8/4" walnut question

[woodhick]

I have a load of 8/4" Walnut in the kiln now and looking for some advice.   I have dried Oak and Poplar but not any walnut before.   Kiln is a Nyle L200 in a tuck body, load is about 1500bd ft.   Running conditions set as a Goup 3.   I'm on day 3 and pulling off about 4% a day.  My main concern is before on poplar when drying 8/4" stock is getting the core dry at 6-7% also.   A lot of this wood will be resawn into thinner stock for the final product and I don't want to get it too dry on the outside and still wet on the inside if that makes sense?  Any input from anyone who routinely dries walnut 8/4"   Thanks.

[Den Socling]

I have never run a Nyle but I can offer some advice. I dry a lot of black walnut with thickness from 10/4 to 16/4 with vacuum kilns. When the outside of the wood is dryer than the inside, you are setting up a condition called case hardening. The good news is that walnut is tolerant to rough drying conditions. If you begin to case harden, you will see surface checks in most species. You will almost never see surface checks in walnut except for areas with crotch/feather grain. They are the prettiest and they will crack. Watch the figured wood.

[woodhick]

Thanks Den I know about casehardening and that is exactly what I'm trying to avoid.  Hoping some others here that have dried 8/4" material  in a Nyle would chime in.

[Kansas]

I gave up trying to dry 8/4 walnut and oak in our Nyle, at least putting it in fresh. For walnut and oak, we air dry for a considerable time, usually blocking wind and such and keeping it out of the sun. I'm not saying you can't do it, but it seems like you can't bring it down much faster in the kiln than air drying. We air dry for 8 months or so, then put it in the kiln. One time we tried a good sized load of 8/4 walnut. Outside of the boards tested 6%. Cutting the boards revealed 20+% moisture internally. We tried everything. I believe Nyle suggested spraying water in the kiln to bring moisture back up, we tried that. In the end, we unloaded it, let it air dry for some months, then put it back in.
It was a mess, and the quality was lousy in the end.

[Kelvin]

Call nyle and ask what they would do.  They had me turn the compressor off and run the temps at 150 degrees in the end to drive the moisture out of the core.  A moisture meter should read down to 3/4" deep so from both sides you should be getting the core moisture content.  Its hard to get the core the same.  Why bother to spend the extra time and energy, cost of drying them thick to saw later?  I'd saw to your size and then dry.  It will dry super quick that way and be even.  Really hard to make the core and exterior moisture the same.
KP

[Ironwood]

I always air dry my stock for a pretty long spell as well. Usually the turn around is a year or so.

              Ironwood

[woodhick]

Thanks for the replies guys.  I cut the stuff 8/4" mostly for leg stock for an upcoming woodworking club project that requires 8/4 squares for the turned legs.  Its a shearaton style table.   I mentioned resawing earlier as some people like to take the 8/4" and resaw and bookmatch for the top which is 4/4".    I am down to 68% mc by weight at this point.  Doesn't sound like anyone has had much sucess getting the core dry. I'll keep going and see what happens.  I will give Don a call at Nyle and see what he says.

[red oaks lumber]

won't tie my kiln up that long, airdry close to a year first.
like kelvin said resaw first dry last, don't bang your head on the door, open it much easier and doesn't hurt so much. lol
the best of education comes from the "board" of education
wishing you the best of luck with your load of 8/4 wood

[Ironwood]

I have no idea of the leg style you mentioned, but it might help if you could "core bore" the middle of the leg if it is to be turned fully. This would also prevent some radial checking if they are boxed heart.

          Ironwood

[beenthere]

I'd resaw when green, keep track of the pieces, dry as 4/4. and face glue to get the 8/4 stock for turning. Much less risk of honeycomb and/or collapse.

Are you taking test samples periodically to look for drying stresses at the surface of the wood?

[woodhick]

Well I'm stumped ???.   Surely we should be able to dry 8/4" wood.  I've read the dry kiln operators guide and followed along here for years so I understand all the mechanics of drying.  Commercial kiln dryers dry 8/4" wood and sell it all the time?   I have never resawed any and checked the core moisture content but I'm guessing its not a 10-20% difference like Kelvin is talking about in his post.   I mean there is a lot times 8/4" lumber is needed in  furniture making and if all I can dry is 4/4" I might as well sell the kiln and go back to air drying my lumber.   Would a convential style kiln be better for this instead of dehumidifier type?   
     Ironwood, this is small table with top about 14" square.  Legs are  1 1/4" square at the top where the apron/ drawer is and turned below.   Material will not be boxed  heart. 

[beenthere]

woodhick
Not that it is necessarily the same, but the walnut gun stock companies around St. Joe, MO used to dry gun stock blanks in large kilns for a 7 month stretch. That was in the 60's and 70's. There were a lot of efforts made to shorten that time. Dehumidification and vacuum drying were not being done at that time, I don't believe.

True, these blanks were highly figured grain in most cases. And they were worth a lot of money, so expensive drying may have been justified.

[Kansas]

I tend to think that dehumidifier kilns, while doing fine on thinner stock, aren't the best kiln for thick stock. That steady pull of moisture out is always pulling from the outside of the board. You can slow down how fast you pull out the moisture, but the outside is always ahead in terms of dryness. You also tend to lower the temperature to slow things down, and keep boards from staining, making it harder to get the moisture out of the core. A steam kiln can dry at a higher temperature, plus adding steam back can help equalize the board from time to time. I got to thinking back in our early days when we had solar kilns. A solar kiln works somewhat on the steam principle, in that you pull down during the day at a higher temp, and let the board equalize at night. Seems like we had a lot better luck on thick stock in the solar kilns. Towards the last times we used solar, we would put thick stock in the solar kiln, and then transfer to the dehumidifier kiln at the very end.

[red oaks lumber]

you can do that with d.h. just run the compressor less building up humidity in the chamber, it will give you a wicking affect pulling water from the core more to the surface, but it's going to take alot of time. i hope you have a snickers bar to eat!

[Den Socling]

Water always travels (diffuses in this case) from areas of high MC to low MC. The rate of diffusion increases with temperature. Even in vacuum kilns, I take walnut to a final temperature of 150 degrees.