A rigid heddle needs to be threaded as you warp the loom, right? What if there were one that you could attach to the warp AFTER the warp is wrapped on the loom?*
I came up with an idea for a rigid frame with wire heddles that opens at the top. The eye in the heddle is a coil instead of a closed loop. I can slip the thread into it with a special twist. Then the frame closes for weaving. The prototype is made with cardboard but I plan to make a wooden frame for the next one and am learning to bend the wires much more precisely. To test the prototype I wrapped a continuous warp around a biscuit box. I anchor the box between my knees to weave.
My first two tests were warp faced bands, one of heavy yarn and one of shiny finer thread. The heddles performed better with the heavy yarn, I had lots of trouble with the finer thread getting caught when it tried to slide past the eye, especially on the outside edges of the band.
The current test is heavy yarn in even weave. This test works more easily than the warp faced bands, perhaps because the outside threads don't have to pull in so much. I will go ahead and refine the design for the wooden frame version. I picture it being useful for weaving bands on an inkle loom or wider fabric on a backstrap loom.
*Note: There is an open-topped heddle for the Brinkley loom. It has a heavy rod heddle with slits in which you lay the warp threads. Turning the heddle over changes the shed which is very ingenious. (I've seen this in use at a demonstration at Wool Fest from this company http://plantdyedwool.co.uk/)