Welding.

[timster2]

With everything controlled by a computer circuit best to disconnect. Attach the ground as close to the part to be welded as possible. Take care not to have the current travel through bearings or ground straps. Many will say hey I don't disconnect and everything is OK, however, few will admit that they fried something. Because the failure was not immediate and happened some time after the welding job sometimes the two are not associated. It only takes one unlucky time to cost several hundred if not thousands in repairs.

 

[swick1]

As a professional fungineer I have to agree that taking the ground connections loose is a good idea. It's like wearing a seatbelt. It only takes one crash to permanently screw up your life, but many people still choose not to wear them.