How much room should I leave?

[Dick Holt]

I am building a chimney cupboard for my daughter. The back will be pine beadboard (from the BORG). I was wondering how much room I should allow for expansion between the individual pieces. The beadboard is approx. 3 1/2" wide and a nominal 3/8" thick. The tongue is 3/16". The humidity is my shop is about 40%. I know if I snug up the boards they will expand and possibly split in the summer. How much room should I leave? Thanks for your help.

Dick

[Judson Green]

I've left about a nickel thick when I last did any bead board.

[Todd Burch]

Judson's idea is good. If you can locate two nickels, so you can space the same at the top and bottom, you've just invented a new woodworking gauge that you could package and probably sell for a quarter. ;)

But seriously, I never go tight on T&G panels. Unless, of course, the wood is green wet, and then I couldn't get them tight enough. Your pine should be expected to be at ~19% or lower from the BORG.

[John TenEyck]

If the wood is in equilibrium with your shop, which it will be after a couple of weeks assuming what you bought was KD, then it will be at about 7.5% MC at your shop's 40% RH. Next Summer the humidity might go up to 70% in MA, unless you have central AC. Assuming you don't, then 3.5" wide Eastern White Pine boards will expand

3.5 x 0.061 (0.13 - 0.075/0.28) = 0.042" or just about 1 mm.

A dime is 1.35 mm thick, a penny 1.55 mm and a nickel 1.95 mm. I'd use a dime.

Bruce Hoadley's book "Understanding Wood" should be on everyone's shelf.

John

[Judson Green]

Judson's idea is good. If you can locate two nickels, so you can space the same at the top and bottom, you've just invented a new woodworking gauge that you could package and probably sell for a quarter. ;)


Thanks Todd


I'd use a dime.

John


But 2 dimes + Packaging + marketing =:(

[Judson Green]

But honesty if ya look at the profile the beading will tell you how much... what looks right.

[Dick Holt]

Great help guys! Thanks for the info, this is just what I needed.

Dick

[John TenEyck]

But honesty if ya look at the profile the beading will tell you how much... what looks right.

What might look right in the Summer is likely to look awful in the Winter if you follow that approach.

John