Machinist Skilled Spray-Welding Is Crazy
For most garage dwellers, there are only a handful of known welding techniques. Arc, mig, flux core, and tig. Nobody can blame you for not knowing more, neither did I until I started binging The Science Channel on YouTube. You get bonus points if you remembered spot, plug, ultrasonic, and brazing... For a long time, friction welding was just about the coolest thing to watch, but spray-welding might be the new King of Welding Cool...
Now before some first year welding school pupil fires off an email about how "all welding is essentially 'spray' welding"... Lets not split hairs. I'll concede that I'm not a welding expert, I just thought this looked pretty epic. It's molten metal and fire, what's cooler than that? While there may a dozen different variations of this type of welding, I'll let you Google it yourself to learn more.
If you're wondering why they would resort to such a seemingly wasteful method of repair, those sparks being powdered metal that's not landing in the patch, there's a good reason for it. This type of welding doesn't warp the source material... In this case, the shaft stays straight because of two reasons. One, this type of repair happens at a much cooler temp than traditional welding. And two, as the lathe spins, the heat is evenly distributed. One side doesn't get the chance to expand beyond the other.
A few phone calls out of curiosity proved that while this process isn't cheap, it's much less expensive than just ordering a new shaft in most cases.