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oak expanding contracting after months

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Forum topic by megabork posted 12-02-2019 06:46 PM 495 views 0 times favorited 15 replies Add to Favorites Watch
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megabork

21 posts in 402 days


12-02-2019 06:46 PM

So i milled some oak off of 8×8 beams then dried them in my makeshift kiln to 9.6% on the moisture meter and then built a large tble only to see after 6 monts the thing start going crazy splitting and separating, huge 1/2 inch cracks within the wood not even on the glue joints .I cant even imagine how much force it takes to split 3/4 inch oak.. any idea how this happens how to avoid in future? I get these beams for really cheap from a friend who works on the docks


15 replies so far

View CaptainKlutz's profile

CaptainKlutz

2041 posts in 2056 days


#1 posted 12-02-2019 07:09 PM

Tough break.

There is lot of science to Drying wood + Tons of online references.
https://en.wikipedia.org/wiki/Wood_drying
https://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf

Questions:

Did you check the MC in center of board, after cutting it?
- With thick lumber, the center can/will be at a different MC than outside.

What was temp and how fast did you dry it?
- If you dry lumber too fast and/or too hot; you case harden the outside, which reduces the ability for moisture to evaporate from center. Later the case hardened outside cracks as the moisture is released.

Cheers!

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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megabork

21 posts in 402 days


#2 posted 12-02-2019 07:47 PM

yeah i think the drying process wasnt right i used a heater and dehumidifier im gonna readdress that next time for sure i was more concerned with warping

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bondogaposis

5570 posts in 2913 days


#3 posted 12-02-2019 07:57 PM

Besides your wood being too green, it very much depends on how you attached the top to the base, did you allow for movement?

-- Bondo Gaposis

View JohnMcClure's profile

JohnMcClure

815 posts in 1202 days


#4 posted 12-02-2019 08:03 PM


Besides your wood being too green, it very much depends on how you attached the top to the base, did you allow for movement?

- bondogaposis


^This.
Much of joinery is not how to connect boards, but how to connect them in a way that allows for movement. Wood expands and contracts in thickness and width, but not (appreciably) in length, with changes in humidity. So if you screwed a batten underneath your tabletop, that could cause what you described. If you used figure-8s or any of the more elaborate methods, with a little wiggle room, then it’s got to be down to uneven moisture content as discussed between inside/outside of the boards.

-- I'd rather be a hammer than a nail

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Aj2

2565 posts in 2360 days


#5 posted 12-02-2019 08:04 PM

I bet they are from the center of the tree or close to the pith.
Now you have a nice rustic farmhouse table

-- Aj

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megabork

21 posts in 402 days


#6 posted 12-02-2019 10:23 PM



Besides your wood being too green, it very much depends on how you attached the top to the base, did you allow for movement?

- bondogaposis


I glued it with dowels how else ?

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megabork

21 posts in 402 days


#7 posted 12-02-2019 10:24 PM


Besides your wood being too green, it very much depends on how you attached the top to the base, did you allow for movement?

- bondogaposis

^This.
Much of joinery is not how to connect boards, but how to connect them in a way that allows for movement. Wood expands and contracts in thickness and width, but not (appreciably) in length, with changes in humidity. So if you screwed a batten underneath your tabletop, that could cause what you described. If you used figure-8s or any of the more elaborate methods, with a little wiggle room, then it s got to be down to uneven moisture content as discussed between inside/outside of the boards.

- JohnMcClure

Besides your wood being too green, it very much depends on how you attached the top to the base, did you allow for movement?

- bondogaposis

^This.
Much of joinery is not how to connect boards, but how to connect them in a way that allows for movement. Wood expands and contracts in thickness and width, but not (appreciably) in length, with changes in humidity. So if you screwed a batten underneath your tabletop, that could cause what you described. If you used figure-8s or any of the more elaborate methods, with a little wiggle room, then it s got to be down to uneven moisture content as discussed between inside/outside of the boards.

- JohnMcClure

i dont use screws

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megabork

21 posts in 402 days


#8 posted 12-02-2019 10:26 PM



I bet they are from the center of the tree or close to the pith.
Now you have a nice rustic farmhouse table

- Aj2

lol I fixed it luckily very dark color looks good but yeah

View DS's profile

DS

3345 posts in 2982 days


#9 posted 12-02-2019 10:32 PM

+1


Besides your wood being too green, it very much depends on how you attached the top to the base, did you allow for movement?

- bondogaposis

I believe he is referring how it is attached to the table base and/or aprons.

A board that size (tabletop) can shrink, or grow, almost 1/2” in width with seasonal changes.
If the outer edges of the table top are rigidly affixed to the base or apron, the shrinking board will split open in the middle somewhere.

Some kind of joinery that allows this inevitable seasonal movement to occur without catastrophe will accomplish a nice table even if the moisture is high, or uneven, etc, etc.

There are many, many, methods that work to attach the table top and still allow for seasonal movement.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View DS's profile

DS

3345 posts in 2982 days


#10 posted 12-02-2019 11:53 PM

Opt 1.
Cut a dado slot in the top of your apron and screw this bracket to the underside of your top.
(An equivalent all wood version works too)

Opt 2.
The aforementioned figure eight. Using a paddle bit, recess this into the top edge of your apron and attach with a screw. The other half of the figure eight forms a tab that can receive a screw into your top from underneath. As the top shrinks and grows, the bracket will swivel in place.

Opt 3.
Slotted screw holes. You can still fasten the apron directly to the top, but on the outer edges, the head end of the screw in your apron is inside a elongated slot instead of a single drilled hole. This allows the top to slide over but remain attached.

Opt 4.
French dovetail table base support underneath a slab top. This is definitely a style choice as the underneath supports are visible along the edges of the top. The top is press fit onto a support that is inside an over-sized dovetail slot. The top can expand and the support is firmly affixed to the base.
DO NOT USE GLUE in this joint!
A screw or dowel in the very center plank will prevent any slide out failure and the edges can still move.

Opt 5. et. al.
Use your imagination, search google, search forums like this one. There are likely dozens more creative ways to solve this issue.

Good Luck

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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megabork

21 posts in 402 days


#11 posted 12-02-2019 11:57 PM



+1

Besides your wood being too green, it very much depends on how you attached the top to the base, did you allow for movement?

- bondogaposis wow I never even occurred to me, I try not to use hardware at all, tenons, dowels etc but what you described is definitely what happened .. I will look into the dove tail you described as im going to begin a large dineing table thanks for all your help guys

I believe he is referring how it is attached to the table base and/or aprons.

A board that size (tabletop) can shrink, or grow, almost 1/2” in width with seasonal changes.
If the outer edges of the table top are rigidly affixed to the base or apron, the shrinking board will split open in the middle somewhere.

Some kind of joinery that allows this inevitable seasonal movement to occur without catastrophe will accomplish a nice table even if the moisture is high, or uneven, etc, etc.

There are many, many, methods that work to attach the table top and still allow for seasonal movement.

- DS


View Axis39's profile

Axis39

109 posts in 159 days


#12 posted 12-03-2019 02:21 AM

When building any big project, like a table, or solid wood cabinetry/bookshelves, etc. I try to let the wood sit in my workshop for as long as possible… A year makes me happy. Kiln dried or not, it needs to rest. A lot of the time, if I can, I will also let it rest in between big changes in size.

Of course, this is a tough way to work, and almost impossible when it comes to commission work. But, it’s always nice when I can work this way.

My wife looked at me sideways when I packed up the maple and walnut boards I’ve had in my workshop for more than fifteen years when we moved across the country. Of course, now I’m in a way different environment and gonna have to let them settle in all over again. Good thing I don’t have anything specific to build for her out of them!

-- John F. SoCal transplant, chewer uppper of good wood

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Lazyman

4181 posts in 1949 days


#13 posted 12-03-2019 03:52 AM

One other thing that could contribute is case hardening caused by drying too rapidly. Red oak is especially susceptible to it. Make sure that you do not have a fan blowing directly on the wood inside your DIY kiln. A fan blowing on the wood will usually contribute to case hardening. In effect, you dry the outside too fast which sets it so that it cannot shrink as the inner core dries. You often see some significant wood movement as you mill and saw the wood which can relieve the stress but even if you do not, there could be considerable stress in the wood that eventually has to be relieved, though cracking warping and twisting. It can be especially dangerous if you saw a case hardened board and it releases as you are sawing.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View megabork's profile

megabork

21 posts in 402 days


#14 posted 12-04-2019 07:16 PM



One other thing that could contribute is case hardening caused by drying too rapidly. Red oak is especially susceptible to it. Make sure that you do not have a fan blowing directly on the wood inside your DIY kiln. A fan blowing on the wood will usually contribute to case hardening. In effect, you dry the outside too fast which sets it so that it cannot shrink as the inner core dries. You often see some significant wood movement as you mill and saw the wood which can relieve the stress but even if you do not, there could be considerable stress in the wood that eventually has to be relieved, though cracking warping and twisting. It can be especially dangerous if you saw a case hardened board and it releases as you are sawing.
definitely happened thanks..i don’t have the luxury of waiting years to buildand yes it was red oak lol

- Lazyman


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avsmusic1

542 posts in 1247 days


#15 posted 12-04-2019 09:07 PM



One other thing that could contribute is case hardening caused by drying too rapidly. Red oak is especially susceptible to it.
- Lazyman

This is where my mind went. Drying oak is a PITA in my experience. I dry oak as slow as I can without getting mold

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