Mortising Sharp Inside Corners on CNC Equipment

A few suggestions for making inside corner cuts with a CNC machine. April 6, 2007

Often I am asked to cut grilles or grids from MDF or solid wood, the criteria being that the corners are as small a radius as can be so that the hole would resemble more of a square. I perform this task on a CNC router using a 1/8" spiral making one to two passes to complete the cutout. Because the tool is so small, I have to use a slow feed rate to keep from breaking the tool. Does anyone have recommendations on how to do this better?

Forum Responses
(CNC Forum)
From contributor F:
Why don't you cut the slot with a larger diameter tool, then come back with the small tool to just to clean out the corners? On some details, I come back in with a 1/16" diameter bit to do the cleaning out. Better than a chisel.

From contributor W:
I agree with contributor F. If you must make the grille out of one piece, I sometimes will dado a piece of wood or MDF on the CNC, then cut into strips on the table saw so they half-lap together. You will get square corners that way; a little bit more time, though.

From contributor M:
A few options depending on the size of the slot and equipment.

1- Drill a small hole in each corner of the slot and then rout it. The drill will provide the small radius, but it is stronger drilling than routing with the small diameter.

2- After routing the slot, drop a saw blade in and square up the corners.
3- There is an aggregate which holds a milling cutter and is commonly used in door cutouts.