Strength determined by screw direction?

[Jack Haskins, Jr.]

My wife wanted small set of shelves built.  Nothing decorative, just functional.  She said getting 1/6 boards and screwing them together would be fine. No sanding. No staining.  Just cutting ans screwing them together.  I put it together with the two sides sitting on the table and the top shelf was on top of the two sides. There are two other shelves inside the two sides.  Since these were not to be used for anything heavy all I did was drill the holes in the location that would hide the holes from sight as the shelf sat where she said she wanted it.  The top shelf is held on with holes drilled up through the side boards. The two middle shelves I put the holes on the bottom of each shelf.  The top shelf is strong as it sits on top of the sides.  The middle shelves are held in place but screws under each with the screw tip at a 90 degree angle with the sides minus whatever angle the Kreg jig drills the holes.  That is what I have right now and I hope it's understandable. 

Now she wants another board on the bottom so if she wants to move the shelf whatever is now sitting on the table (under the 1st shelf) will be on a board attached and part of the shelf.  I can attach the new board under the two sides with the holes drilled into the sides.  Or I can cut the new board to fit between the two sides and put the screw holes on the bottom of the new shelf.  For the new bottom shelf my question is would it hold more weight with it attached UNDER the side boards or INSIDE the side boards.  The boards are only 3/4" thick so there is only so much screw that can be in the board without the Kreg holes.  Actually, this is a question more for curiosity as anything else.  If strength were a big factor in shelves I wouldn't count on just screws when using 1x6 boards.  So just using screws would the bottom board hold more weight with the screw holes in the shelf and inside the two sides or under the two sides with the holes drilled in the sides and the tips of the screws into the bottom board?

Any help is appreciated.

Jack

[KregCS]

Jack, 

In this application, there would not be a huge difference in the strength of your joint between the two ways. However, if you had to choose, I would recommend drilling your pocket hole in the side and going down into the bottom board. Then you have the additional strength of the rest of the bottom board dispersing the weight, instead of just from the screw to the end of the board. If you have any other questions, please let us know and we would be more than happy to assist you.  

[Jack Haskins, Jr.]

Thank you.

KregCS said:

Jack, 

In this application, there would not be a huge difference in the strength of your joint between the two ways. However, if you had to choose, I would recommend drilling your pocket hole in the side and going down into the bottom board. Then you have the additional strength of the rest of the bottom board dispersing the weight, instead of just from the screw to the end of the board. If you have any other questions, please let us know and we would be more than happy to assist you.  

[Carlos]

just my opinion, but I would cut the bottom board to fit between the two sides, I think having the screws going into the side would be a stronger joint, maybe add some glue as well. not to mention that you are also trying to hide the screw holes and won't be able to do so if you put them on the sides.

one more note: how close are the shelves to each other? if you put the holes on the insides of the sides will you be able to get a drill in there to attach the shelf?