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Wide lap joint

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Forum topic by Carloz posted 01-04-2017 06:11 AM 272 views 0 times favorited 2 replies Add to Favorites Watch
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Carloz

304 posts in 131 days


01-04-2017 06:11 AM

I do not know what i was thinking. I made a panel frame from 4.5” hard maple boards and cut lap joints. Now when it came to glueing them it struck me that there is no room for expansion. Now how can i fix it?
1. I can apply glue only at some area of the joint leaving about 2” strips at the end free of glue. A paper mask will help to prevent glue leaking in that area.
2. I can cut a through slot on each half and use dowels in each quarter instead of glue to relieve pressure somehow. Something similar to double tenon.
3. Thash the wood and make new one. Too costly though.
The lap joins are not visible but the rest of the frame immediately next to the joint is.
This is decorative + bearing frame. Must be strong.
Any other ideas ?


2 replies so far

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JBrow

960 posts in 459 days


#1 posted 01-04-2017 12:21 PM

Carloz,

Whenever I glue a relatively wide board cross grain to another board, I use your method 1, but cast care to the wind run glue for about 3”. In this case glue applied 2” to 3” from the shoulder of the lap joint would allow for the unglued section to expand or contract freely.

I played around with the Wood Shrinkage calculator for Flat Sawn Sugar Maple whose moisture content would range from 12% to 8% and it suggests a glued 3” wide stick would expand/contract 1/32”. The full 4-1/2” Flatsawn Sugar Maple could expand/contract as much as 1/16”.

If all sides and the end grain are well sealed when finished, moisture swings in the lumber could be reduced and thus reduce any stress of the glued portion of the joint.

http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkage

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Carloz

304 posts in 131 days


#2 posted 01-04-2017 04:07 PM

Thanks jbrow,
Interesting what shrinkage is safe in a glued joint. I have to idea if 1/16” is acceptable or not.

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