Today I needed to file a bevel on a lock plate that I am getting ready to inlet. I thought I would share a couple of photos of a simple fixture I made many years ago to aid in holding a lock plate, side plate etc. for filing bevels. I used a scrap piece of hard maple 2" square by 7" long to make the fixture out of. The beauty of this tool, besides its simplicity is that it can be clamped in your vise jaws in 45 degree increments and can also be held horizontal, vertical or any other position.
If I get ambitious, I may mill a new one out of aluminum, that way I could drill and tap holes as necessary to help clamp items to the fixture.
David