Calculate wood movement
#7
  
I'm building a large kitchen table and the top will be hickory. This is my first experience with hickory. The table will be around 49" wide. The wood moisture content is around 5-6%. I'm having trouble completely understanding the "calculations" to estimate how much movement their could be over time. I was thinking of using Z clips to secure the top, but wasn't sure if I can get the groove on the long sides deep enough to allow for whatever movement there could be. As best I could tell from looking at a few sites, there could be a good amount of movement.
Thanks,
Paul
"Some glue, some brads while the glue dries, and that's not going anywhere!"
Norm
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#8
  Re: Calculate wood movement by plharrison (I'm building a large...)
There are several wood movement calculators on  line. Here's one I've used, but you might want to run it on a few different models and compare the ereults.
I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.
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#9
  Re: Calculate wood movement by plharrison (I'm building a large...)
(02-16-2021, 01:23 PM)plharrison Wrote: I'm building a large kitchen table and the top will be hickory. This is my first experience with hickory. The table will be around 49" wide. The wood moisture content is around 5-6%. I'm having trouble completely understanding the "calculations" to estimate how much movement their could be over time. I was thinking of using Z clips to secure the top, but wasn't sure if I can get the groove on the long sides deep enough to allow for whatever movement there could be. As best I could tell from looking at a few sites, there could be a good amount of movement.
Thanks,
Paul

A problem with at least three variables.  
First, orientation of the annual rings which you have to estimate as radial/tangential for "scientific" information.  
Second, limits of relative humidity in the eventual environment, with your current as a start point.  This translates into moisture content.
Third, the finish applied versus the time available to adsorb/desorb through it through the seasons.  

SWAG - allow an eighth per foot, or so, no need to go above 1/4 per foot.  Best answer to the problem.

Remember to put as many coats under as upon the top when finishing.
Better to follow the leader than the pack. Less to step in.
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#10
  Re: Calculate wood movement by plharrison (I'm building a large...)
The Shrinkulator says it will expand 0.65" for QS stock and 1" for plain saw shagbark hickory if the moisture content gets up to 10%.  Wow, that's a lot.  For pecan hickory the values are 0.45 and 0.84, respectively, still a lot.  Of course, those values are for the whole top and you only have to deal with half that amount from center to edge.  Still, table top clips aren't going to be able to handle 1/2" of movement.  I think I'd consider using some stretchers between the aprons with slots in them.    

FWIW, 49" is a massively wide table.  

John
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#11
  Re: Calculate wood movement by plharrison (I'm building a large...)
John,
Lol, yep it is big, and heavy! My wife wants to potentially seat two people at an end in a pinch, plus three on the side (it is 7' long)! And I think you are right about stretchers in the middle. I didn't feel like Z clips would work on the sides.

And MichaelMouse, your calculations are about what John said.
Thanks!
"Some glue, some brads while the glue dries, and that's not going anywhere!"
Norm
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#12
  Re: Calculate wood movement by plharrison (I'm building a large...)
figure eights depending how they are placed might allow a little more movement when installed correctly than the z clips
and what was already stated orientation , finish details, and humidity
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