Cutting an Octagon Hole

Another quick shop hack from our builds. You can do this with a drill and a jigsaw.

Five-step guide to cutting octagon holes in a 1.5 in board

Animation of laying out and cutting octagon holes in a board

1. Lay out the octagon. Side length = flats x tan(22.5 degrees): 6 in hole has 2.49 in sides, 12 in has 4.97 in, 18 in has 7.46 in.

2. Drill out each corner with a 1 in Forstner bit or hole saw, just inside the lines (a 3/4 in bit works for the 6 in hole). Drill from both sides to avoid blowout.

3. Connect the holes with straight cuts: a jigsaw along a clamped straightedge, or a router with a straight bit and edge guide.

4. Cleanest on 1.5 in stock: clamp an MDF octagon template and use a plunge router with a pattern bit in shallow passes, about 1/4 in each.

5. Finished holes. Corners are slightly rounded to the bit radius.