Here is a ¼” box joint jig that is a bit unconventional. To use:
1. Attach a piece of 2x material to the miter gauge.
2. When you know the width of the material you want to cut a box joint in,
3. Set the material, right side against the dado blade.
4. Set the stop block against the left side of the material
5. Start with a ¼” spacer to index the material to the wood the distance of ¼”
6. Make the cut.
7. Replace the ¼” spacer with a ¾” spacer and make the second cut.
8. Combine the ¾” spacer and the ½” spacer and make the third cut.
9. Continue until all the cuts have been made.
This method is a bit labor intensive, but it eliminates the need to get that first pin exactly right. I wouldn’t use this method if I had a lot of joints to make. For a one off project, it might be fun to use. This can also be used for 3/8” box joints, by changing the sizes of the spacer blocks.