max width across the grain of a panel before it needs to be truly floated??

[kooshball]

I am making good progress with my bed project and will be doing joinery and glue-up very soon. I have side rails that are basically made of 6" x 3/4" x 80" walnut between two rails that are 1 3/4 x 2 1/4 (I plan to glue these together using a rabbet to make a "side beam". My footboard however is the same setup but with a 7 3/4" x 3/4 x 60" walnut panel. Can I glue this up as one piece or is 7 3/4 inches wide enough to generate significant movement and necessitate that piece to float between the rails and the legs?

Thanks

 

[Trent Mason]

I would think that at 7 3/4" you should be fine, but wait for other people to respond.

The head board and foot board on this bed frame that I made are each about 20" wide and are each made up of two 10" +/- x 3/4" x can't remember the length, that were tongue and grooved, glued together and glued into the posts. I never had any issues with movement.

 

[jlimey]

I start to worry about wood movement with hardwood widths greater than 4". This is conservative, but I would rather be safe than sorry. A walnut board as wide as yours might move almost 1/8" going form 30% to 60% RH. If the wood is not allowed to expand/contract, what would happen? I would make it a 2 tenon joint, the bottom fit tightly, with the top having a little room for movement (and no glue). That being said, given today's climate control, the piece may never see such changes in relative humidity.
It is not uncommon to see wide boards on old case work that have splits. I saw a gorgeous tallboy of walnut a few weeks ago that was nicely done. Fine dovetails, nice bonnet and mouldings - but each side had a crack in the carcase. It was considerably wider than your board, but another reminder of the power of wood movement.

 

[Jeff]

I am making good progress with my bed project and will be doing joinery and glue-up very soon. I have side rails that are basically made of 6" x 3/4" x 80" walnut between two rails that are 1 3/4 x 2 1/4 (I plan to glue these together using a rabbet to make a "side beam". My footboard however is the same setup but with a 7 3/4" x 3/4 x 60" walnut panel. Can I glue this up as one piece or is 7 3/4 inches wide enough to generate significant movement and necessitate that piece to float between the rails and the legs?

Thanks

Two articles that may help you out, both are authored by Christian Becksvoort:

"Understanding Wood Movement" (FWW 2003); a section within addresses bed construction.

"Stop Guessing at Wood Movement (FWW 2006). You can calculate the anticipated expansion and contraction of your footboard based on its current width, current equilibrium moisture content (EMC), and contraction at 6% MC or expansion at 16% MC.

The calculation parameters allow for either quartersawn or flatsawn.

Good luck and let us know how you decide to deal with it. ccasion1

 

[jlimey]

Here is a link to a wood movement calculator that might be useful.

jeff

http://www.woodbin.com/calcs/shrinkulator.htm

 

[kooshball]

Those articles are excellent thanks to all for the replies.