Using the Hollow Square Punches
Before starting give the punch a good sharpening. The sharpening cones available at Lee Valley are the correct angle for the inside surface.
Layout the location for the square hole.
Using a small square, center the punch on the layout.
Now lightly tap it in place to registers its position. Often the punch will stay put when you remove your hand – if not it is easy to relocate.
Now, using a bit that is 3/64″ under the size of the square hole (3/8″ square hole – use 21/64″ bit), drill out the center. Use an ordinary twist bit for this and not a brad point. The leading sharp corners of the brad bit will catch on the inside of the chisel and damage themselves.

Remove the punch for a perfectly square crisp hole!
The Hollow Square Punches will be available from Lee Valley Tools very soon.
Use the product code 50K5920.
For more on the Hollow Square Punches see my previous blog.