Burn streaks on the work

[Sunset Machine]

Operation is pretty simple, just practice rubbing your tummy and patting your head - but it's the wheels that throw me. Each grit size comes in 26 levels of hardness and a bunch of different binders and types of grit, and I'm a-thinkin there's a reason for each. For example, the wheel in the photo produces a nice finish on structural steel that I use for fixtures & spacers, but it's failing miserably on the chuck. Which wheel to use is always the question.