Pocket Hole Failure

[Jon Andis]

I have always heard pocket holes are amazing.  I cannot seem to figure it out.  Everytime I try making something, the joints never pull snug and seem very loose.

Anyone have any suggestions or experience this?  I am about 10 minutes shy of selling my K4 on ebay!  Are there any tricks?  I know everyone will swear by the kreg screws, but are there anything out there better?  

[Jay Boutwell]

Jon, I am a professional cabinet maker and have been for going on 30 years now.  I have been using the kreg jig probably longer than anyone on this community group.  I started when the company just started and my first Jig was the K-2 and I have all the jigs made since with the exception of the latest one.  I have not had the problems that most on here seem to have and the  simple reason is that I pitched the directions in the round can and began using my common sense.  When it first came out there were very little directions.  I set the jig up for 3/4 material and used a nickel under the bit tip to insure that I would not over drill the depth of the pocket hole and I do not use the prescribed method of using the clutch setting on the drills and listen to the sound of the driver motor and watch the joint as it seats.   Reasoning is that there is no two pieces of wood that will except a screw the same way and the clutch method is a pre-determined setting that releases when the screw reaches a certain amount of resistance to torque.  That does not matter where or not the screw has pulled the joinery tight or not.  An example to compare with is drilling a pocket hole into pine and then putting a screw in it vs that of red oak.   There is much more resistance to the turning of the screw in red oak than pine and the torque to set the joint tight is much greater but the drill setting does not know that.   It begins the internal measurement of torque as soon as the twisting of the screw begins and it might be only part way into the first piece (pocket hole piece) when the driver decides that the measure is reached and releases its setting and does not turn further unless you increase the setting. 

What your problem sounds like is that you are not tightening the screws tight enough.  If you are using the correct drill depth of the pocket hole and the correct screw length the screw will pull the  joint tight.  Now you will hear and or have read about the screws going through the material exiting the opposite side.  That means one of or a combination of the thickness of the material, the screw length, and then overdriving of the screw.

That is the only thing that it can be.  There are occasions when you will get lumber that is of poor quality and the screw head will drive deeper that the pocket hole seat and or will spin in the receiving piece.  The over driving of the screw often times will cause the screw to exit the receiving piece and the spinning ( stripping out) will result in loose joints . 

Something else that the new generation of Kreg advisors is that glue in not needed however glue is also acts like a lubricant when it is wet and also will fill any minor cracks that appear for the inside of the pocket hole that you might not always see.  Why they advise this is beyond me as it never used to be that way and in some wood, especially plywood it is an extra measure of insurance.   If they argue that the end grain will not glue well it is true unless you take extra time and coat the end grain before you do the glue up and then apply glue again when the joint is assembled.  I have seen common wood glue applied to end grain and attached to plywood or even other long grain and  screwed together and once the glue cures remove the screw and the end grain will pull layers of the plywood and also the long grain off of the opposing piece.  To me that is an indication that glue does infact help hold a joint together. 

I have seen as well as others the test where a joint if prepared using both glue and also without glue and then pressure applied to the joint and the results of the flimsy test is that glue does not help.  What the failure is, is not the glue but the screws resistance to pulling the threads out of the joint.  One of these test was done using a bath room weight scale which really is not test at all.  This test was not a pulling test but a test where pressure is applied 90 degrees to the joint in a shear type test.  Common sense tells me that if the glue bonds to the the opposing piece enough to pull wood fiber off the opposing piece then there must be some benefit of the glue.

I guess you could compare that with the long proven test of time that deck screws and kreg screws using in framing is not a good practice as the shear resistance is not so great.  The new big screw pocket hole jig screws may be different as I have yet been exposed to the new larger diameter screws to make a fair judgment but I do know that a 16 penny common framing nail will still be holding when the screws fail.

As far as swearing to the kreg screw and its usefulness it is a great screw joint as it is fast and strong however it like everything is not always the best solution to a joint.  There are many joints that are far better than the pocket hole joint in some things.   I use the pocket hole joint for such things as holding a cabinet case together,the face frames and other simple joints but I do not use it for making doors and or drawers as many are doing.  To me there are other methods much better than a pocket screw joint not only for looks but also for durability. 

If you want to go back in time like three of four years you will read posts on here about the splitting of joints and the over drilling and loose joints however you will also find out that the reasons are human error and not the jig its self. 

I will say that my opinion is that the recent jigs work off the same simple principal of boring a hole and inserting a screw but the later jigs have complicated and tried to do too much by making them adjustable to do more than necessary.   It is like a common wrench that is a 9/16th size and then grabbing an adjustable crescent wrench to do the same thing.  you loose something in the process and the crescent wrench is known for rounding off bolt and nuts and busting your knuckles.  I had much rather have a tool set up to do one thing and not a toolbox full of things.   Just common sense.  Before you give up on the jig take a look at the past by using the search and type in such phrases as "splitting joint, or pocket hole screws exiting the back of wood and other such phrases.  

[Homer Moyers Jr]

Thank you Jay for some great insight and info when using the Kreg Jig. 

[Jay Boutwell]

I wrote the below article concerning pocket holes and failure and in that article I remarked about some saying glue is not required in a pocket hole joint.  I also made the argument that it did make a stronger joint,  Here is a link to an article that many will find not only educational but also might show what many others think about glue and pocket holes.   

http://www.woodweb.com/knowledge_base/Is_Glue_Necessary_with_Pocket...

[Ken Darga]

Jay,

Very informative read.

Thanks for sharing.

Reminds me of an old saying--- "glue it-screw it"

Jay Boutwell said:

I wrote the below article concerning pocket holes and failure and in that article I remarked about some saying glue is not required in a pocket hole joint.  I also made the argument that it did make a stronger joint,  Here is a link to an article that many will find not only educational but also might show what many others think about glue and pocket holes.   

http://www.woodweb.com/knowledge_base/Is_Glue_Necessary_with_Pocket...

[Glen S]

That does it for me!! Glue & screws on my face frames from now on!! I understand all the arguments form all sides & from my perspective 2 methods of attachment are better than 1.

I've only built a couple frames so far & didn't use glue because there was only a small percentage of structural integrity in a face frame for the cabinet. In hindsight I now understand more than I ever did about pocket holing. The face frame actually has more structural integrity than I had realized.

Thank You Kreg community one & all for all this info!!

[Ken Darga]

My approach, is/has been, 

if it's permanent, I use glue---

if it may be disassembled, for some reason, I only use the screws.

Works for me.

[Glen S]

I understand. Thank You!!

[Mike]

I have been using Kreg jig since k-3 and have moved up to k-5 (btw love the k-5)  I have always used glue. As for not tight enough, I have only had that happen if I over tighten and blow out or don't tighten enough. When put in correctly its a wonderful and strong joint. I agree with Jay, listen to your drill driver and you will learn to hear it. just practice.