Get a sharp bradawl or similar, and chase the threads with that at an oblique angle. Other than getting a large diameter tap, there isn't much more you can do. Don't under-estimate the virtue of smacking the fick out of it on a hard surface with a decent hammer to shirt the crap out too.
Get a sharp bradawl or similar, and chase the threads with that at an oblique angle. Other than getting a large diameter tap, there isn't much more you can do. Don't under-estimate the virtue of smacking the fick out of it on a hard surface with a decent hammer to shirt the crap out too.