Digital miter-gauge setup
Here's a way to dial in your miter gauge for tricky angles, such as for a seven-sided frame. Cut a piece of 3/4" MDF wider than your miter gauge, as shown. Then center a dado in one face to fit your miter-gauge bar, and add the base, support block, and hold-down.
To set an angle, insert your miter gauge into the jig, stand the jig on end, and zero a digital angle finder (such as a Wixey; Rockler item no. 27487; 800-279-4441; rockler.com) on the face of the miter gauge. Loosen the scale on the miter gauge and tilt the miter-gauge head until the angle finder reads the desired angle. Now tighten the gauge and start making uber-precise miter cuts.
— Bob Wilson, Urbandale, Iowa