Expansion advise

[HAMMER23H]

I am making shelf 9.5" wide of cedar and am wondering if I need to compensate for expansion? The ledger for the shelf will be long grain to long grain but at 90°.
edit: Maybe I didn't get my question worded right. I'm talking about the shelf support bracket that is across the width of the shelf board. I'm thinking of using some Kreg screws and enlarging the holes.

[Sawduster]

Sounds to me like you will have an edge glued to a face the length of the long grain of the shelf. While the width of the shelf might change with expansion and contraction, the area of concern will only be the width of the edge glued, so there shouldn't be any issues with grain movement.

[TDHofstetter]

"the shelf support bracket that is across the width of the shelf board"

Meaning... the shelf runs along the wall, and these brackets run perpendicular to the wall, across the shelf? Kinda' like a strap across a door?

Yep. At 9-1/2", the shelf will move enough to be a problem. You can glue & screw within the first (about) 2" from the wall, but anything further from the wall will need to be with some sort of mechanical fastener that allows for movement.

-- Tim --

Member of the
Robert "Limey" Bolton Memorial
International
Volunteer Mentorship and Assistance
Programme

[HAMMER23H]

Thanks guys: Jerry after reading your response I realized I didn't state my question very well,sorry.
Tim I think I already knew the answer but was hoping I could just glue, am going to use pan head screws and oversize the hole and put a plug over the screw.

[rrich]

Here is the numbers from the USDA manual.

Elm - Cedar will shrink about 1%, radial and 2% tangentially for each 6% of moisture content change.

So a 10" shelf will change about 1/4" per 6% of moisture content change across the width of the board.

Typically a KD board contains 6%-7% moisture content. In the summer your 9" shelf will grow about 1/4" and shrink back to the size that you just made it during the winter.

[HAMMER23H]

Rich if I understand you correctlly a quarter sawn board will expand 1/2 as much as a flat sawn board for the same amount of moisture change. The cedar that I used has been stored in a barn for the last 15 years. First time I ever worked with cedar, it's kind of soft.

[TDHofstetter]

Yep, you understand correctly.

Cedar... is VERY soft. You can easily push your fingernail into it. For ref, pencils are made from Port Orford cedar.

EDIT: Cedar is also a "best choice" for certain purposes because its strength-to-weight ratio is nearly off the charts. Top-quality canoes & guideboats are very often made of cedar for that very fact.

-- Tim --

Member of the
Robert "Limey" Bolton Memorial
International
Volunteer Mentorship and Assistance
Programme

[rrich]

Thanks Timmer.