An octagon has eight equal sides.
An octagon has eight sides. You don't need complicated math to draw one, especially if you have established parameters such as a square or rectangular surface. To cut an octagon on a tabletop, or even a blank piece of wood, all you need do is make sure all eight sides are the same length by cutting off the corners. Using basic mechanical skills and a circular saw, you can cut almost any table or panel into an octagonal shape with little effort.
Clamp a straightedge diagonally across one corner of the tabletop or panel. Trace the line on the tabletop. Move the straightedge to the next three corners and repeat.
Measure the eight sides created by the lines. If they're not equal, move the straightedge forward or back and trace new lines. Repeat until all eight sides are equal.
Cut along the lines using a circular saw, keeping the blade just to the outside of the line.
Sand the sides of the octagon flush to the line with a hand block equipped with 100-grit sandpaper if you plan on adding molding to the sides. If you do not plan to add molding, sand the sides smooth and flush to the line using an orbital sander with 100-grit sandpaper.
Use a crosscut blade for the smoothest cuts that don't chip or splinter. Don't use an orbital sander if you plan to add molding. Orbital sanders can round edges and cause dips that interfere with molding placement.
Wear eye protection when operating a circular saw. Keep two hands on the saw at all times. Circular saws can kick back if not properly secured.
Shaddy, Wade. "How to Cut an Octagonal Wood Tabletop." Home Guides | SF Gate, http://homeguides.sfgate.com/cut-octagonal-wood-tabletop-84009.html. Accessed 19 April 2019.