Drilling a Square Hole in Metal

Part with square hole

Part with square hole

Drilling a blind (as opposed to a through) square hole in a metal part is a difficult feat. A drill bit will make a nice round hole (or sometimes a not-so-nice round hole), but how can you make a square hole? A broach tool can be used in a drill press to cut a square hole with sharp interior corners, but broaching cannot always be used effectively for blind holes.

Milling a Square Hole

Milling a Square Hole

Typically a square blind hole is machined into a part with a mill, but this process leaves radii in the interior corners… radii which must get larger the deeper the square hole must be. This process can also be very time consuming for manual machinists without CNC capability. And what if you only have a drill press?

Mortiser Bit

Mortiser Bit

It would be helpful if a mortising drill bit were available for metal as they are for wood. With a mortising bit, drilling a square hole is just as easy as drilling a round hole. But this type of tool does not work for metals, only woods.

Here are a few technologies for drilling a square hole with a drill press:

Formbore


Vika, or Watts tool:

The Watts style and Formbore tools use a Reuleaux triangle and bushing to move a cutter along the square path. This video explains how that works:

Here is a great video from an Asian manufacturer with a tool based on the same premise. The tool is not available for your drill press yet, but keep your eye on Harbor Freight:

Happy Machining!

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