Accident Waiting to Happen

The Yew heartwood character bow was brought back today with an almost imperceptible crack showing on the back emanating from an innocuous looking pin knot. (In the first pic I've chiselled out a tiny bit to show the crack better)
I set to excavating a narrow channel following the line of the grain so I can let in a patch. As I chiselled down I could feel the wood round the pin knot wasn't hard clean and solid like the rest of the wood. I've gone down fairly deep over a reasonable length, but how to clean it up to an even curve so I can make a well fitting piece to let in? Ah! I remembered I have an old circular saw blade, I sharpened the teeth over section a couple of inches long (marked with masking tape) and used that, by hand, to clean up the channel to a nice even curve. I'll be able to use the curve of the blade as a template to shape the inlay.
I've done enough for now as it's fiddly work, slow and steady wins the day. Anyway, I'll need to fill the pin knot hole first as I've cleaned that out with a fine drill simply twiddled between my fingers.
In the pics you'll see the edge of the other patch on the limb, maybe I left that area a little stiff and it moved the stress onto the pin knot and caused it to crack, who knows? The good thing is that it was spotted in time and it's interesting that it didn't simply explode, a testament to the toughness of Yew?