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If the equalibrium moisture content in my region is 12.5 to 15%, what is the necessary / recommended MC for black walnut as used to make kitchen raised panel doors as well as furniture?
I am afraid there is really no simple answer to this
question. But an answer is available and it is found at
You must consider the area you live in and
the conditions in which your project will be installed. In the case of raised
panels enough space within the rails and stiles is needed to allow for panel expansion
and contraction. Also DO NOT GLUE the panels in place under any conditions for
they will split.
Available are special balls to remove the “rattle” out of a
raised panel door. These I would highly recommend no matter where you live. One
place where they can be found is woodworker’s supply, http://www.woodworker.com
#112-697 bag of 100 for $4.79
Hope this Helps
The WEB site in my last reply to Jeff Allan post should be as follows:
Thanks for the reply. I will play it safe and arrange to kiln dry the lumber to around 8% for optimum stability.
Kiln drying is not always the best option. When lumber is kiln dried it becomes case hardened. That is the exterior of the board is dried quickly while the interior remains at a higher moisture level. This causes greater stresses on the outer surfaces of the board which don't tend to manifest themselves until the board is worked. Even though it is kilned dried, that does not mean it qualifies to meet the levels of moisture content for your area of the country.
To give you an example of this, when some kiln dried boards are run through the table saw you will notice that the board will either pull away from the saw's fence or pinch off the blade even though saw may be set up correctly. Then after the board is cut it can spring into an arc or twist laterally. This is all due to stresses within the lumber.
The alternative to the kiln is of course air drying. Properly air dried lumber, machines without any problems and stays put after the cut. Of course you can't buy air dried lumber from lumber yards or board stores. You pretty much have to get it directly from saw mills. Then once you get it, it needs to be stacked, using sticks, under cover and out of the weather. It then must be allowed to dry over time until it reaches the ambient moisture content of the region in which you live. This is usually about a year. The best way to measure and determine the actual level of moisture is with a moisture meter.
I know this really doesn't solve your immediate problems but I hope it gives you a better insight into what your up against. For your current problem dealing with the Walnut, I would recommend purchasing the walnut you will need and then stacking it (with sticks) in your home. Then using a moisture meter, measure the moisture content of the solid wood furniture (not Plywood or MDF board) within the home to establish a target level for the walnut. When it reaches that level, build the project.
Thank you for your answers. Much appreciated.
What sort of tolerances are acceptable? Flat sawn walnut only shrinks about 2.3% (about 1/4" per ft) across the grain and .25% (about 1/32" per ft) lengthwise when it goes from 15% (air dry) to 7% (kiln dry). Since the frames run lengthwise and the panels are designed to "float" in them, building with air dry lumber won't cause a problem, if you build them tight. That's the reason for the panel construction-- back in the old days, they didn't have the luxury of kilns, and found ways to allow the wood to move. Calculations, by the way, come from the shrinkage calculator on Woodweb.com.
MinnWorker, your description of case hardening is accurate, but it should not be accepted as a property of kiln dry wood. The big kilns push the wood through as fast as they can and rushing the kiln schedule to can cause a host of problems, such as case hardening. I run a custom band saw mill and work with all types of Ozark hardwoods, including walnut, oak, hickory, ash, sassafras, sycamore, cherry, ash, maple, eastern red cedar, and hedge (Osage orange). If a customer wants kiln dry wood, I take it to a local kiln that does custom drying, and have never had any problem with case hardening.
Kiln drying at a slower pace and allowing the wood to equalize moisture content between the core and the surfaces will give excellent results. If drying wood in the shop, end sealing the boards with a product such as Anchorseal will go a long ways toward preventing end checking. Run fans to blow air across the stack during the day, and shut off the fans at night to let the boards equalize,and you'll speed things up without compromising the quality of the lumber.