Well, that 'mechanic' was an idiot.
If he stuck the stem in the vice, then that means that he hammered on the fork crown, away from the vice ???? He couldn't control the direction of the force and flared the threaded end of the steerer, as the blows moved the fork left and right against the contained stem.
Your only solution may be a large type of nut with a tapered internal thread. As you tighten it on the flared thread, you hope to compress the steerer thread into the tapered nut. Its a longshot. Personally never done it. Dont know where you'll get one. Probably easier to get a new fork.
Is it a precious fork?
Well, that 'mechanic' was an idiot.
If he stuck the stem in the vice, then that means that he hammered on the fork crown, away from the vice ???? He couldn't control the direction of the force and flared the threaded end of the steerer, as the blows moved the fork left and right against the contained stem.
Your only solution may be a large type of nut with a tapered internal thread. As you tighten it on the flared thread, you hope to compress the steerer thread into the tapered nut. Its a longshot. Personally never done it. Dont know where you'll get one. Probably easier to get a new fork.
Is it a precious fork?