From the photo you embedded it looks like you made a beautiful thumb ring but you designed it to function incorrectly. If you are positioning the string between the black ridge and the lighter tab on the ring you will be putting all the draw pressure on the last thumb bone. So the pressure is mostly applied to your thumb print area. That would be extremely painful even with a moderately heavy draw weight. The thumb ring is designed with an oval opening so that it can be slipped over the oval shaped end of the first thumb bone (the one attached to your hand). But when twisted 90 degrees into its functional position it cannot be pulled off without crushing the flange of the bone. That would take well over a hundred pounds of pull even for dainty bones. Nearly all the pressure from drawing the bowstring should be on the 2 red areas which are shown in the photoshopped x-ray I attached. If you pinch those two areas with your other hand and pull as hard as you can you will feel no discomfort. That's more or less the way a correctly fitted thumb ring should feel. This works best when the string is pulled by the upper lip of the ring and slightly above the joint. I pull a 70lb at 28" Hwarang well past 85lbs with no thumb discomfort. Bending your thumb and holding it with your index finger is really only to lock to draw. If your thumb ring can come off at all in its shooting position none of this works. Hope this helps.
Okay, I think I understand. I'm gathering that I should put pressure away from the joint and more toward the second bone toward the hand. This would explain why my comfortable rings (though they don't fit too well and fly off) are different than the other rings. I tried what Thomas said, and it helps SIGNIFICANTLY, so I may try to fashion a new ring with this in mind.
