My shop-made groove plane (described in this post) saves me from having to make 1/4 inch grooves with a saw and chisel. I was using it freehand following pencil lines, but I decided a fence would be a useful addition.
The fence is simply a block of oak screwed onto the side of the plane. The plane’s blade is not centered in the plane, but 1/2″ from one side and 1/4″ from the other. This allows for different fence distances by simply choosing which side of the plane to mount the fence. Further tweaking of the distance could be made with shims between the fence and the plane to increase the distance, or by making a second fence shaped to decrease the distance.
The plane could still benefit from the addition of a depth stop, but it works well and I am excited about the speed at which I can now make grooves.
Check out these higher-end groove planes Bob Easton made.