Drying down stock blanks

[mnmuzzleloader]

I purchased a piece of black walnut that I cut up into 4 chunks that are roughly 35" long X 8" wide X 3 1/4" deep. On the outside of the wood the moisture measured 6-8%. When I cut the original larger piece into these 4 blanks the inside of the original piece is measuring 12%. I have read different things on the internet that say 12% is ideal to that it is way to wet. I have also read opinions that range from having the blanks kiln dried to not using any wood for gun stocks that has been kiln dried. I have the blanks in my basement with a dehumidifier blowing on them. I don't plan on using any of these blanks till next winter. Should I be having these kiln dried or should I just continue to air dry? Give me you thoughts.

 

[Col. Batguano]

Since you're in SW MN your wood will be pretty dry in the winter, and contain more moisture in the summer than if you lived in a more humid clime, like Florida. Wood will constantly be absorbing and outgassing throughout it's non living career.

As a rule of thumb, green wood cures at about 1" per year during air drying. If you force the moisture out of it through kiln drying, within a few years it will return to its' normal air dried equilibrium, but there will always be a disparity between the inside and the outside of the wood.

Your mortices like your barrel tang will be tighter in the winter than in the summer. I would suggest that you just seal the ends well to prevent checking, and let it do what it's going to do for the next year or so and then check it again before you are ready to work on it.

 

[Gustavo Hoefs]

I would cut the rough stock shape out a little bigger than needed and let it rest for while over the winter before carving it into the finished shape. lay it on some sticks or support it so it can allow any stress to relieve itself. I recently spent 30+ hours on a piece of cherry that surprised me and would now be perfect if I had severe scoliosis and was a left handed shooter.

 

[Rifleman1776]

The key is to not be in a hurry. I do some woodworking and am often given recently cut and milled slab wood. I seal the ends with Anchor Seal the stack and sticker them to lay flat. Then I forget for a couple years. Yes, years. :shocked2: I will say, 3 1/2" thick is pretty thick. Most slabs are 2 1/8" to 2 1/2" thick and, of course, dry faster. Main thing is to seal the ends, and be patient.

 

[eggwelder]

I make upper front hand guards for certain CF rifles. i have used kiln dried and air dried. air dried/seasoned i like better, i have a source for walnut that is seasoned over 30 years. i imagine it will make nice ML stocks as well.

 

[ohio ramrod]

I dry down my heavy planks (8 to 10 quarter) for three to five years in an unheated storage building and have no problems.I have found out from experience that 4 quarter kiln dried wood and air dried will have the same moisture content if left in stacks for a year or more. The kiln dried will reabsorb moisture while the air dried looses moisture to a point where the two become equal and then continue to change at the same rates as the air around them changes from winter to summer. :idunno: :idunno:

 

[Onojutta]

For comparison sake, dimensional lumber is dried to 15-19% moisture content. Some in the industry say that is on the wet side, even for lumber.

If you're at 12% now and won't be working it until next year you should be fine. The 6-8% you have on the outside is dry. Not going to get much dryer than that, even in the southwest.

Also, by the time you get the barrel inlet and the forestock roughed out, you will have a far cry from that 3.5" of wood. What's left will seek ambient much faster. I went long periods of time between working my current build and always left the barrel in the stock to keep it from warping, but again that forestock is so thin and flexible it would have to be significant deformation for that to cause trouble.

Lastly, shrinkage from wood drying is a much greater concern when the wood is restrained from movement, as in structural applications where the ends are fastened. A gunstock blank is not restrained from shrinkage as it dries, so if you are starting from 12%, any subtle changes that occur while it is being worked will be negligible.

 

[Col. Batguano]

Good post. Right you are about concerns over shrinkage. We're most concerned over wood wanting to shrink down and splitting because of the pressure against a non moving obstruction, like a metal inlay or something similar.

If we extrapolate the drying data further, and say wood will dry 1" per year that's approximately .02" per week. If you're like most of us, and take 3-6 months to do a build, in 3 months approximately 1/2" of wood thickness (because drying or absorption happens from both directions) will have reached ambient levels.

It would be interesting to know just how much pressure wood that wants to expand (but is restricted) can exert. And, the reverse. How much movement restriction will cause wood to split to relieve the stress.

 

[Onojutta]

It would be interesting to know just how much pressure wood that wants to expand (but is restricted) can exert. And, the reverse. How much movement restriction will cause wood to split to relieve the stress.

It can be calculated, but suffice to say it is tremendous. One of the first things I learned about the design of materials is that the natural forces of thermal expansion, shrinkage, etc. are too much to be resisted by any means and must be accommodated.

A colleague of mine, who is actually a structural engineer specializing in timber construction, recently told a story of a coffee table that he had built several years ago. Being new to furniture making, he had glued the top piece on all four sides and did not allow for expansion/contraction. A couple months later, he was sitting at his kitchen table and heard a series of loud bangs, which he thought was gunfire outside his house. He then discovered splits all throughout the top of his coffee table. The point of his story was actually to illustrate that the glue was so strong that the wood broke instead of the glued joints. But the fact that the splitting wood was so loud that he thought it was gunfire demonstrates the amount of stress that had built up in the wood. I have also seen 2x4 truss chords broken completely through their section as the result of being restrained at both ends. Imagine the tension force it takes to do that!

But again, this was because the wood was restrained against shrinkage as it dried, and is a much different scenario than what we have with a stock that is essentially free to shrink in all directions.

Agreed, the risk we have with our stocks would be any areas where the wood is trying to shrink around metal, such as inlays, the breech and tang, and barrel pins. But I am with you that in the OP's case, by the time he gets that far the wood will have reached ambient, and even if he didn't, I don't believe that starting 12% would be exceptionally problematic.

Lastly, in regards to the amount of movement it takes to relieve and accommodate the shrinking stress, it's actually very minimal. Wood is much more dimensionally stable in the direction of the grain than it is perpendicular to the grain. To use a 2x4 for example, it will expand and contract more in its width than it will in its length. In general, green wood shrinks only about 0.01% in the direction of grain. So for an 8' 2x4, that's only about 0.01". But, the shrinkage that is radial and tangential to the grain is many times more between 4-8% and this is where we have to be careful with the wood shrinking around imbedded metal.

Here is a website that provides some good basic discussion.
http://workshopcompanion.com/KnowHow/Design/Nature_of_Wood/2_Wood_Movement/2_Wood_Movement.htm