While I try to sand workpieces before they go together, sometimes I have to sand parts after assembling them. When I need to run my sander up against corners in these situations, I cover one of my metal card scrapers with thin cardboard to form a miniature sanding shield. It protects adjacent surfaces from being damaged by the spinning sander pad or abrasive disc. By holding or clamping it in place, I can sand right up to the intersecting surface without negative consequences.
– Willie Sandry