Intro: Drill Square Holes With a Bridgeport or CNC
The tool used for making hex and square holes on turning machines is called a Rotary Broach.
The system requires two components, a broach holder and a broach.
Select the broach which is the same size as the hole you want to make.
The broach holder keeps the broach on center at the cutting edge, but at a 1 degree angle to spindle.
The angle causes the broach to cut only the corner closest to the part.
As the part or the broach holder are rotated, each corner eventually becomes the cutting edge.
Feed the broach through the pilot hole while turning, and the full form will result.
Basic steps for setting up a rotary broach:
1. Pre-drill a pilot hole larger than the minor diameter of the broach, and deep enough for chips to accumulate.
2. Add a chamfer larger than the major diameter of the broach.
3. Feed the broach through the hole while turning.
(In a lathe, the material will turn the broach. In a mill, the broach holder turning in the spindle will make the broach rotate.)
4. Chips can be drilled out or left in the bottom of blind holes.
Rotary broaching tools can be used on Bridgeports and CNC machines.
The broach holder used in this video is made by Polygon Solutions Inc.