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pocket hole joinery and wood movement?

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Forum topic by WoodNSawdust posted 03-11-2015 01:09 PM 2837 views 0 times favorited 12 replies Add to Favorites Watch
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WoodNSawdust

1417 posts in 637 days


03-11-2015 01:09 PM

Topic tags/keywords: workbench wood movement pocket hole question

Is there sufficient play in a pocket hole to allow for seasonal wood movement?
If not, can a pocket hole be elongated by drilling a hole then sliding the jig over a 1/32 inch and re-drilling?

The application:
a 2×4 frame out of “white” wood that will have pocket holes to hold a 2” thick oak top (from an old table) to form my first workbench. Top is 24” x 60” with oak strips that are 2” wide with the grain turned in various directions and then glued together.

Workbench will be located in an unheated / air conditioned shop. Here in Missouri temperatures can range from 100 degrees with 100% humidity in the summer to 0 degrees and no humidity in the winter.

-- "I love it when a plan comes together" John "Hannibal" Smith


12 replies so far

View Bill White's profile

Bill White

4449 posts in 3421 days


#1 posted 03-11-2015 03:07 PM

I’ve used a bunch of pocket hole applications without any untoward results. Just use the correct screw for the application.
Bill

-- bill@magraphics.us

View jmartel's profile

jmartel

6565 posts in 1611 days


#2 posted 03-11-2015 03:13 PM

You can always drill out the hole a bit larger on the side that gets the head of the screw. Go up another size or two of drill bits and it would allow for movement.

-- The quality of one's woodworking is directly related to the amount of flannel worn.

View HornedWoodwork's profile

HornedWoodwork

222 posts in 675 days


#3 posted 03-11-2015 04:32 PM

Yes you can elongate the holes but I would suggest drilling the pocket hole, then drillilng a pilot hole to locate the hole from the other side and cutting away stock from that side instead. The reason I would do this is it will not affect the screw’s ability to bite down and hold, but it will allow for some travel in the wood.

-- Talent, brilliance, and humility are my virtues.

View WoodNSawdust's profile

WoodNSawdust

1417 posts in 637 days


#4 posted 03-11-2015 05:11 PM

Within reason, is there any danger of making the hole too elongated?

Say the actual wood movement is 1/32 of an inch over a year and I make the hole 1/16 elongated.

-- "I love it when a plan comes together" John "Hannibal" Smith

View a1Jim's profile

a1Jim

115202 posts in 3038 days


#5 posted 03-11-2015 05:27 PM

Depending on your use of pocket screws it may be ok but the most common mistake I see online is when folks use pocket screws to connect wide expanse of wood like table tops I defiantly would not recommend the use of pocket screws. There are a number of ways to connect tops that do allow for wood movement.
This thread shows some examples.

http://lumberjocks.com/topics/62485

-- http://artisticwoodstudio.com Custom furniture

View bondogaposis's profile

bondogaposis

4024 posts in 1812 days


#6 posted 03-11-2015 06:08 PM

All joinery methods have to take into account wood movement to be successful. Pocket holes are no different, if you use them where appropriate you will have no problems.

-- Bondo Gaposis

View WoodNSawdust's profile

WoodNSawdust

1417 posts in 637 days


#7 posted 03-11-2015 06:29 PM

@a1Jim: thanks for the link there is some good info there.

Are pocket hole screws strong enough to handle the racking forces involved in fastening a workbench top to the frame when using tools? I would hate to have the screws break off as I was using the workbench.

-- "I love it when a plan comes together" John "Hannibal" Smith

View a1Jim's profile

a1Jim

115202 posts in 3038 days


#8 posted 03-11-2015 06:37 PM

WoodNsawdust
Yes there probably are strong enough not to break, but it will not stop wood movement,so the top will probably crack.
the best solution is to use one of the correct ways to connect the top as outlined in the link I posted.

-- http://artisticwoodstudio.com Custom furniture

View hotbyte's profile

hotbyte

841 posts in 2436 days


#9 posted 03-11-2015 06:45 PM

Two thoughts on use of pocket hole screws…
1) Large/wide panels of plywood/MDF type sheet goods that are stable
2) Smaller width solid boards like face frames where expansion/contraction is minimal.

Stick with other attachment methods like a1Jim’s link for wider solid panels/tops with more movement.

View moke's profile

moke

861 posts in 2237 days


#10 posted 03-13-2015 05:42 PM

+1 with A1Jim….always allow for movement with a table top…...DAMHIKT
Mike

View JAAune's profile

JAAune

1636 posts in 1778 days


#11 posted 03-14-2015 12:20 AM

I don’t trust pocket holes when it comes to wood movement either. I’ll often use them to fasten the center of a table top then pull the sides down with clips inserted into grooves.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View bbasiaga's profile

bbasiaga

754 posts in 1456 days


#12 posted 03-22-2015 09:05 PM

you can also run some cross members between your front and back of your frame, underneath the table. Drill some holes that are oversized for the screws you are going to use, but still small enough that the head will catch. Drill the holes close to the middle so the table top an expand out in both directions if needed. The wiggle room in the screw hole should give it the space. Same idea as the buttons.

Your cross members can be pocket holed in.

I’ve seen this a bunch of smaller tables. Would imagine the idea scales to larger ones.

-Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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