Hi Meridee, this is what I got back from JST:
“ You could do it by just winding your 2 threads together on a bobbin under the same tension or - if you are a spinner, just give them a slight twist to hold them together while you weave. I'm pretty sure Jane doesn't do it the second way - she is not a spinner ;-)”
I put my 3 bobbins in three small bowls, and wound them onto an empty bobbin together, but not twisted. They turned fairly well at the selvedge. When they didn’t, I tried, as Jane suggests, to pull the threads that were a bit looser at the selvedge into the shed, the slack being absorbed in the beat. This also worked pretty well, but the group became less cooperative as I came to the end of the bobbin. Having said that, this creates quite a thick yarn so there’s not that much on the bobbin. I knotted the ends when one bobbin ran out. I haven’t washed it yet. So I don’t know what it will look like. This was a bit fiddly, but for a few placemats with leftovers, it works. I have also started winding bobbin ends tied together onto empty tubes in rough color groups, planning to use them as weft for a fluffy scarf some day.
The top half is only the Frankenstein yarn. The bottom half is one pick each of the Frankenstein thread and black - quite different effects.