Drill out the bad threads using the drill size specified in the Helicoil manual. This will allow you to re-tap the hole for the threaded insert. Line the hole up with the manual or CNC mill and carefully drill the hole on center. Use a dial indicator to find the center of the hole.
Tap the new hole using a Helicoil tap. Helicoil-threaded insert sets usually include a tap of a specific size for the tapping process. Attach the tap to a tap handle and hold the part in a vise. Carefully tap the hole in a clockwise motion. You can also use a tapping head on a manual or CNC mill to tap the hole. Tap on center to avoid tap breakage.
Screw the Helicoil insert onto the Helicoil installation tool. Pull the threaded rod out and place the Helicoil in the chamber. Slide the threaded rod down into the Helicoil until the tang rests in the slot, at the base of the rod. Carefully screw the Helicoil into the threaded base of the plastic chamber until it pokes out the bottom slightly.
Place the bottom of the installation tool over the thread. Slowly turn the installation tool's crank clockwise until the threaded insert catches the thread in the newly tapped hole. Crank the handle until the threaded insert releases from the bottom of the tool. Make sure the insert is at least 1/4 turn below the surface of the hole, preferably 1/2 turn.
Break off the tang at the bottom of the insert. Place the tang break-off tool on the tang itself and tap the top of the tool with a hammer sharply. This will break the tang off and allow you to screw your bolt or screw below that point if necessary. If you are using a short screw or bolt, this step is not necessary.
Repeat steps 1 through 5 to fix other holes that have damaged threads.Manufacturers are painfully aware of expensive mistakes when cutting threads. It often means consigning an expensive part to the scrap heap. Helicoil- threaded inserts help eliminate this issue, repairing damaged threads while also providing an a maximum-strength threading alternative for soft metals like aluminum.