the theme to this thread is: how not to break my next one, medicine, that wasn't a hijack, man that was good advice!
denny thanks VERY specific advice on how to cut the shelf. that's exactly what i wanna hear.
i do deeply love the arrow shelf, when it doesn't lead to these breaks. i think my initial error was following Sam Harper - a MUCH more skilled bowyer than i- who skillfully cut his shelf even past the centerline and still made it work. i think i'll cut me an extremely cautious arrow shelf, or just build up a little piece of wood on the side for this next one.
thanks all for the encouragement.