Eastern Red Cedar stability issues

JamieK · March 21, 2024, 10:34:21 AM

Hey guys, I sell alot of Eastern Red Cedar and I normally allow the lumber to air dry. A customer approached me with a purchase of 500 bf milled at 11/16" thick and 6" wide. He needed it in a few days so I told him I would put it in my kiln and dry it down to 15% which I thought was in the stable range for this lumber. He took it home then planed it to 7/16" thick and ripped them into multiple width boards then stacked and stickered them in his shop. After a couple days in his shop they dried down to 6% and most of the boards bowed and crooked on him. Should I have dried these down further or was it because of it being in the kiln that added the stress? They were in the kiln for 3 days at 80°f.
Any help is greatly appreciated.
Jamie

doc henderson · March 21, 2024, 11:39:18 AM

ERC is usually pretty forgiving. did you see if he stickered them well?

JamieK · March 21, 2024, 11:57:06 AM

I'm not sure of how he stickered them.
Now he wants to try this again but he wants me to dry them down to 6%. I believe Gene has said the best is 9.5%. If i dry down to 6% what condition will that lumber be in as far as planing?
My customer has a lumber professional that suggested 6% them equalizing

Larry · March 21, 2024, 12:08:32 PM

Going from 15 to 6 percent is a big change. I would expect lots of movement. Your customer should have brought the lumber home, stickered it to bring it to the desired moisture content, and than machined it. IMO 6 percent is too dry (unless flooring) both for use and machining. In a conditioned house in my area the EMC is going to be right at 8%.

Lumber always shows some movement after machining as stresses are relived in the board. Most of the time it is very minimal and has no effect. If it has to be perfect, I mill close to the final dimension than let it acclimate in the shop for a couple of days and re-machine.

CCCLLC · March 21, 2024, 03:59:31 PM

I believe in what Gene has mentioned. Can't believe he got them down to 6%, without the possibility of a kiln being involved. Air drying usually stops at best, @ 9.5%.

doc henderson · March 21, 2024, 04:17:43 PM

he planed them and then put them in his shop. if it is a conditioned space, it could get to 7%, but not in three days, although it is planed thin. I assume he had fans on it. I can get maple at 5/16th down to 6 to 8% in 4 days in my shop, with a fan 24/7, but that is stickered every 8 inches. I expect losses that thin.

the top photo is after it dried, and the bottom is now. some of the sap wood got a curl in it in two of the center sheets. the rest looks good. this will be planed (to see if the spiral does a better job) and or drum sanded to about 1/8th inch.

the middle is today on the front side or back from the fan. pretty dang straight. I might try turning the stack daily like reversing fans in a kiln. big stuff!

doc henderson · March 21, 2024, 04:37:36 PM

update, current MC 5.8 to 6.2%. the straight blade planer would chip these into oblivion at a thinness I am trying for. the drum sander takes some time but works well.

JamieK · March 22, 2024, 08:21:07 AM

I'm doing an experiment now with four boards. I just started a kiln load so I put the four boards on top of the stack, strapped down. When 2 of them reach the 9% I will take them out and perform the same machining he did. Then when the last 2 reach 6% I will do the same

jimF · March 24, 2024, 08:18:21 AM

Did the movement occurre during the machining or over a time period. if during machining it was caused by drying stresses. If over time, it was because of loss of moisture and the boards were not dried enough.

JamieK · March 24, 2024, 01:23:49 PM

The movement happened after machining. When the moisture went down to 6%. My big question about all this is that i thought erc was stable at 15%. I obviously was incorrect. Right now the erc that is in the kiln is at 16%. It should only be a couple more days to get to 9%

doc henderson · March 24, 2024, 02:02:23 PM

I think the question is, did the movement occur as you were milling (immediate) or in a few days. the first is tension release and the second can be drying stress.

jimF · March 29, 2024, 02:27:58 PM

When I first read Doc's reply I wondered why he repeated what I said and just passed it off. Last night I could not sleep while waiting for a medical procedure in the morning and all the different explanations different doctors and nurses gave me for the problem caused nothing but confusion because they never got to the true explanation and remembered how Doc reworded my reply and realized both of us did not get to the true accurate explanation.. So now that I have to rest from the procedure here goes with a detailed accurate explanation.
All easily observable movement in wood is caused by elastic stresses; meaning a stress like pulling a rubber band or spring and when that stress is removed the object springs back. And these elastic stresses are caused by loss of moisture because loss of moisture is a loss of volume resulting in wood shrinkage..
After typically drying process we will assume the moisture content is consistent through the board when the drying is finished. The full drying process causes the board to end up with the surface in compression and the core in tension. Because the two surfaces in compression equals the tension in the core. Since the stresses are balanced there no movement until the board is ripped in thickness. The stresses are not balanced and being the stresses are elastic there is an immediate movement. And the blade is pinched and stays that way.
Now lets assume another board was not finished drying and the center has a high moisture content but the stresses are low or non-existent. When it is ripped like the previous board the stresses are balanced and no immediate movement. But as time goes on the higher moisture content in both half board now starts drying causing unbalanced stresses causing slow movement (cupping and bowing), say over night.
Now a third board is also not finished drying so the center of the board has higher moisture content. You put it through a planner and removed both dry surfaces. It's now at the desire thickness and it is the end of a work day so you placed it on a bench over night. When you come in the next morning the board is bowed and you cannot joint it flat because because it is down to thickness. What happened? The surface of the board was exposed to the air dried and shrank while the other surface was not exposed and did not dry and or shrink. The board will flatten a little as it finishes drying but not completely flat causing problems if the board was intended for a floating stile or door jamb.
Now one for you to figure out. A very thin board is green is cut in a sunny breezy morning is placed on the ground or a bench in the ; in the afternoon you come back and it is distorted. The cross-section shows the edges of the board are flat but tilted up at the edge., te center of the cross-section is strongly cupped in the same direction, somewhat resembling a flying bird head on. On top of this the length of the board is bowed in the opposite direction. How did this happen? Hint the board is cut from a plantation grown tree.

doc henderson · March 29, 2024, 08:11:25 PM

nice examples Jim. I was asking the OP @JamieK as he said after milling but did not specify immediate vs a few days later.

JamieK · April 01, 2024, 11:18:12 AM

I removed one of the boards. It was 9.5% moisture and it had a 7/8" crook to it. I cut it in half length wise then planed and straightened one edge. It machined very nicely with no chipping. Then i tried to rip it into 2" strips and it was moving like crazy as it was going through the tablesaw. Then i cut strips 2 1/2" wide to try and sneak up on the 2" width. Even when i cut only a 1/16" off it would move about 1/16" . Any ideas?

doc henderson · April 01, 2024, 12:18:01 PM

It sounds like stress in the wood. I wish I had a great answer. Not sure if a conditioning would help. to be scientific you could do a prong test. but I think if it moves as you cut, it is not further drying stress, but intrinsic stress. the MC was that a pin or pinless meter? can you check surface vs core moisture? although it sounds like stress in the wood. are these 4/4 boards? sorry if this has been answered. I mistreat the crap out of my ERC, and it rarely gives me any trouble. I airdry then bring in the conditioned shop.

Larry · April 01, 2024, 03:15:45 PM

When you said the board has 7/8" crook that suggests the board is vertical grain. When I think vertical grain I see juvenile wood on one edge of the board. Juvenile wood gets its name because it "misbehaves". Saw the juvenile wood off one side and stress is relieved causing more crook.

ERC is known to have a few knots which can also make a board warp.

I'm just guessing based on some of my experiences.

beenthere · April 01, 2024, 05:39:52 PM

Pics of the grain in these boards would help further diagnosis.

scsmith42 · April 02, 2024, 07:19:33 PM

How are you measuring the MC%? Pin type meter, pinless or oven-dry method?

In pin type, are you taking readings at both the shell and the core of the boards? If so, what is the delta?

jimF · April 05, 2024, 07:20:28 AM

Conditioning is effective for both transverse (cupping) longitudinal ( crook & bow) drying stresses but is definitely more so for transverse. For conditioning to be effective the lumber needs to be at the elevated temperatures, or higher, it experienced during drying, to be at the high stress level it was in and for the moisture gain to be fast. Eastern red cedar usually has very wild grain patterns due to knots and possibly juvenile wood. After ripping, relieving much of the stresses I don't think conditioning would help at this point. I think you have what you will get and try using what you have for short pieces where crook would be less noticeable.

Speaking of juvenile wood (hint!), has anyone tried figuring out the last example of drying stresses?

JamieK · April 05, 2024, 09:46:22 AM

Well the last three boards are out. Pretty much all of the boards were vertical grain but just above the pith. This is probably why I was getting these issues.At the end of the kiln cycle I did a conditioning of the load. The three boards when I took them out, had the crook to them that the first board had a few days earlier. When I planed them, they were very nice with no brittleness. I cut the boards in half length wise to minimize loss from the crook, then ripped them to 2 1/2" wide. All of the boards stayed nice and straight except for one.

JamieK · April 05, 2024, 09:50:03 AM

The meter I use is the Lignomat VersaTec

doc henderson · April 05, 2024, 10:14:52 AM

thanks for sharing your experience so we can all continue to study these issues.

JamieK · April 05, 2024, 06:57:13 PM

When I conditioned the load it was at the tail end of the sterilization phase 145°. How I do it is I open the door and stick the wand of my pressure washer in and blast it until the emc is where I want it. It works very nicely.

jimF · April 15, 2024, 07:31:48 AM

I see no one tried to explain the last example " A very thin board is green is cut in a sunny breezy morning is placed on the ground or a bench in the ; in the afternoon you come back and it is distorted. The cross-section shows the edges of the board are flat but tilted up at the edge., the center of the cross-section is strongly cupped in the same direction, somewhat resembling a flying bird head on. On top of this the length of the board is bowed in the opposite direction. Hint the board is cut from a plantation grown tree. "
The answer lies in the board being thin and it being plantation grown. Leaving it in the sun on a breezy day caused fast drying on one side causing it to bow up from shrinkage stresses. With it being plantation grown it contains juvenile reaction wood in the center which shrinks more than normal wood in the longitudinal direction.This large shrinkage in the longitudinal direction reduced as you progress away from the pith. With the board already bowed the short length in the center increases the bow because the inside of a curve has a shorter length than the outside of a curve. Also, this decreasing shrinkage of the juvenile wood causes the cupping in the transverse direction. On the edges it contains normal wood which has uniform and less shrinkage in the longitudinal direction causing the straight "wing" portion.
I've seen this occur to someone using a portable band saw and it has been a dramatic and wonderful example of the result of different shrinkage rates within one board.