Need some advice on how to back out screws to allow for movement of table top

[Shift]

I'm about to start build a harvest table using 2" (1.5") pine ...

Lots of people suggest backing out the screws a bit when joining the table top to avoid cupping allow for seasonal movement.

My question is just how much do you back them out, and on which joints?

I'm assuming that it's only in the apron to table top joints, and not the edge joints between the actual table top pieces or any of the support structure. Do you back out the screws on the breadboards?

thanks

(corrected the title to avoid confusion for future readers)

[David Dean]

shift I dont see anything wrong with  that table it has pretty top on it and if it was me I would gave it a good sanding and put the ply two it do you now what a table like that in new york goes for.

Shift said:

No ... the breadboards were only attached with screws.

But ... and this is a big, big but ... 

I decided to put one down the middle of the table like in the photo below ... which i now realize means the table is going to look like a pretzel in a few seasons :) Thinking of dismantling the whole top, re-using what i can in another project and redoing the top from scratch.

[Shift]

@David That's not my table  ... really wish it was ....but it's just a pic i pulled off the web for reference after i settled on using narrow boards with an old, salvaged look. I thought that 7 parallel 7ft 2x6's would look a bit like a lumber sale and wanted something to break up the middle and liked the design in the photo. It also meant i was dealing with smaller, more manageable pieces when building the top .

[Larry E Dennis]

I have never "backed out" the screws on any project and I live in the Pacific Northwest where the humidity changes all of the time.  I make sure that the edges of the boards are true and switch the direction of the grain on each board.  Other more seasoned wood workers may have different views, but thats my $.02 worth.

[Pierre Vallee]

Larry is spot on...

[Rick]

Normally ... yes ... but ... if one is trying to allow for movement ... it might have value ... anyone else try it?

Pierre Vallee said:

Larry is spot on...

[Pierre Vallee]

what kind of movement? it's a table top. If you want moverment, leave a small gap.

[Rick]

Movement in the breadboard ends.

He's new to woodworking, and built a table top without sliding tenons.

[Jason Watkins]

Found this in the K3 manual FAQ:

"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. "

[Pierre Vallee]

Jason, I would recommend that 'you be brave' and do it.

[Rick]

And of course, don't use any glue!

[Pierre Vallee]

I wouldn't do the 'back off 1/4 of a turn' but do not overdrive the screw in against the shoulder either. Wood does move, expend and contract with temp and moisture. That's the way the pickle squirts.

[Ken Darga]

Jason,

Don't be afraid to use ''pocket hole'' joinery.

It's a GREAT system.

  I had reservations,  when initially being introduced to it---

once I started, I haven't looked back.

Practice on sample piece of various wood materials and thicknesses.

Make test pieces from scrap or drop-offs.

Make some simple butt joints, such as "T" joints and ''L'' joints,

Use a drill-driver, with the torque setting at its lowest, 

then gradually increase the torque, until you get a tight joint---where the surface at ''butted''---

NO visible gap.

  Affix a ''square'' bit into a screw-driver, or equiv tool, and turn the screw tighter, ''by hand'',

'til you get the feel---you want it SNUG---DO NOT over-tighten---or it'll strip.

Once it's stripped, yo need to ''fill'' the threaded hole---insert ''tooth-pick'' tips until the hole is filled.  Install a few screws, you'll get the hang of it.

As you get confident, you can progress on to projects.

GO-FOR-IT!

You'll like it, I'm sure.

Have fun with your wood working projects.

  NOTE: Pocket hole joinery is not suitable for ''everything'' in wood joinery.

But it sure makes it easier and faster for many joints.

Glue can be added, for a permanent assembly.

  SETTING THE DEPTH COLLAR:

1.  Refer to Kreg's instruction manual and guide on the drilling block.

2.  Position the collar, so the drill point is off the drilling jig ledge, by 1/16'' inch---(the thickness of the nickel)---and tighten the set-screw in the collar.

  Drill tip GAP---some times I use a dime, but that's only when assembling smaller and thinner hardwood pieces and using the smaller screws.

I don't want the drill point tip, poking or breaking thru the piece, in the drilled pocket hole.  

Jason Watkins said:

Found this in the K3 manual FAQ:

"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. "