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Forum topic by Joel J posted 04-25-2018 04:24 AM 422 views 0 times favorited 4 replies Add to Favorites Watch
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Joel J

49 posts in 2501 days


04-25-2018 04:24 AM

I am making a small chest out of 7/8” maple including the top which is 21” wide by 33” long. I have done the glue up, cut 3/8” floating tenons in all three pieces and am ready to assemble. I had planned on pegging the breadboard ends with (5) 5/16” pins (maple dowels) and was going to allow the glued up piece to expand and contract as much and often as needed. My question is this: “Do I really need to allow for movement in a 21” wide board? Can I just glue the joint tight all the way across or would you just glue the center 4” and allow the rest to float”? As always, thanks for all your thoughts and comments. If it matters, I live at 5280’ and the air here is pretty dry all year round.

-- Joel, Denver, CO


4 replies so far

View Woodknack's profile

Woodknack

12945 posts in 2942 days


#1 posted 04-25-2018 04:35 AM

Yes, you need to allow for movement because it’s a crossgrain situation. You can glue the center, glue one side, or not glue at all; just don’t glue all the way across. And no doubt you know, but wallow out the peg holes on the tenons or tongue to allow for movement.

-- Rick M, http://thewoodknack.blogspot.com/

View jdh122's profile

jdh122

1104 posts in 3380 days


#2 posted 04-25-2018 11:49 AM

I wouldn’t risk it, 21 inches is pretty wide. But my climate sees wide seasonal humidity swings. The table in this document http://conradlumberco.com/pdfs/ch12_Drying_Control_of_Moisture.pdf indicates that you have seasonal wood equilibrium rates that vary from about 9.4 to 11% so you might be OK. You could try the experiment, but for my money the extra work involved in pegging it is so small that it’s not worth the risk. If you’re worried about the look of the dowels, drill from the bottom and don’t come all the way through.

-- Jeremy, in the Acadian forests

View Robert's profile

Robert

3571 posts in 2043 days


#3 posted 04-25-2018 01:43 PM

Better be safe than sorry. Its not that much extra work I would just do it.

-- Everything is a prototype thats why its one of a kind!!

View bondogaposis's profile

bondogaposis

5570 posts in 2913 days


#4 posted 04-25-2018 01:45 PM

“Do I really need to allow for movement in a 21” wide board?

Yes, you do. If you don’t allow for it, expect a cracked top at some point down the road. Wood moves, not a lot in a 21” wide board but powerfully enough to crack it open through it’s length. Ask yourself, if a 1/16” wide crack will bother you? If the answer is yes, then allow for movement in your design. Read the Panel Cracked thread to see what happens when you don’t allow for movement.

-- Bondo Gaposis

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