wood movement question

[Randy C]

I am in final stages of building my Big GReen Egg table top out of a glued up cypress panel. I am including a 18" by 18" piece of granite by cutting a rabbit into the top so that the granite is flush to the top of the table. The table top is 64" wide by 34" deep.

I will be attaching the top to the frame with Z fasteners so that the top can expand and contract. Do I need to worry about the piece of inset granite causing a problem and possibly causing the top to split? 

I have not left any space between the granite and the wood and the fit is reasonably tight. Do I need to add 1/8" to my cut at the front or back of the granite or am I alright as is?

Thanks

   

[Adnick]

Hard to tell from the photo, but I'd give it a 1/16 on each edge in direction of movement....

Andy

[JGrout]

It will need some room for potential movement yes 

If it were me I would skip the z clips add a ledge under the frame and rest the top on that. use a flexible sealant to seal the connection but only to keep water and debris out that way if the seal ever needs replaced you can lift the granite out and clean it after cutting the seal

Joe

[Steve N]

I don't believe the granite is going anywhere (I Googled to see, as I don't have first hand knowledge, and couldn't find a path to follow, wood totally different story.) The wood may move in toward the granite trapping it, and if too tight possibly it could cause a crack. If you allowed the 1/16 to 1/8" around the granite you would be good. If worried about trapping food in the crack, you could caulk it, and it will compress just as it does around windows, and doors.

[Randy C]

No not worried about food getting into the crack. Just want to insure that I don't crack the top because of expansion/contraction.

[Roly]

Is this a 18" square cut into the center of the 34" width ?    I am also assuming the the top  is made up from boards butted up tight to each other with no room for expansion so you  have be be concerned about expansion and contraction across the 18" width, if this is the case along with the fact it is outside, I would think you will need a lot more room in the opening than a 1/8" especially if you have seasons in the area you live.  Roly

[Randy C]

Yes, it is 18" in the center of a panel that is 34" wide and the boards are glued together. But across the grain, there is only 8" on either side of the granite. It will be outside under a covered porch and will have a cover over the table as well.  I would think that 1/16 to 1/8" would be plenty of space for expansion.

Any others have opinions about this?

[jteneyck]

Granite has a coef. of thermal expansion of 4.4 x 10-6 in/in-°F, so your 18" wide piece of granite is going to expand 0.008" total with a temperature change of 100°.  I'd say that's nothing to worry about.  An 8" wide piece of pine might expand/contract 3/32" seasonally. It'll do that around it's center line but on both sides of the frame; so if you make the frame 3/32" larger than the granite all should be well.  

John

[Roly]

The granite is not the problem, the 18" of width across the wood grain is where the expansion and contraction is going to occur.  If you place 18" of solid stone in the opening and the wood shrinks to somewhat less than 18" what will happen ?     Splits along the grain coming out from the corners of the cutout.     I don't know how much room to leave on the width using cypress but it will be more than 1/8" for sure.   Roly

[JGrout]

18" and 1/8" total clearance will just be fine. 

It does not have to be more.