Best Joint Strength

[Marc]

My name is Marc.  I have been woodworking off and on for some 40 years and have up to now been a dowel and glued joint kinda guy.  Primarily furniture.  Cabinets, benches, bookshelves, stools, workbenches, kitchen cabinets/pantry and doors.  

But I am new to using the Kreg joining system and love it.  My first two projects have turned out great!  I am currently building a 16 x 27 inch frame out of 3/4 x 3 inch red oak for my table saw extension.  So I am curious; will I increase strength at the corners by placing the screws on the outside verses the inside?  Or possibly by placing one each way...from outside in and inside out?  The Kreg corners will be hidden by the table saw rails or the insert top either way, so visual concern is not a factor.  Thanks.   

[Don Foley]

Hey Marc,

When appearance is not an issue, such as on shop stands, jigs and the like I often place the screws on both sides of the joint.  From a basic engineering standpoint it seems having screws entering from two different angles would create a stronger joint.  Of course, I still use wood glue even with the Kreg system (unless its a joint I want to be able to remove later).  Extra strength can't hurt.

Don

[Marc]

Thanks Don.  Appreciate your helpful response.  

Don Foley said:

Hey Marc,

When appearance is not an issue, such as on shop stands, jigs and the like I often place the screws on both sides of the joint.  From a basic engineering standpoint it seems having screws entering from two different angles would create a stronger joint.  Of course, I still use wood glue even with the Kreg system (unless its a joint I want to be able to remove later).  Extra strength can't hurt.

Don

[KregCS]

Marc,

Don is correct in that having a screw from each side would give you the strongest joint. However, this is not always possible with the given clearance in your projects. The next strongest way would be to have your holes be on the outside. This would have your screw driving to the meat of the board so that you have the entire piece supporting it. If you drive the screw from the inside you are putting the strength of the joint on the edge of your material. In most applications, this will still be plenty strong, but it does give you a possible weak spot. Hopefully that clears everything up. If not let us know and we will be more than happy to assist you. 

[Marc]

Perfect.  I appreciate your insight.  I had assumed the same logic, but sometimes things are not always what they appear, particularly for newbies with a new tool system.  Better to ask than sorrow later.    

[Steve C]

Remember also that glued wood carries the strength of the wood itself.  This means that if you add a bit of glue to the joint, regardless of where you put the screw... then you are increasing the strength of the joint by leaps and bounds.  I do this when I want to make sure the joint is extra strong and not likely to be one that I intend to take apart sometime down the road.