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Forum topic by frenchface posted 07-25-2017 09:40 PM 548 views 0 times favorited 11 replies Add to Favorites Watch
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frenchface

7 posts in 350 days


07-25-2017 09:40 PM

I had a some red oak that I dried down to 7-9% MC. I then made a serving tray. The tray has been sitting in my garage for a month and the ends shrunk about 0.25”. Putting my meter on it the tray is sitting around 12% MC from sitting in my garage. I would have expected it to have grown in length and not shrunk. What could I be doing wrong? After you all dry lumber where do you store it so that it maintains <10% moisture?


11 replies so far

View jerryminer's profile

jerryminer

798 posts in 1275 days


#1 posted 07-26-2017 01:40 AM

Can you post a pic? Unlikely that the wood shrunk in length, but maybe something expanded as it went from 7-9% to 12% ?

-- Jerry, making sawdust professionally since 1976

View Ocelot's profile

Ocelot

1856 posts in 2472 days


#2 posted 07-26-2017 02:39 AM

How much did you pay for your moisture meter? How repeatable are the readings? What part of the item are you testing?


I had a some red oak that I dried down to 7-9% MC. I then made a serving tray. The tray has been sitting in my garage for a month and the ends shrunk about 0.25”. Putting my meter on it the tray is sitting around 12% MC from sitting in my garage. I would have expected it to have grown in length and not shrunk. What could I be doing wrong?

- frenchface


View Loren's profile (online now)

Loren

9606 posts in 3481 days


#3 posted 07-26-2017 02:49 AM

The scenario the OP describes is exactly
what would be expected if the item had
breadboard ends. The ends would appear
to shrink as the center expands.

Wood does move a tiny amount along
its length, mostly ignorable in furniture
making but a factor in molding installation.

View Madmark2's profile

Madmark2

371 posts in 422 days


#4 posted 07-26-2017 03:26 AM

“Wood Handbook : wood as an Engineering Material ” free from the USDA has every shrink / grow stat you could want – plus much more!

M

View WDHLT15's profile

WDHLT15

1695 posts in 2310 days


#5 posted 07-26-2017 11:46 AM

Juvenile wood (about the first ten years of growth rings beginning at the core) will shrink a little bit longitudinally.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln. hamsleyhardwood.com

View Ocelot's profile

Ocelot

1856 posts in 2472 days


#6 posted 07-26-2017 01:44 PM

+1

Yes of course. If I had read carefully, of it OP had posted a pic, I wood have realized that!


The scenario the OP describes is exactly
what would be expected if the item had
breadboard ends. The ends would appear
to shrink as the center expands.

Wood does move a tiny amount along
its length, mostly ignorable in furniture
making but a factor in molding installation.

- Loren


View frenchface's profile

frenchface

7 posts in 350 days


#7 posted 07-26-2017 08:15 PM

Here is the pictures

View Madmark2's profile

Madmark2

371 posts in 422 days


#8 posted 07-26-2017 09:23 PM

Oak can move 5% in width, 1/20th of that in length. As a general rule, the “Wood Handbook : wood as an Engineering Material. Really is a must read for these type of q’s.

M

View Tony_S's profile

Tony_S

765 posts in 2916 days


#9 posted 07-26-2017 10:14 PM



The scenario the OP describes is exactly
what would be expected if the item had
breadboard ends. The ends would appear
to shrink as the center expands.

Wood does move a tiny amount along
its length, mostly ignorable in furniture
making but a factor in molding installation.

- Loren

Exactly. The ends didn’t, and wouldn’t shrink to that degree. The tray it’s self expanded in width.
7% to 12% is a pretty significant jump for pre and post construction.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View jerryminer's profile

jerryminer

798 posts in 1275 days


#10 posted 07-28-2017 03:17 AM

Yes—that looks like a classic case of failing to allow for wood movement in the design/construction.

OP: the solid oak bottom swelled in response to the increase in humidity. Call this a lesson in design.

Next time:

A. Make the bottom a “floating panel” that can expand/contract within a frame, or

B. Make the bottom out of a material that doesn’t move so much, like plywood or veneer-on-mdf

-- Jerry, making sawdust professionally since 1976

View JBrow's profile

JBrow

1271 posts in 754 days


#11 posted 07-28-2017 12:18 PM

frenchface,

I agree that it appears that the bottom expanded in width and forced the corner joint apart. Following jerryminer’s advice should reduce the stress on the corner joints.

But the corner joints of the vertical sides caught my eye. These corner joints appear to be butt joints. If the corner butt joints rely on PVA glue only, the joints are inherently weak. The end-grain, making up ½ of the joint, does not seem to take to PVA glue very well.

The corner joints of the sides could be strengthened by reinforcing the joints with screws or dowels. A rabbeted joint, even though an end-grain to long-grain joint would also be stronger with its increased glue surface. The strongest joints of which I am aware for a corner are a splined joint, a locking rabbet joint, a box joint, and best of all, a dovetailed joint. These joints all have at least some long-grain to long-grain glue surfaces. The dovetail joint also imparts some mechanical strength to the joint.

However, even a dovetail joint would not be sufficient to avoid problems caused by a captured and expanding (or contracting) bottom panel. Therefore, even with stronger corner joints, floating the bottom of the serving tray in grooves with room for movement would still be a good idea.

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