Wood movement question

[PC]

I just looked a several mitered joints (picture frame type) that I did a four to six months ago and noticed that they have all opened up on the outside.

The stock is variously 1 x 2.5 to 1 x 4 oiled and stained birch. The lengths of the sides are variously 12 to 60 inches. The four corners were cut at 45 degrees using an Incra 1000 miter gauge and appeared to be perfect when done.

The inside corners (the short edge) are all tight. The outside corners (3 to 5.5 inches away) have all opened up by about 1/32 to 1/16" Not too much, but enough to be noticeable. All joints were made with biscuits and Titebond II.

I've had the wood in the house for about 8 years. However, I do see significant humidity changes as I am 75 feet from the high water mark (Atlantic Ocean.)

Any thoughts as to why there seems to be non-uniform movement? And more importantly, how to prevent it?

Phil

[Scott Cramer]

The wood has expanded across its width, opening the joints. If you could measure the width of the frame pieces back when you made them, it would be a bit narrower than it is now.

They WERE perfect when done. That was then. ;)

Overall humidity changes, i.e. summer vs. winter, are the culprit. Wait six months, and they will have closed up again or even opened on the inside.

Wood swells and shrinks most along the yearly growth rings. Consequently, flatsawn wood has much greater movement than quartersawn. Planning for wood movement is one of the most difficult lessons I've had to learn. I'd recommend reading Bruce Hoadley's book "Understanding Wood" for the most complete analysis of the subject.

[Bob S.]

The outside miters are closer to the ocean than the inside ones ?

Move further away from the ocean until the joints reach a point of equilibrium....

;)

[Mike]

PC,

I wonder if this is related to the grain direction of the wood. I.e. the rings on the tree. I was watching Frank Klausz the other day (dovetail joints) and he mentioned being aware of what direction you put the rings when building drawers because the corners can cup away from the inside of the drawer out and then not fit in the drawer slot anymore. Thus you flip the wood around so the expansion would be forced toward the box and against the joints (and I assume not really move much??).

It would be interesting to know how the grain looks on your wood. The outer rings have the most tension (since they "wrap" around the wood a longer distance -- think rubber band pulled tight vs not pulled tight). If the outer rings are facing outside your frame that might be the problem.

(newbie with book/video smarts, but not a lot of experience smarts...good luck ;)

Mike

[snip]

[snip]

[PC]

Not on your life. Living on the ocean is the best thing that you can imagine. It sure beats the *#%* of Dallas!

Phil

Bob S. wrote:

[George]

Mike, I'm not sure what books and videos you have, but wood always crowns toward the heart. This may or may not be because the outer rings have more "tension," but heartwood is definitely more dense, in proportion, with harder latewood.

Note that an unprotected log is not compressed by the greater "tension" of the outer annual rings, rather splits radially.

SNIP

[Gregg Germain]

George wrote: : Mike, I'm not sure what books and videos you have, but wood always crowns : toward the heart. This may or may not be because the outer rings have more : "tension," but heartwood is definitely more dense, in proportion, with : harder latewood.

That has not been my experience. My experience is that the wood cups away from the center of the log. The outer rings try to flatten themselves.

--- Gregg

My woodworking projects:

Replicas of 15th-19th century nautical navigational instruments:

of my 82 year old Herreshoff S-Boat sailboat:

FAQ with photos:

"Improvise, adapt, overcome." [e-mail] Smithsonian Center for Astrophysics Phone: [phone]

[George]

[Gregg Germain]

George wrote: : Cup IS the opposite of crown, isn't it?

Is it? I was not under that impression.

--- Gregg "Improvise, adapt, overcome." [e-mail] Smithsonian Center for Astrophysics Phone: [phone]

[Young Carpenter]

um now that you mention it yeah!

[Young Carpenter]

You said they were oiled and stained but never mentioned any finish over that. Oil only minorly retards the loss of moisture, stain even less. "Understanding wood Finishes" Indicates that a thin sealer coat of a material such as Shellac will help even out moisture loss.

[George]