Quick Boat (not "swift boat" ;) for T-slots.
Grooves hold Cardboard sides.
Definition: A "boat" is used to contain chips when using a milling machine. This makes cleanup after a job much easier.
These two files are mirror configuration that allows you to print out 2 of each. Either the front and back cardboard or the left and right cardboard are cut to an angle of 15 degrees. the other two sides are "proud" of the angled sides. This will let you construct a quick variable size boat for CNC milling. I used these on a Central Machinery #47158 micro mill with a flashcut retrofit and littlemachinery collet set (not shown).
The boat is made to use disposable cardboard sides. You might want make a 15 degree guide for fast cutting the cardboard by hand or on a paper cutter.