I have been looking around for a box joint jig lately but decided to design one where I don’t have to set the blade width and opted for a adjustable advance mechanism to match the finger width to the slot cut by the cutter .
The object was to keep the build simple and made from common materials and components but not fixed to fixed index spacing like lead screw and index plate This is a simple sliding table with a fence that slides on a dovetail way and a clamping setup that is mounted on a sliding carriage that is controlled by two adjustable stops in travel length .
The parts to be machined are inserted and clamped by the bar clamp at the front of the jig and held square by the end stop which is typical for this type of jig .
The carriage is set for the beginning cut and held in position by the clamp located at the top rear of the jig .
To set the fence for the second cut I hold the fence with my left hand and release the clamp with my right hand and slide the clamping carriage to the opposite stop and lock it on the clamping rail and then slide the fence and clamping carriage over to the other stop and cut the second slot.
This same procedure is repeated until the fingers and slots are cut .
I remove the material from the jig but leave the fence locked in place for the next cutting sequence
To cut the opposing end I simply flip the boards end for end and start cutting the board using the setup in reverse direction .
So far the results are better then I expected and I will add a safety shield and a turret at the adjustable stops to accommodate different sizes of joint width .
This is a proto type and when complete it will likely include some improvements and changes in safety .
I used a stop block to limit the travel of the sled clamped to the saw to prevent the cutter from exiting through the safety block at the back of the jig but it does not show in the pictures or video .
Let me know what your opinion of this is and also any improvements that can be made I would appreciate it .
Here is a video link that may explain the jig a little better .