You can cut one end of all four box sides at the same time, but you will need to devise a way to shift two opposite sides of the box an exact amount equal to a pin width, because two of the boards will need to start with a pin and the mating pieces will need to start with a space for the mating pin on the other board..
Remember the "A" and "B" sides that I referred to? Two have to start with the pin first and the other two have to start with the space for a pin first. I use one of the boards that start with the pin first to shift the boards by the width of the first pin (already cut board inverted to use first pin as spacer when making first cut of boards beginning with the space first). You can then remove this already cut "A" board and continue cutting the rest of that end of the "B" board to complete that end of the board. Grouping the "A" boards together and cutting both at the same time only requires a clamp to keep them aligned with each other. The "B" boards not only require the clamp to keep them together, but use of the "A" boards to space the "B" boards over during the first cut so they begin with a pin space and not with a pin. From then on, as long as the two boards being cut don't shift in relation to each other, you can cut both at the same time and your joint will be good.
I just found that when I cut one board at a time that it's been easier for me to get a perfect joint. If I was doing production mode I might be willing to cut more at the same time, but it would require ways to quickly align and clamp them together as well as a spacing method to use when cutting the "B" boards. This is true whether you are cutting the joints with the I-Nox jig or the Incra jig or any other jig to make box joints and with the Incra LS and the strips to guide you as to where to position the Incra Ls to make each cut. They won't fit together if you cut all four pieces identical. Well, they will, but two of the sides will be shifted by one pin width, requiring you to trim the box sides narrower for the top and bottom edges of all four sides to be in alignment with each other and waste some of the wood, resulting in a smaller box than you intended to make.
This will all become very obvious to you if you cut both ends of all four box sides of your first box the same and then try to dry assemble the box. Then you will fully understand why I label the front and back of the box "A" and the two sides of the box "B" and cut them differently, and why I tend to prefer cutting one end of one side at a time, or both "A" sides at the same time and then both "B" sides at the same time, but never all four together at the same time.
Central North Carolina
Last edited by CharleyL; 07-23-2018 at 10:09 PM.