Actually I started a long time ago by welding nuts to broken bolts and I've given up on that method unless it's really big and you need the impact to work on it.
Much better luck welding a blob on the broken bolt and using vice grips to turn it out. In my experience welded nuts shear off easier than the blob (of weld) held with vice grips.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-