Zero (chip-out) tolerance
How to make inserts fast
You can buy pricey, premade phenolic inserts, but we like to make our own zero-clearance inserts from 3/8- or 1/2"-thick Baltic birch plywood. This stable material proves strong, and doesn't have voids between plies. Medium-density fiberboard (MDF) also makes a good insert, but lacks the strength of plywood. Hardwoods, although strong, can shrink or swell with seasonal changes in humidity, and don't work as well as plywood.
With a pattern bit installed in your router table, use your saw's original insert to make duplicates. Some insert plates have antilift tongues [Photo A] right, or lateral-adjustment screws--with these you need to create a pattern to use for making copies. To do this, trace your insert plate onto a blank of plywood or MDF, smoothing the tongue or screw areas.
Cut close to the line at your bandsaw, and then sand the pattern until it fits snugly into your saw's throat. If you want the antilift benefit of the tongue, you can add this to your inserts by cutting a groove on the bottom side and then gluing in a thin strip of hardwood that protrudes under the tabletop.
Cut out rectangular plywood blanks slightly larger than the pattern. Using cloth-backed, double-faced tape, secure the blank to the pattern, and then bandsaw to within 1/8" of the pattern. Next, rout the blanks to shape using a pattern bit or flush-trim bit in your router table [Photo B] below right.
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