[MRM]

The rule is to dress one level higher than the regular clothes you will be expected to wear at the job. In this case that means your idea of a tie and jacket but not full business suit is very much the way to go. If you showed up in a full business suit they would think you were too stuffy to get your hands dirty. If you don't dress up at all they'll wonder why you don't respect them enough to fress up for an interview with them.

Dress like an engineer. You know what I mean. Sport coat, blue button down shirt, red tie and loafers or similar shoes.