Drying slab question

What type Meter?

Mark Mandell - Gone Round In New Jersey

Pin-types don't (usually) read very deep. Pinless like my Electrophysics, can read an inch into the wood to get you to the center.

Personally I'd let it sit, with weight on, until you get 11% out of the center.

What's the rush?

Re: Drying slab question

JL

The answer is - it depends.

What do you want to do w/ the slabs?

Sweetgum (in my experience) can be a PITA to work. The grain is sort of "squirrelly" in my opinion as it is interlocking. I would want it to be drier before I planed it - but that's me. YMMV.

That being said, I like working w/ it when it is somewhat green. It responds reasonably well to a sharp draw knife and spoke shave. You can rough shape it w/ a band saw and get some really nice curves. It will steam bend moderately well.

you left out important info

John K Jordan

>>>I bought a couple of slabs of Sweet Gum. Green as grass. What MC should i go for before starting to clean them up. They are about 18% now according to my meter. They are about two inches thick and I would like to thin them down.

Are they stacked and stickered inside or outside? Wood will eventually reach EMC for that environment. If outside, the environment depends on the area you live in, the time of year, and the local weather variations. Here is a partial chart from a government publication for typical EMC for wood outside, whether stickered and covered or on a shed or covered porch.

If indoors, the final EMC depends on the temperature and relative humidity and the consistency in the building. In my shop without extreme heating (I keep the thermostat between 62-68F in the winter and 75-80 in the summer) wood dries to about 10-11%. A 2x2" turning blank can be dry in months since moisture can easily escape from all four sides. A wider plank or slab will take much longer depending on the species. It might take as long as two or three years.

I use a pinless Wagner moisture meter to give me an idea of the current MC. It claims to read at least 3/4" into the board. Keep in mind the moisture gradient in the board can mean the outside surface might be much dryer than the center, especially at first, less as it approaches EMC.

The oven dry method of testing will give you the absolute moisture content but is a destructive method requiring you to cut a sample from near the center of the slab.

The weight monitoring method is non-destructive and depends mostly on the precision of your scale and how careful you are at weighing. For most turning blanks I use a scale good to a few grams. If you have a scale capable of weighing your slab, perhaps standing on end on a bathroom scale, weigh the slab and write the weight and date on a piece of tape or sticker on the board. Weigh again each month or so, longer if your scale has the low precision typical of an inexpensive scale. Make sure the slab is resting on the scale and supported the same way each time. When the weight doesn't significantly change over two or three weighings the wood has reached EMC. Note that due to the changing seasons, the weight can actually go up if the humidity and temperature changes with the season or weather.

Note that like other lumber, the amount a slab will warp depends on several things including the species. Assuming straight grain and the absence of significant reaction wood, one of the most important things is the orientation of the wood when it was in the tree, i.e., the the angles and position of the log on the sawmill relative to the grain and the pith. Years ago I did a study and both surprised and convinced myself of the basic importance of that.

If weighing and tracking is too much trouble, just sticker, stack, and weight the slabs and forget about the wood for at least three years. Wood such as sweet gum is likely to dry much quicker than that but don't take my word for it.

JKJ

Re: Drying slab question

Larry Barrett

As JL says, it depends. I think it depends on what your final thickness plan is. You say it is about 2" now. If you want it to finish at 1 7/8" then you need to wait. But if you want it to finish at 1" or 1 1/4" then there is no reason to not run it through a planner to clean it up. Running wood at 18% or even higher through a planner is easier on the planner than running dry wood through. In my experience the moisture does no damage to the planner knives but might leave a little gunk.

Hoadley's book Understanding Wood has a chart that shows the expected shrinkage for various kinds of wood as the moisture content goes from green (20% or higher) to oven dry. The shrinkage is reasonably linear across this range. For Sweetgum, the tangential shrinkage is 10.2%, and the radial shrinkage is 5.3%. My experience with oak is that these numbers are on the high side (expect less).

If you do run it through a planner, take same amount off both sides.

Re: Drying slab question

Barry Irby

The meter is an Accuscan pinless meter. For the life of me I can't think of the name brand.

These two planks are about 20" wide and near six feet long.

I plan to hang them on two verticals to make the head board and foot board of a bed.

I have been weighing them about every two weeks. They started out near 70 lbs and are down to about 57. I am weighing them on a package scale that only has half pound increments. They are standing upright in a conditioned space. l will continue to weigh and watch. Was just thinking I might accelerate this by thinning them down a bit. OTOH, I may need the thickness to flatten them.