March 12, 2013
Slotted construction - It’s a pretty nice thing to do on a CNC router. You just slip one sheet in to another, and if you make the joints tight enough, many times you can have a nice piece of construction with hardly any fasteners or glue…. but there’s always this pesky inside corner problem. You just can’t cut a sharp inside corner with a router bit, but you can do a few clever things to the bottom of the slot to eliminate hand chiseling or filing the inevitable round corners.   The left is your ideal slot. You can make something a lot like this with secondary hand operations, but you want the machine to do the work.  The second drawing shows one way - Reliefs in the bottom of the slot. This is the most easily concealed method, but isn’t quite as strong if the slots will be loaded in a way that forces them in to each other.  The third drawing has its reliefs cut in to the side of the slot. This makes for a large, sturdy base to support sheets that are loaded in to each other, but is also the most conspicuous.  The fourth is a cross of both of these methods, being quite sturdy and not terribly visible, and the corners of the mating slot contact the edge of the relief cut,  but  it takes a bit more effort to draw in CAD. Making these small changes to your design will save a lot of time and stop a lot more of whining from the assembly floor.

Slotted construction - It’s a pretty nice thing to do on a CNC router. You just slip one sheet in to another, and if you make the joints tight enough, many times you can have a nice piece of construction with hardly any fasteners or glue…. but there’s always this pesky inside corner problem. You just can’t cut a sharp inside corner with a router bit, but you can do a few clever things to the bottom of the slot to eliminate hand chiseling or filing the inevitable round corners.  

The left is your ideal slot. You can make something a lot like this with secondary hand operations, but you want the machine to do the work. 

The second drawing shows one way - Reliefs in the bottom of the slot. This is the most easily concealed method, but isn’t quite as strong if the slots will be loaded in a way that forces them in to each other. 

The third drawing has its reliefs cut in to the side of the slot. This makes for a large, sturdy base to support sheets that are loaded in to each other, but is also the most conspicuous. 

The fourth is a cross of both of these methods, being quite sturdy and not terribly visible, and the corners of the mating slot contact the edge of the relief cut,  but  it takes a bit more effort to draw in CAD.

Making these small changes to your design will save a lot of time and stop a lot more of whining from the assembly floor.