Replies

1. 
   YesMaam27577 | May 08, 2009 12:09pm | #1

   Actually, I think it will depend if the corbel is flatsawn or quartersawn.

   When thinking of wood expansion, you need to think in terms of the annular rings in the tree. Now think of each ring as a circle.

   Now, understand that (in general) when wood expands with humidity/moisture, each circle gets a bit bigger in diameter -- but the line with which the circle was drawn does not get thicker. (at least not significantly).

   So, flatsawn boards will expand considerably more than quartersawn boards, which are quite stable along the quartersawn face.

   Politics is the antithesis of problem solving.
1. 
   Fabe | May 08, 2009 06:01pm | #4

   A good point. A quartersawn corbel, though not what the designer had in mind, should work. Personally, I think a better solution would be to run the grain of a plain sawn corbel horizontally. That would move the crossgrain construction problem from the tabletop to where the corbel meets the support/ledger plate at the back wall. There, the problem would be replicated because the grain of the support plate is to run vertically, but a construction that would allow for wood movement when securing corbel to plate would be much simpler to come up with. Another big advantage is that the corbel would be glued to the tabletop long grain to long grain, rather than end grain to long grain.

   Actually, the real difficulty I'm facing is is not finding a construction that will work. It is to convince the designer that there is a problem. Though not my boss (we are just two guys working for a common friend), he appears to be very determined not to see the difficulty, and to micro-manage all aspects of construction.

    

1. 
   YesMaam27577 | May 08, 2009 07:44pm | #5

   >>"...the real difficulty I'm facing is is not finding a construction that will work. It is to convince the designer ...."Well, now there you go. "To convince the designer" is a concept that has never really come to fruition. There have been a determined few, who thought that they were able to do this. But as soon as the designer was no longer in the same room...........Seriously -- perhaps your designer would benefit by taking a guided tour of the Shrinkulator website. It's an online movement calculator, with inputs for species of wood, and humidity changes. It would at least show the facts.And the facts are, as you know, and as saschafer has shown, that the designer's plan will cause movement of almost 1/4 inch.

   Politics is the antithesis of problem solving.

2. 
   hammer1 | May 08, 2009 03:49pm | #2

   If you have movement concerns, why don't you just mount with a method that allows for it?

   Beat it to fit / Paint it to match

3. 
   saschafer | May 08, 2009 03:50pm | #3

   Assuming a worst-case humidity swing of from 30% in the winter to 50% in the summer (reasonable for conditioned spaces), that's about a 3-point swing in the wood's moisture content. The wood won't change significantly along the grain, so all we have to worry about is the movement of the corbel. If it's 20" wide, we get a total excursion of:

   • quartersawn: 0.10"
   • flatsawn: 0.22"

   In either case, it's a good bet that something is gonna give. But it really, really depends on how much humidity variation there is over the seasons. Some people keep their houses humidified in the winter and air-conditioned in the summer, to the extent that the humidity variation is much less.

   -Steve

    

    

1. 
   SteveSchoene | May 08, 2009 11:50pm | #6

   I agree with your calculations, though I'd think it likely that the range of RH could be even more more.  Not so much in the ordinary course, but in the exceptional case--for example: the family is on vacation when a power failure leaves the AC off for a couple of weeks.  And, depending on where he lives, a real cold spell can get the humidity below 30% pretty easily.  Whether the homeowner is sensitive enough to the dryness to add humidity isn't something I'd want to bet a call back on.  I'd want to plan for the occasional exceptional case and add a point or two of humidity range, just to be on the safe side. 

   The answer is the same.  Make sure the construction allows for the wood movement.  There ought to be plenty of options so invisible that the designer need not be consulted.   

    

1. 
   Fabe | May 10, 2009 01:44am | #7

   Steve, I agree with all you've said to Mr. Schafer, including your mentioning that solutions are not difficult to come up with and to hide. However, when I raised the problem of gluing across grain with the designer and proposed obvious solutions he just flatly denied the problem. I would never have raised the issue on this forum save that he seemed to have a reasonable amount of  experience and had me wondering if I was missing something. I have been reassured by what you and the others have said, and feel - not good about - but justified in quietly working around the flawed design while keeping my mouth shut . Thanks. Fabe