Weatherstrip the Sash
4. Rout the meeting rail.
Place the sash on a padded worktable with the exterior side facing up. Clamp the sash so its meeting rail projects a few inches past the edge of the table. Remove the sash lock and set aside. Chuck the slot-cutting bit into the router and set it to cut 3/8 inch from the router base. (A bearing controls the bit's cutting depth.) Hold the router base firmly against the top edge of the meeting rail and cut a groove from left to right.
5. Rout the bottom rail.
Unclamp the sash, rotate it so its bottom rail is closest to you and overhanging the table, then reclamp. Hold the router's base firmly against the face of the rail and cut a groove from left to right.
6. Weatherstrip.
Press the silicone weatherstripping, barbed edge first, into the groove routed into the bottom rail (below). Take care not to stretch the strip as you insert it. Insert the pile weatherstripping into the meeting-rail groove. Use a utility knife to trim the ends of each piece of weatherstripping flush with the outside edges of the sash.
Install the New Beads
7. Replace the top bead.
Lower the upper sash and measure the length of the dado in the head jamb. Mark that measurement on the shortest parting bead in the kit (above left). Cut it to length. Tap the bead into its dado with the pile weatherstripping facing out.
8. Cut the side beads.
Mark the jamb where it meets the horizontal centerline of the sash's meeting rail (above right). Measure up from that mark to the top bead and down from the mark to the sill. Transfer those measurements to the replacement bead, starting from the bead's center; where the weatherstripping on one side ends and the stripping on the other side starts. (The strips on the upper part of the bead should face out.) Trim the top end of the bead square; trim the bottom end to match the angle of the sill. Repeat for the bead on the opposite jamb.
9. Tap in the side beads.
The fit should be tight enough to hold them in place. If it isn't, drill, then tack the bead in place with a few ¾-inch wire brads. Reinstall the sash, stops, and sash lock. When you're done, the sash should slide up and down smoothly and line up at their meeting rails.
