Pocket Hole Orientation and Strength

[J]

I am building a coffee table out of 2x2's and wanted to hide the pocket hole so that they arent visible. Below is what I have build so far, I am also going to have 40" rails connecting the 2 square frames. By placing the pocket holes on the top of the vertical axis for the top rail and bottom of the vertical axis for the bottom rail the top rail pocket holes will be covered by the table top and the bottom rail pocket holes will be facing the floor.

My question is what is the strength tradeoff of placing the pocket holes on the top size of the vertical axis? Would it be any stronger if I placed the pocket holes on the bottom size of the vertical axis for the top rail or if I moved all the pocket holes to the inside of the horizontal axis? Does my design provide sufficient strength for a coffee table?

[Tim Grace]

In my opinion, what you have is the way it should be done, with the top and floor sides concealing the pocket holes.  I believe it to be the strongest option.  

Going from the underside of the top rail, you will come closer to the edge of the end grain, and stands a greater likelihood of splitting the uprights.  

The side option would probably be the second best option.

[J]

Tim, thats exactly what I thought when I originally put it together. By concealing the pocket holes I was also directing the screws towards the center of the piece of wood they were screwed into. If I put the pocket hole for the top rail on the bottom side of the vertical axis the screws would be directed toward the edge. Even thinking about it logically for the top rail the screws are going into the wood at an angle similar to what one would use to hang a picture on the wall which would be good for support against downwards pressure.

I got a little worried when I saw this test for the Kreg HD joint and it make appear that my orientation would be weak. What I did is equivalent of the Type 1 joint with Bottom Pressure.

Source: https://www.kregtool.com/webres/Files/KregJigHDForceTestSheet.pdf

Tim Grace said:

In my opinion, what you have is the way it should be done, with the top and floor sides concealing the pocket holes.  I believe it to be the strongest option.  

Going from the underside of the top rail, you will come closer to the edge of the end grain, and stands a greater likelihood of splitting the uprights.  

The side option would probably be the second best option.

[Tim Grace]

The difference is that in the HD example the force is being applied to the top rail in a downward direction.  In your design, the normal forces would actually be applied to the styles (uprights), and not the rails (horizontal pieces), in a downward direction.  In your design, the rails would not be subject to forces shown in the HD example.  The weakest would be a corner to opposite corner force, for example: someone falling into the long edge of the table.

[KregCS]

J, 

The HD stress test is correct and the results would apply to the smaller jig as well as far as which option would be stronger.  However, the HD jig is meant to be used in structural applications so there can be vast amount of weight being applied.  With the standard jig, there is not as much of a difference in strength between each application so either way would be sufficient.   If you have any other questions please let us know.