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Is it possible to screw up red Oak with an MC of <15%?

Started by oakiemac, July 30, 2005, 04:53:02 PM

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oakiemac

I just pulled a load of Red Oak out of the Nyle L200 and noticed that a lotof the lumber had honeycombed and checked on the surface of the boards. I had about 1500bf in the kiln and it had air dried for about 5 months, mc was 12-15%. The load was only in about 5 days and came out with an average mc of 7%. I had the temperature set at 120 F, and comperessor duty cycle at initially 90% then I lowered it after 2 days to 65%.
This is only 2nd load through my Nyle so I'm not quite used to it yet but I didn't think I could screw this up since the MC was already less then 20%. The oak could of had these problems before it went into kiln but I didn't notice them. I have never had this problem before, either air drying or kiln drying with the Ebac.
The Ebac dries at a much slower rate and maybe that helps make it idiot proof. Any ideas from you guys with more experience?
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

Den Socling

Did you cut samples and bake pieces from the core before they went into the kiln? My first guess would be that the core was still above 28%.

oakiemac

No, all readings were taken with a pin type meter. I doubt that the core mc was that high. this oak had been sawn in february and has been air drying since then.

Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

Den Socling

This might sound like a dumb question but are you sure it was all Red Oak?

I recently dried a couple loads of 8/4 Red Oak flitches. The first load was good at 9 days and I pushed the second load to 7 days. I was shocked when I found about half the flitches in the second load with deep surface checks. Then I ran a couple of the cracked pieces through the planer and discovered they were White Oak. I had to get real close to these big, heavy buggers to get them loaded and I never noticed that they were White Oak until I planed them and saw the length of the rays. The core of WO stays a whole lot wetter than the core of RO.

In short, if the oak was 12-15% throughout, you can't get new checks (internal or external) after putting it in any kiln. How deep did your pins reach?

oakiemac

Den,

The wood is definately red oak. Strangely enough, I did have 100bf of quater sawn white Oak in the kiln as well and it all turned out good.
I'm thinking that the defects that I saw must of happened during air drying. You confirmed my suspicions when you said that you can't get checks at 15%mc. That is what I thought but I just wanted to make sure.
I used a Delmhorst j-2000 with pins that are rated for 6/4 lumber. I usually check several boards at the ends and on the edges. I guess I never check at the surface of the board because of the pin marks that are left.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

Den Socling

The J2000 will give you good readings but you need to stick the center of the board. Ends and edges dry rapidly. I know what you mean about the holes. They can be forgotten in rough cut but I hate it when a perfect board comes out of the planer with a snake bite in the middle.  :(

Did the WO have the same air-time?

Don_Lewis

Honeycomb is always caused when the lumber is over 25-28%. You don't necesarily see it unitil it is dry. It wouldn't have mattered how fast you dry it. I think you should probably look at how you air dry if you are sure it was all below fiber saturation to the core when it went in.

If the core is still above fiber saturation when the lumber goes in the kiln but the surface and ends are below fiber saturation, or if there are small surface and end checks, be sure the conditions in the kiln are at the EMC of the surface. You want to be sure you do not close any checks at the beginning of the drying cycle. If the kiln is new and tight, it is easy to have the EMC too high and close checks and this can cause a lot of damage. Checks should only be closed at the very end of drying

Den Socling

Seems like we are raising more questions than answers. Let's clear things with some definitions. Honeycomb is an internal check that can't be seen without cutting a board. Surface checks can be 'open', 'closed' or 'bottleneck'. Bottleneck checks are closed at the surface but open below and look like honeycomb.

To find out what damaged your wood, cut thin wafers from across the board. If you don't see any cracks, gently bend the wafer to make sure there is no crack. If there is a crack that is tight at both surfaces, you have honeycomb. If you have a crack that continues to one surface, it is a surface check.

If you have honeycomb, the shell was much lower in MC than the core at one point and, when the core was dried faster than stresses could adjust, the fibers tore when the core tried to shrink inside an over-sized shell.

If you have surface checks, the shell had an MC much lower than the core at some point and it cracked when it tried to shrink but the swollen core wouldn't allow it. As you might notice, you can have both honeycomb and surface checks but they didn't happen at the same time.

If you have bottle neck checks, the EMC was too high as Don describes. This makes the surface swell with water and can tear surface checks deeper.

oakiemac

Interesting,  :) I'm learning new stuff all the time.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

jimF

I would say it was surface checked during air-drying.  Surface checks can close up midway into drying and reappear at the end if the conditions at that time are poor.  I tend to agree with Gene W. on the honeycomb part, in that there is no such thing as honeycomb only extended surface checks.  The wafe examination is not fool proof either,  The surface check can run under the surface along the rays and give the appearance of honeycomb.  There is no way to absolutely prove this but I hold to it.
As this episode points out air-drying is not all that gentle of drying method.  One does not have any control of the weather.

Den Socling

If you don't believe in honeycomb, you never ran a vac kiln.  :D And you've never dried a Nothofagus!

beenthere

Quote from: jimF on August 01, 2005, 08:15:11 AM
......  I tend to agree with Gene W. on the honeycomb part, .......

Who would "Gene W." be??????  ::)
Did someone invent a new definition for honeycomb??  I thought honeycomb was describing a particular defect in wood, that Den described quite well a couple posts back.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

willowrunlmbr

oakiemac,

I just gotta jump in and respond.  I run 2 L200's and just found out some useful insight the other day.  I dried 6600bf of 4&5/4 red oak (mainly qsawn) for a customer.  It had been air drying for 6 months, so i was just using a probe meter (j2000) to check the edges.  Got the loads down to 6-7% or so i thought get it to the planing mill and start checking with a pinless and we were getting readings of 14-15% on about a quarter of the lumber.  The point being like Den said (and the delmhorst rep backed up) you have to check the top of the lumber not just the sides, and never the ends.  The sides, especially on the outside of the pack are gonna dry faster, and that 3/4" pin will not penetrate deep enough to give you accurate readings on the edges of the boards.  Use the longer pins, they will give you more accurate readings on the edges.
Super LT40G36, JD544B, NH LX 885, coupla stihls, sore back, and never enough time

oakiemac

Willowrun, what size pins do you use? I guess that I'll start checking surfaces more and not just edges.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

Gunny

oakie:

One thing I always did was to randomly set (where I could get to them) "shorts" (3-4 footers) of the species I was drying throughout the chamber load.  That way, I could always get to them and poke those sweet little holes all over in them to get a real nice read on center-mass MC.  I'll do it still,  now that I'm almost out of retirement again and will soon be firing the L200 once more.  (It only took me a half-dozen loads of trying to snag 100" boards out of the stack in the chamber--with little or no success--to start doing the "shorts" thing.)

BTW:

Where you located?  I have had several customers from SW MI over the years and will be happy to have them drop by your operation too.  I have no intention to go whole-hog this time--just a slow-and-easy lope from now on.

Gary_C

One reason for the checks could be alternate wetting and drying probably during the air drying time. They would not show up until the pieces were fully dried. Allowing oak to regain moisture any time above FSP can cause checks.

Never take life seriously. Nobody gets out alive anyway.

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