Hello all,
This summer, we cut about 600 bf of 9/4 cherry slabs. I've been drying with my Nyle kiln for 2 years now so I didn't expect any problems. I left the slabs in the kiln for 5 months and they may have left them in longer than necessary. The solar kiln is not kept on my property as we have too many trees. The cherry slabs came out cupped. We also had some 9/4 walnut and they came out perfect. Does anyone have a possible explanation?
Do you have the slabs weighed down?
My experience with cherry is that it does like to cup while drying but is pretty stable once it gets there. Walnut is more like white pine during drying, it just lays there.
I find cherry tough to dry without defect. Also, if there is sapwood on one side, I get really bad bow. One of the worst woods for me for cracking and checking and splitting. It ALWAYS pith cracks very badly. I do best when it is air dried to less than 20% before finishing it off in the kiln.
WDH beat me to it.....How much sapwood? Was it balanced on each face? Sapwood "pull" is real bad on cherry, and can really be aggravated once the wood gets below 7%. Pith cracks also cause a lot of cup on cherry.
(https://forestryforum.com/gallery/albums/userpics/21488/IMG_4332.jpg?easyrotate_cache=1511961455)
Thank you for your responses. I'll remember to air dry it first the next time I have cherry slabs.
Put all the weight you can on it, even hen solar kiln or air drying. It won't stop all cup, but it certainly helps. Didn't you make some concrete slab weights?
Cupping is a natural tendency of flatsawn wood. It results because the bark side shrinks more than the heart side...sometimes 25% more.
Cupping is worse when we dry slowly. In air drying, the outer cells get drier than in a kiln, so they are stronger and resist warp. Oftentimes in the kiln we use a high humidity (higher than the 65% average humidity in air drying) which prevents the outer cells from getting very dry and not much stronger.
If we rewet partly dried lumber, cup will be worse. Never allow partly dried lumber to get rewetted.
Cupping is worse as the lumber gets drier.
Cupping is slightly worse if it does not have weights, but not much.
Quartersawn, perfectly Quartersawn, does not cup.
Cupping is worse as the flatsawn lumber is sawn from closer to the pith. This means small logs will have more cupped lumber. Logs that do not have a large tie or cant from the center will have more cup. This means lower grade lumber will cup more, as most low grade comes from near the center of the log.
Quote from: YellowHammer on January 02, 2018, 11:00:12 PM
Put all the weight you can on it, even hen solar kiln or air drying. It won't stop all cup, but it certainly helps. Didn't you make some concrete slab weights?
Yes, I have four 4'x4' slabs that weight 1000 lbs each. My solar kiln is 20 Miles from our farm and I've been using the concrete in the DH kiln and on a stack of air dried wood. I could use more of them.
Quote from: GeneWengert-WoodDoc on January 03, 2018, 07:05:45 AM
Cupping is a natural tendency of flatsawn wood. It results because the bark side shrinks more than the heart side...sometimes 25% more.
Cupping is worse when we dry slowly. In air drying, the outer cells get drier than in a kiln, so they are stronger and resist warp. Oftentimes in the kiln we use a high humidity (higher than the 65% average humidity in air drying) which prevents the outer cells from getting very dry and not much stronger.
If we rewet partly dried lumber, cup will be worse. Never allow partly dried lumber to get rewetted.
Cupping is worse as the lumber gets drier.
Cupping is slightly worse if it does not have weights, but not much.
Quartersawn, perfectly Quartersawn, does not cup.
Cupping is worse as the flatsawn lumber is sawn from closer to the pith. This means small logs will have more cupped lumber. Logs that do not have a large tie or cant from the center will have more cup. This means lower grade lumber will cup more, as most low grade comes from near the center of the log.
If this is the case, then what are the advantages to using a solar kiln? I've been air drying my wood for a couple of years and then putting it into the DH when mc is around 20%. It has worked well for me. I built the solar kiln for live edge 9/4 slabs. Since slabs have sap and a pith, is cupping going to be a problem with other woods? It did not seem to affect the LE walnut.
I've been drying 9/4 in my solar kiln almost exclusively for years now. About a dozen species. Cherry is the worst to cup, seems like, for example that photo I took was of an air dried stack, and you can see how bad the sapwood cupped.
The solar kiln seems to do a very good job and is noticeably faster than air drying and seems keep the defects level low. I never noticed any unusual increase in cup. Unfortunately I don't track the atmospheric data in the solar kiln. However, I don't let I'd get very moist, I like a low and dry heat.
QuoteIf this is the case, then what are the advantages to using a solar kiln?
Cutting 21 months off your drying time is a pretty big advantage, while the setup and running costs of a solar kiln are relatively low compared to other kiln styles.
And some species of wood are just a pain to dry, no matter what method you use.
Good ol' YH knows what he is talking about for sure. If you read what I wrote, note that it is high humidity that results in more cup, so (as YH says) keeping a solar kiln as dry as possible without causing checking is perfect. But, this low RH cannot be done with all species...it would ruin oak. We would have to be careful with walnut to avoid end slits and honeycomb.
Again, the sawing technique has a great influence on cupping, as mentioned. So does small logs. Etc.
It is next to impossible to dry a piece flat that contains the pith.
The pith in cherry is a major issue. The juvenile wood cracks and splits as bad as any species that I have dealt with. One of the worst.
Quote from: YellowHammer on January 03, 2018, 10:46:08 PM
I've been drying 9/4 in my solar kiln almost exclusively for years now. About a dozen species. Cherry is the worst to cup, seems like, for example that photo I took was of an air dried stack, and you can see how bad the sapwood cupped.
The solar kiln seems to do a very good job and is noticeably faster than air drying and seems keep the defects level low. I never noticed any unusual increase in cup. Unfortunately I don't track the atmospheric data in the solar kiln. However, I don't let I'd get very moist, I like a low and dry heat.
YH, I'm intrigued about having the kiln use "dry heat". So here's a scenario. It's July and you just put in a load of slabs. Humidity and heat are very high. Using the vents, how do you avoid the hot moist heat. This is assuming that you did not put a DH unit in the solar kiln.
The average humidity in the summer in most of the USA and Canada is 65% RH average...drier in the afternoon and more humid in the early morning. Also, the humidity is a bit drier on a sunny day and a bit higher on a cloudy day. This is around 12% EMC, which is considered a fairly dry condition. So, if a solar kiln is run with the vents wide open and with no solar input, the conditions in the kiln will be quite dry indeed. To help, the fans should be run only during the daytime, avoiding the very high humidity before sunrise.
Now, add the solar heat, and the humidity in the kiln will be even lower. Maybe too low.
So, we partially close the vents and allow some of the evaporated moisture from the lumber to stay in the kiln and increase the humidity. Theoretically, we can keep the vents closed and achieve 100% RH even with solar heat, so we would get no drying at all. Practically, there are leaks in the kiln, so it is never 100% sealed.
So, a solar kiln when the wood is fairly wet can essentially run at humidities between about 50% RH to 100% RH. The vent operation, and how well sealed the kiln is, determine if the solar kiln has the desired RH average.
I you think cherry is bad try elm. Overhung first and last stickers and tons of weight helps.
Glenn1, what Doc said smiley_thumbsup
Sweet gum (Sap gum and red gum) and cottonwood are just as bad as elm....maybe sweet gum is worse.
Wouldn't know sweet gum or sap gum if I cut one down. Our cotton wood is quaking aspen and it does go nuts. Is red gum what we call Pepperidge with spiral grain?
Quote from: moodnacreek on January 07, 2018, 05:54:00 PM
Wouldn't know sweet gum or sap gum if I cut one down. Our cotton wood is quaking aspen and it does go nuts. Is red gum what we call Pepperidge with spiral grain?
Sap gum and red gum are the sap wood and heart wood of a sweet gum , respectively. Red gum is very attractive while the sap gum is just off white and not very interesting. The sap gum is very attractive when spalted, however.
It takes an old sweetgum log to develop that beautiful heartwood. Growth stress like competition or poor site slows growth and can trigger heartwood formation. I plan to harvest a big ole sweetgum and quartersaw it in a few weeks.
Ellmoe, that sounds like 'red birch' up north that is actually the red heart wood of white birch. Thanks
Quote from: WDH on January 08, 2018, 07:46:55 AM
It takes an old sweetgum log to develop that beautiful heartwood. Growth stress like competition or poor site slows growth and can trigger heartwood formation. I plan to harvest a big ole sweetgum and quartersaw it in a few weeks.
Reverse roll QS sweetgum ? sounds interesting.. Pics please..
Quote from: pineywoods on January 08, 2018, 10:14:29 AM
Quote from: WDH on January 08, 2018, 07:46:55 AM
It takes an old sweetgum log to develop that beautiful heartwood. Growth stress like competition or poor site slows growth and can trigger heartwood formation. I plan to harvest a big ole sweetgum and quartersaw it in a few weeks.
Reverse roll QS sweetgum ? sounds interesting.. Pics please..
I'm interested to see how it looks, also. Historically, I would forward roll sweetgum into the nearest burn pile :D :D
Speaking of cottonwood, 3rd or 4th log/tree I sawed on my mill was a big old cottonwood that I had to trim the butt log with a chainsaw to make it fit the mill. Slabbed it at 6/4, put it on sticks and let it air dry. Cupped something aweful. I thought about putting in back on the mill to flatten it but there wouldn't be anything left. So it's been sitting there. About a year ago I took the cover off to use it to cover some good wood and I noticed the other day that it is starting to flatten out. Don't know why it's flattening but I think one of these days soon, I'll have to check it out. With no cover, it may be rotten, had a very wet spring.
Quote from: WDH on January 08, 2018, 07:46:55 AM
It takes an old sweetgum log to develop that beautiful heartwood. Growth stress like competition or poor site slows growth and can trigger heartwood formation. I plan to harvest a big ole sweetgum and quartersaw it in a few weeks.
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I seen 12 - 14" dbh sweet gum that was heart, "wall to wall", and 30" with no heart at all. Not knowing where or under what conditions they came from, I assumed it to be growth and stress related.
Appreciate that sapwood in cottonwood dries really fast. The heartwood which often has bacterial infection will be around 140% MC and will dry very slowly with bacteria, taking months and months. This is worse with thicker. So the sapwood will shrink and cup. But then as the heartwood dries later and shrinks, the cup will decrease. Unfortunately, it is not likely to flatten perfectly.
Quote from: YellowHammer on January 02, 2018, 11:00:12 PMPut all the weight you can on it, even hen solar kiln or air drying. It won't stop all cup, but it certainly helps. Didn't you make some concrete slab weights?
Yellow, I need to get some more weights and saw this about "concrete slab weights". Seen any posts or details here on ones that are practical and reasonable to make?
Not really using much concrete for weight anymore, I've switched over to using marble and granite slabs for weights.
I was using a concrete septic tank lid.
Yellowhammer
That's a crappy weight to use!! :D
:D :D :D
For some reason all my wood had a peculiar odor.....
Quote from: YellowHammer on May 23, 2018, 10:41:35 PMNot really using much concrete for weight anymore, I've switched over to using marble and granite slabs for weights.
Interestesting. Did you make a "bin" or pallet with them attached? I have been considering building a pallet with cement blocks strapped down to it. Another item on the ever-growing task list.
I thought it was just all about sawing logs. :D
I use a pallet with a layer of cement blocks as a weight.
Just an 8 foot long oak pallet, top and bottom decking screwed on, and stacks of flat rocks. I believe about 3,500 lbs.
Quote from: WDH on May 25, 2018, 07:21:01 AMI use a pallet with a layer of cement blocks as a weight.
I was thinking of doing the same. Yellow's granite is pretty cool. Thanks.