Moisture, Movement and Meters

[Jerry Wright]

Air dry for 1 year per inch of thickness. You probably won't get to 8% without kiln drying. Air drying is more like 12%. Perfectly acceptable as long as you pay attention to basic rules of expansion and contraction. Lots of fine antiques were built with air dried lumber.

[andy bessette]

Your thread was about a failed attempt at table joinery, which a meter would not have avoided. Now it seems to be more about finding rationalization (milling green logs) for buying a meter. I have been a woodworking professional for over 40 years and have never owned a meter.

[Kevin Jenness]

" So, if you don't have a meter, how do you know when enough time has passed to allow sufficient drying and/or acclimation?"

You can use a scale to monitor weight loss. Kiln operators typically weigh samples to monitor drying rates. When piece of green wood stops losing weight it is in equilibrium with the ambient relative humidity. A meter is a useful tool but not essential.

[Doug Hepler]

John,

Sorry to hear about you gappy table top. I respect your interest in really understanding this issue. To answer your question about moisture meters, see this article: http://www.popularwoodworking.com/am...oisture-meters. It discusses the subject but does not tell you which meter to buy. I have a Timber Check moisture meter (pin type) which has been satisfactory. Precise moisture measurement is not necessary IMO because small changes (a few points) are not associated with large changes in dimension.

Your biggest issue for furniture, unless it will be shipped to another climate, is the change from workshop to indoors, especially summertime outdoors to wintertime indoors. I prefer kiln-dried wood but have used air-dried wood for many projects with no problem.The significance of changes in equilibrium moisture content (EMC) is controversial for a number of reasons, so reasonable people may disagree. My philosophy is always to calculate the likely change in dimension and then allow for it when I design a piece. See this article: http://www.lonniebird.com/wood-moist...y-lonnie-bird/

I think that your problem is mainly the result of attaching the boards to plywood, as already discussed above, and the way in which you glued the edges together. I agree that you would probably not have seen this problem if you had simply edge glued the panel. You would, however, need to account for dimensional changes with EMC when you attached the top to the base. I have seem screws that had been ripped out of their holes by wood expansion and contraction over the years. Specialized clips are made for this purpose to let the wood slide horizontally while keeping the panel tight against the base.

Finally, I have briefly addressed these issue in my book, which is available (free) on the web. Just go to http://plaza.ufl.edu/chepler. Look at chapters 4, 8 and 35

Doug

[Brian Holcombe]

I appreciate the feedback. It's especially helpful for someone like me that is trying to learn the craft via the internet and trial and error.

The last few comments are interesting - essentially downplaying the significance of moisture content and a meter to a point. So, if you don't have a meter, how do you know when enough time has passed to allow sufficient drying and/or acclimation? For example, I just got back a couple of walnut logs I had taken to the sawmill and milled into a mixture of slabs, 4/4, and 6/4 lumber. Currently, that is sitting stacked and stickered inside a barn. But without a meter, how do I know when that wood is dry enough to move into the shop for acclimation and eventually for use? Everything I've read says you don't want to build furniture with wood that is above 7%-8% (actual value varies based on source). How do you know when wood has reached that level without a meter?

We're talking about something entirely different now, as Kevin pointed out above. In furniture making we're making design choices which allow for wood movement. It is typical that a few weeks are needed to acclimatize kiln dried stock to a shop, obviously depending on how thick it is. Generally speaking, the more the better and so many of us will buy stock far in advance of using it so that it is acclimatized without question.

If you are bent on buying a meter, buy one. I've got plenty of tools that are of limited use and when I use them, I'm happy I have them. That said you need to work on your designs.

A new woodworker is lucky to learn this lesson in a not so condemning fashion, but one significant enough to make certain you never make the mistake again.

[John TenEyck]

Sorry to read about your problems. Number one - stop listening to whoever told you to glue/nail your lumber to a plywood backing! Get a book or two on furniture design/construction. Also, just study existing pieces of furniture you already own, at the store, hotel you are staying at, etc. You can learn a lot about what works, and occasionally about what doesn't, by just being observant.

Do you need a moisture meter. No, of course not - but you should have one. I said of course not because people having been building furniture for thousands of years so it's certainly not a necessity. Furniture has been failing for just as long, too, so clearly lots of folks got some things wrong. Even now that we know everything there is to know about wood (not really) pieces still fail for one reason or another. So get yourself a moisture meter and learn how to use it and when to use. If you are going to buy green and/or air dried lumber I'd say it's a must if you want to know what's going on.

I mill a lot of my own lumber so I've seen how long it takes for wood to dry - using a moisture meter, and cutting then weighing and oven drying samples, too. Where I live in the NE 4/4 lumber cut in the Spring is down to 12 - 14% MC in 4 months; usually it wants to dry so fast I have to slow it down to avoid checks. If I cut it in the Fall it will take all Winter plus another 2 to 3 months in the Spring to dry the same amount. OK, fine, it's down to 12 - 14% so I can bring it inside. Uh, how long before I can work it you ask. Good question, and w/o a moisture meter you won't know unless you want to cut samples and weigh and oven dry them. I now have a kiln to finish drying my wood so I know it's 6 - 8%. Before I built the kiln I would check the lumber every week or two and plot the MC vs. the EMC in my shop, which I know from the RH meter hanging on the wall. When it gets within 2% I know I can use it. I still do that with lumber I buy.

I also use my moisture meter when I buy lumber. Just because someone says lumber is kiln dried doesn't tell you much unless you know the person telling you can be trusted. I've bought KD wood that turned out to be 12% moisture. It turned into a potato chip when I resawed it. That episode is what finally prompted me to spend the big bucks on a moisture meter - all $100 or so I think it was. People will spend hundreds or thousands of $'s to have an incrementally better piece of machinery but don't see the need to understand the MC of the wood they are running through those machines. To each their own.

You sound like someone who is eager to learn about wood working. Good on you. Learn as much as you can - including about the wood you are using. Buy a moisture meter. And buy Hoadley's book "Understanding Wood". Best $30 or so you'll ever spend on woodworking.

John

[JohnM Martin]

Thank you, John T. that was great.