If you see, I know it is a dark photo. Enlarge it and you may see center of the photo a rectangle area. The bobbin shaft runs into that, and turning the knob raises it lowers that area. You can see the double drive band running over the whorl and bobbin slot.
Just trying to explain this makes me realize I need to do a good photo shoot of the mechanics of the Haldane, they are unique compared to any of my other wheels. So now I have something else on my to do list, but not today. It is dark and gloomy and literally pouring buckets of rain outside right now.
I wanted to make the drive band a tad bit smaller. This would mean less drive band total, which would mean I wouldn't have to tighten the tension as much. It is still a very sturdy drive band in good shape, so I really did not want to cut it off, or find a new one. So instead, I got a thick sewing thread, and needle, and worked on the drive band at the original join. The basic idea was to secure my thread in the join, go up and through the band, just a bit above the join and pull down, pulling in the micro bit of drive band. I covered that with a few blanket stitches with the thread then repeated it several more time, pulling in a little bit more each time. I finished by running the thread all the way down through the join.
The tan thread is the new area. It looks bulky in the photo but travels over the whorl grooves just fine, so it is not as bulky as it looks.
It may not hold. Right now I gained half of my tensioning area, which is more than enough. I spun some on it and could actually do a semi long draw, there was enough pull in. That has been missing from this wheel for quite awhile.