry quickly with little danger of checking.
Bigger pieces for risers etc I play by ear and just let them dry slowly.
Beware of putting too much faith in your moisture meter as they are notoriously inaccurate. Unless you've bought a really expensive one that allows you to input different resistance values for different woods. The table above and a weight scale never lie!

[bigbob2]

thanks Mike for your very informative answer. The moisture meter is not a very expensive one , but scanning the tables you posted , given the approx. ambient temp.and humidity the values I obtained were right on the money for the wood I sampled.Thanks.

[BigJim]

Moisture level of wood is tricky and the meters...even the best ones will only read so deep ...typically about a 1/4". The outside will always be drier than the inside.

Additionally if you don't change the numbers of the moisture meter to the density of your wood, you readings will mean absolutely nothing.

Riser sized materials can take years to completely dry even in a ideal environment. You will generally want to use wood that is in the 10% or lower category when gluing.

Most wood issues get blamed on oils and glue starved joints, when they are most likely caused by moisture.

bigjim

[bigbob2]

The meter I have uses electrical resistance between the probes and although the probes are about 1/2'' deep I realise any reading will at best, be close to a surface measurement but I think it might play a part in referencing timbers by interrelating data between various pieces I use.

[mwosborn]

The one thing I do like about my meter is that it does allow you to compare the moisture in the same piece of wood over a period of time as it is drying out - even if the actual moisture is inaccurate it is telling you if it is decreasing over time.

[bigbob2]

that's basically what I reckon I will be doing, using it as a yardstick so to speak.

[BigJim]

Cut some pieces you like to as small as you can use them plus a little to allow for shrinking and then a little more so you can true them back up as they will likely warp or twist.
Wax the ends and put them under your bed, or some place in the house the wife won't complain about too much and then forget them.

When cutting veneers, it is best for them to be at least slightly dry or you will end up with potato chips/bacon looking critters, but they can be used within a couple weeks after cutting.

2" thick pieces may take a couple years depending on density.
At least here in the states, most homes in high humidity areas have AC and this reduces the humidity in the house to very low levels. It is also kept considerably cooler than the barn.

The slower you dry it, the less issues you will have with it.
Take riser block size pieces and put them in a paper bag and tape the end up. Weigh it and write weight and date/species and any other pertinent info on the bag. Give it a few months and then weigh it every week. When it stops dropping weight for three weeks in a row, it is ready.

BigJIm

[Buemaker]

It is easy to measure the moisture level in the middle of a thick plank, with a pin moisture meter. Just hammer in two nails as far apart as the pins on your meter is apart. Place the pins in contact with the nails heads and take your reading. If the wood is too hard to hammer in nails just drill two small holes, a little smaller than the nails and smack em in.
If you doubt the correctness of this way to do it, just check it out.
The calculator that Mikk posted is fine if you have the correct humidity, for that you need an accurate hygrometer. The catch is that hygrometers are notoriously inaccurate. I have three of them and they all show different readings. Even after calibrating the three of them to the "same" zero they still show different readings. A few years ago there was a thread on the PowPow about hygrometers, seemed to be an extensive field, perhaps someone could dig it up ( I can't find it) Bue--.

[bigbob2]

thanks Jim and Bue. I have been doing some weight analysis with some woods, but don't have aircon but under side of house is reasonably cool and where I stack my wood separated by sticks. Bue good idea re nails , will try it but as you say won't be able to get an accurate humidity reading in any case.

[George Tsoukalas]

I like hickory at 6-8% and all other woods at 8-10%.

I keep using my meter throughout the bow making process and won't string the bow unless the wood reads at the proper mc.

Jawge

[bigbob2]

At this moment the humidity here is around 80% + according to idiot box.

[mikkekeswick]

You don't need an humidity reading to be accurate to tenths of a percentage point! Afterall it varies quite a bit from day to day....
What you are looking for with humidity readings is an average for a time period. A quick glance every other day is all you need to get an idea what's going on.
As BigJim says the safest way to dry wood, any wood, is slowly.
I would say that a moisture meter is probably at least as inaccurate as a humidity meter!
Weighing the piece of wood is alwyas going to work no matter what you just need an accurate weighing scale.
The other option is to cut off a scrap piece weigh it straight away and then put in the oven/microwave etc to get it completely dry and then weigh again. The difference is your m.c.
This method is failsafe and quick....but you need to be willing to spare an offcut.

[bigbob2]

I have used that process with smaller pieces Mike ,and in future will endeavor to do much the same with any wood I get in.Always pays to be aware of all processes one can use when in playing about with wood, as any failure could be very detrimental in a number of ways!

[beachbowhunter]

Oh crap, another variable to worry about!  

[JamesV]

I bought a cocobolo turning blank 1 1/2 X 1 1/2 X 18". It was almost dripping wet when I got it. For am experiment I put it in the freezer for two days, took it out and scraped the frost off then stood it on the end and let it thaw on the counter, it had a puddle of water around the base after it thawed. Dried it off and back to the freezer and each time it had less water when it thawed. After about a dozen sessions it was almost dry, then to the hot box for a few weeks, the grain was horrible so I never used it but I think it was dry enough.

James

[mikkekeswick]

Interesting idea!

[bigbob2]

That is one unconventional way to go about it but seems like it would be worth a shot! Could weight it before hand and continue to measure weight loss each time until it stabilises. It seems one possibility when using external sources like a hotbox, it is possible to 'case'harden the wood leaving a hard dry outer 'skin'and a soft moist core, which would set up shear forces if nothing else.

[George Tsoukalas]

Very interesting. Remember that water expands when it freezes. That could result in a stave with cracks. Jawge

[Roy from Pa]

That's what I thought too, George....