What now? Cherry question

[woodhick]

I dried a load of cherry in my Nyle L200 kiln.  Everything seemed ok weight samples showed it at 6.8% moisture.   My moisture meter was giving the same results.  I cut a sample "fork" which showed no tension.   I sold a piece to a friend of mine and he calls last night and said he was having some pretty bad cupping when he resawed it to 1/4".  It was 4/4" to start with.   I checked moisture content on some of the boards stored in my shop and they read between 6 and 8%.  I cut a short piece off and resawed it in half.  Inside moisture is 14% .  Ok so now I know what the problem is but how do I correct it?  Can I put it back in the kiln and equalize it or condition it?  Thanks.

[SwampDonkey]

Even at 14 %, I wouldn't think there would be much shrinkage. I'm not a kiln man, just giving an opinion. Besides, it's not going to stay at 6 % for long when your EMC is closer to 14% anyway. But, I guess the cupping is from non uniformity in the drying. I'm wondering to if it's near pith or with partial sapwood on the boards. I had some cherry with boxed heart I bought a few years ago and it split all to pieces air drying.

[beenthere]

Your friend should have let the board set until the mc equalized before slicing into 1/4" thicknesses. Should be done as a general rule in wood working, I'd think.

Any idea how long the time was between end of the kiln run and when he sliced it ?

You might consider a longer equalizing period on subsequent runs, either in the kiln or at least on stickers in a somewhat controlled temp/humidity environment.

 

[woodhick]

Wood had only been out of the kiln for three weeks.  he did let it acclimate in his shop (humidity controlled) for a few days before he cut it.   I had some poplar and Pin cherry mixed in with the load of cherry (I know I'm not supposed to do that).  I cut a piece of both of them and they are fine   6-7% inside and out.  Just the black cherry is wet in the middle.  I have dried another load of poplar and basswod since that load, just finshed  four days ago.  I cut into them and they are fine   6-7% inside and out.   Not sure why the black cherry is so much different.   He had resawn the pieces to 1/4" thickness for his project. Width of the board he cut was 6" and it cupped about 3/16" over the 6".  Not a lot but still not flat enough.  also the board he chose was a  "sap" board.  By that I should explain that there was no white sapwood on the board but it was on that was cut farthest from the heart.  Hi picked that one because of the grain pattern.  I explained that it would be more apt to cup than a board that was more quarter or rift sawn.  I know all of those come into play but that still don't explain the moisture difference and why it's in the cherry and not in the poplar, or pin cherry that was dried in the same load.   Thanks.

[beenthere]

Takes longer for the moisture to move out of cherry than it does yellow poplar.

Now you know why they say "not supposed to do that"...

[woodhick]

Yeah I know that.  I did dry the load by setting the conditions for the cherry and not the others.  My sample board was cherry.  I know that schedule was slower for the poplar and I was runnig a chance of it staining but it didn't.   Can I put the cherry back in the kiln and "fix" it?  If so what should I set kiln settings at first? 

[woodmills1]

when he resawed he now had 2 boards wet on one side and dry on the other, no wonder they cupped.  don't know why the middle wasn't dry but do know why they cupped.

[SwampDonkey]

Yip!

And I don't know what effect juvenile wood (near the pith) will have either. I do know that when air drying hard maple that has any of that juvenile wood in the board, you might as well toss it in the firewood pile. I went through a lot of my barn dried wood of all species. And that hard maple with pith and juvenile knots all cupped to no use unless you want 2-3" molding wood.

[Justin L]

When the lumber gets down to 15-20%, I cut another moisture section to correct the MC of the sample(remember to reweigh the sample board after cutting off the section). For some reason, the calculated MC is slightly different than the actual MC after lots of moisture has been lost. After conditioning is done, I cut another sample to get the final MC.

You can also do a core/shell mc check by cutting a moisture section, then cutting off the outside 1/4" and weighing it. The cut out the center 1/4" and weight it. Dry them in the oven and weight each part again, you then have the MC of the shell vs the core.

If the shell is high, and you run the boards through the planer, the driest material is removed which raises the avg mc of the board. I have a Nyle 150(old:) so it only goes to 120deg using the compressor. The last couple % goes real slow at that temp(1/2%/ day or so) so I raise the temp up to 145deg to speed it up. The higher temp also helps even out the mc within the board. The last 3 days or so are at that high temp.

When it gets to 6%(the slowest drying sample-thick, rift/qtrd heartwood)  I raise the humidity to about 87% @ 140deg to condition it for 12-24hrs to relieve stress.

[woodhick]

thanks Justin.  How do you riase the humidity at the end if it is lower than the 80% or so.  I have heard of people spraying the wood with water to wet the surface.  I have no way in place yet to add steam or moisture back into the kiln.  thanks..

[Justin L]

It takes 10-15 gallons per 1000BF to keep the humidity that high at that high of a temp. (Maybe less if your kiln is REALLY tight)  I use an airless sprayer pump hooked up to a mist spray line I bought from Kilndirect.com. It's a stainles steel line with 8 spray nozzles that create a fine mist @ approx 800psi. It doesn't look like the way the do it in the city, but it works out here where I'm at I think four nozzles may have been enough.

Since I don't have a well close to my kiln, I save the condensed water in a 65 gallon tank, using a sump pump to get it into the top of the tank. The tank is also in the kiln chamber so it is somewhat hot when it gets sprayed.