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Cupped cherry slabs from solar kiln

Started by Glenn1, January 01, 2018, 08:39:29 PM

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Glenn1

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?
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

maderahardwoods


Don P

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.

WDH

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. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

YellowHammer

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.

YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

Glenn1

Thank you for your responses.  I'll remember to air dry it first the next time I have cherry slabs.
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

YellowHammer

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? 
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

GeneWengert-WoodDoc

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.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Glenn1

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.
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

Glenn1

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.
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

YellowHammer

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.   
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

Ianab

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.
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

GeneWengert-WoodDoc

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.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

WDH

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. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

Glenn1

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. 
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

GeneWengert-WoodDoc

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.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

moodnacreek

I you think cherry is bad try elm.  Overhung first and last  stickers and tons of weight helps.

YellowHammer

YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

GeneWengert-WoodDoc

Sweet gum (Sap gum and red gum) and cottonwood are just as bad as elm....maybe sweet gum is worse.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

moodnacreek

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?

ellmoe

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.
Thirty plus years in the sawmill/millwork business. A sore back and arthritic fingers to prove it!

WDH

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.
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

moodnacreek

Ellmoe, that sounds like 'red birch' up north that is actually the red heart wood of white birch.         Thanks

pineywoods

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..
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

YellowHammer

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
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

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