Worried about tabletop wood movement...

[Jason Watkins]

Howdy folks,

Just wondering about cross-grain seasonal wood movement in a table i'm building. The top is 4 SYP 57" 2x12 planks with 2x8 breadboard ends. And by breadboard ends I just mean the 2x8's will be pocket hole screwed to the 2x12's. Unless I find a better way.

I've attached the tabletop planks to each other with the proper kreg screws and glue, and also jointed the mating edges.

However, I've not attached the bread boards yet. 

Just wondering if I should take the screws out and let just the glue hold the top together?

I just want to minimize the chances of it splitting in the future. I'm being so particular about this one because it is for a paying customer, the first of many I hope. 

How do we account for seasonal wood movement when using pocket holes, so that our pieces can be handed down to later generations without becoming split or warped?

I'd love to hear thoughts from Kreg on this.

Happy Friday!

-Jason

[Jay Boutwell]

Hi Jason, building a large table is a nice project that presents you with several questions and also challenges.  Since you have built the table top already, using glue and screws that means that everything will hopefully move together.  You may experience some cupping of the 2 x 12  material depending upon the moisture content at the time of the build.  If you have alternated the growth rings this will help control some of the movement from cupping.  When it comes to the bread board ends this can be a problem since if you attach each 2 x 12 to the breadboard end using glue and screws what you have done is remove any  hope of the 2 x 12's moving  as the moisture content causes the grains to swell and contract.

If I was building a project like this I would use splines and grooves in the interior of the table top and then use a long  mortise tongue on the ends.  To attach the breadboard I would use a firm  fitting pocket to except the tongues. To attach the breadboard end I would then use pegs or dowels and fit them so that they would be large enough to allow the 2 x 12 material to move.  (ob-long cut the holes across the grain to allow for wood movement) yet have the peg or dowel tight in the breadboard ends.  The firm fit on the tongue is meaning not to the point that you will have to drive the breadboard on with a lot of force but still tight enough that it is a firm fit. Secure the peg and or dowel with glue.    Depending on the width of the table I may or may not peg each 2x12.  At the least I would place a peg about mid-width of the table and on each end.

Each place you peg the breadboard try to place the peg near the center of the 2X12. This will allow for the wood movement.   Here again there is several things to consider about moisture and woodmovement.  Things like the type and grade of the lumber and how well it is dried.  Stresses applied on it and how much exposure it will be subjected to, and how it is finished.  Good luck with your work as it sounds like you have an excellent attitude when it comes to building something correct.  Doing it right is something you will never regret.

[justin waldron]

Jay is absolutely right, a rule of thumb is for every 12", there could be expansion of up to 1/8 of an inch.  It's a good idea for the bread-board end to leave room inside of the dado to allow for expansion of the top.  Another good idea is when you glue the top itself together, rotate the growth rings on the boards, Meaning the first board, growth rings up, the second board they go down etc.  This will help with stabilizing the top, the only other way to get away with a lot of expansion and contraction is to use quartersawn lumber, wood expands across the grain, since the grain is vertical in quartersawn, the contraction/expansion is minimal.  Hope this helps.

[Terry Scafidi]

   

    Hello to Jason, Jay, and all the others here:

    I am a real beginner in this woodworking and I have a couple of questions about this table construction and the terms that are used. First of all, what is a breadboard end? I have a kind of guess about this because the term is a little self-explanatory. I think I understand what a "mortise tongue" is, but I really can't picture what the use of pegs or dowels will do with the "mortise tongue" on the end of the 2x12's. Jay suggests a "firm fitting pocket to accept the tongues". Wouldn't the firm fit prevent the 2x12's from movement because of weather, or other conditions? Would this then possibly cause the breadboard to split? I guess I just don't understand this very well!! 

    My thanks goes out to all that have replied to Jasons' questions and especially to Jason for submitting his concerns to our forum.

    Here's to good cuts and clear lumber!!!!!

    

[Jay Boutwell]

Terry, maybe this will explain what a bread board is.  It is simply another board running across the ends of other boards with a dato or pocket cut into it to fit over the end grains.  Refer to drawing.

There is a mortise type tongue cut to fit into the dato or pocket.  There is no glue used to attach the breadboard and is held by the friction of the mortise tongue and mechanical fasterners like a peg or dowel.  The breadboard and the mortise tongues has a hole bored throught it that is the same size as the dowel.  The breadboard is removed and the hole in the mortise tongue is modified by cutting the holes oblong to allow movement across the grain but not longways.  The breadboard is slipped over the tennons and then pegged or pined with a dowel through these holes. The purpose of the peg or the dowel is to secure the breadboard to the table top.

The pocket or dato cut in the breadboard is cut with a firm fit to prevent wobbel yet will allow the movement of the mortise tongue within the dato or pocket.  A firm fit does not mean tight requiring it to be forced over the mortise tongues.  The reason it works is the the table top is moving across the grains of the wood from moisture and is moving within a pocket or dato.  Since there is very little movement in the long grain it keeps the table top flat .  I hope this answers your questions.

[Ken Darga]

Check out the ''beadlock joinery".

It has merit.

Can be used in lieu of mortise and tenon joinery.

Glue the loose pieces into the 2x12 stock,

and snug-fit into the breadboard---

secure with dowels into the breadboard, 

as illustrated in Jays sketches.

Beadlock joinery is easier for some to accomplish, who don't have the tools to make accurate cuts, as needed for mortise/tenon joinery.

For 2x stock, use the 1/2'' size beadlock.

  ''Plan your work, then work your plan''.

[Ken Darga]

ps---

Beadlock Tenon Joinery

http://www.rockler.com/product.cfm?page=18092&site=ROCKLER&...

http://www.rockler.com/product.cfm?page=18496&site=ROCKLER

[Ken Darga]

Jay,

Great info.

Thanks for posting the sketches.

You're always helpful.

[Gary roofner]

I did a reveiw about 1 year ago on beadlock pro very easy to use and a very strong joint . The only problem is price of tenning material.

[Jason Watkins]

Hey everyone, thanks for the advice! I wanted to share what I found in the FAQ section of a K3 manual:

"I am afraid to use pocket holes because I am worried about wood expanding and contracting with changes in the seasons. What do you recommend?

There are a couple of easy ways to compensate for this type of wood movement. Let’s assume an example of attaching a rail or apron to a solid tabletop.

First, set your depth collar on the drill bit so you barely drill through the edge of the rail or apron. This will create a larger pilot hole for the screw shank and
will create the effect of a “floating top”. Secondly, drive the screw into the
top until tightened, then back off 1/4 of a turn. This will allow for plenty of expansion and contraction of the wood."

I've decided to forego the "traditional" breadboard ends in favor of "faux" breadboards that can be pulled out to make room for leaves in the table, sort of like the benchwright table from pottery barn. I'll post pics when I'm done.