I recently spotted this battery driven pencil eraser in Hobbycraft. It’s about the size of a fat marker pen and has a simple friction chuck to hold small sticks of eraser material.
The chuck is simply pulled out, and the eraser pulled from the chuck.
I’ve been using Garryflex abrasive blocks for a while for sanding irregular surfaces – these are a rubber-like material impregnated with abrasive grit. They are relatively soft and can be cut into smaller bits easily with a hobby knife.
I cut off a 5mm slice from the end, and then cut that into 5mm sticks. These sticks can then be inserted in the eraser chuck. Although they start square, the soon wear down to a rounded point.
The tool can then easily be worked into tight corners and concave surfaces that would otherwise be hard to reach with sandpaper. Here’s an example wornking on a filled seam on the Moebius Invisible Man kit.
Note: Always wear eye protection because particles of grit can fly out in all directions as you work!