Sawing against the Wind
Join Date: Dec 2010
Location: God's beautiful hills of Middle Tennessee
Steve gave you some great advice, I'll add just a little bit more to it. YOU are not the first to do a constricted joint of some sort so don't feel bad.....IF we all are truthful sometime in our beginnings did one.....sadly there's still a lot that do them. Just do a search here about tabletop issues/problems, there's a LOT of info AND arguments over what to do or correct. It's usually a cross between starting moisture content of the lumber and the final destination MC.....this is where proper joinery needs to be learned. Jay Whitecloud here has GREAT info as he works for a living dealing with higher MC wood that takes long term movements over years to finalize (It actually NEVER stops changing, it usually gets to a decent balance point that the movement isn't AS NOTICED!)
Also when building a long table. most have shorter breadboards at what most consider the ends for a reason.....it's a shorter wood movement so it's less noticed from summer to winter and back transition. On a law of average once everything gets MC balanced to it's "home" enviroment....a 42" top will move approx (this depending on location and humidity) a 1/4" across grain with some woods moving more and others less, which equals out (if anchored solid in middle) to approx 1/8" each side or way. Length wise there is very little movement in the wood. The direction your "breadboards" run you can expect double as you have a LONG cross grain area of movement.
There's wood charts with movement expectancy of all the woods produced, there's joinery charts, RH vs MC charts, etc., etc. that need to be researched and used/learned.
Sealing/finishing.....BOTH.....BOTH......BOTH sides (top and bottom) have to be sealed. This helps with MC changes and warpage.....a finish ONLY slows the MC changes. Example...IF you only finished one side as the MC made a big change/swing the unfinished/unsealed side would move quicker than the finished/sealed side causing the wood to move more/faster on one side and cup/warp.
Interesting design....post us some pics once corrected and finished!!!!
Have a Blessed and Prosperous day in Jesus's Awesome Love, Tim
........www.TSMFarms.com.......... John 3:16-21 ..........
Reveling God's awesome beauty while creating one of-a-kind flitches and heirlooms.