I use a motor tool (Dremel) with a fiberglass cut-off disk. Make several light passes. I clean the cut with a coarse metal file.

 

Doesn't the board material dull the file? Does sandpaper work?

 

I use sandpaper and find a low-speed disk sander allows great precision. I use it for final dimensioning and even cut female connectors to size with it.

 

Doesn't the board material dull the file? Does sandpaper work?

Not so you’d notice. Sandpaper will wear quickly

 

I use this sander: https://www.micromark.com/10-Inch-Variable-Speed-Disk-Sander

Bought several years ago for about $110. Not worth current price, but probably a copy is available somewhere cheaper. It goes to a relatively slow speed and disks are easily replaced. Disks last a long time. Don't try to use too fine a disk. It is not hand sanding, and a coarser grit (e.g., 80 to 120 grit) will work just fine. It's the slow speed that give you better control.

 

Yeah, that's pricey. I forgot I have a 1" belt sander in the basement.