Repairing threads

In cases where the hole diameter has been enlarged substantially, such that thread repair with helical inserts is no longer possible, we will need to use inserts that are thicker but can bring a hole to its original size. 

These are known as threaded inserts, and are commonly thick enough to have both internal and external threads. They resemble solid bushings but with the ability to lodge themselves into holes that may or may not be threaded before installation. There are many types of threaded inserts, and their designs differ depending on the application. In this section, we will look at key-locking inserts.

Key-locking Insert

Key-locking inserts are characterized by their resemblance to bushings but with internal and external threads and cutting slots. Being extremely strong, these inserts are used to create wear-free, vibration-resistant screw joints with high loading capacity in materials with low shearing strength. Critically, they are extremely useful in environments with high vibration which may cause other types of inserts to become loose. They are suitable for installation in the following materials: Light Alloys and Cast Iron.

Key-locking Insert Installation

To use key-locking inserts, it is necessary to drill the hole to the correct diameter, followed by tapping with a standard tap. Using key-locking inserts requires a drill bit, a tap wrench and tap for hole preparation, and an inserting tool for installation.

1. Drill Bit A drill bit with the correct dimension should be used for.	2. Tap Wrench A tap wrench for hole tapping	3. Standard tap It is recommended to use a standard tap before installation	4. Keylocking Insert Installation Tool

Key-locking Insert Repair Process

The process of Key-locking thread installation involves 4 major steps. They are listed below. 

	Assessing the hole Check and assess the parent material and hole to be repaired. Important: as key-locking Inserts need a larger than normal hole diameter, make sure there is sufficient space allowance for drilling.
	Drill  Using a power drill or drill-press machine, drill the hole to the correct diameter.
	Tapping the hole Using a standard tap, tap the hole to the correct size and tolerance.
	Turn the insert into the threaded hole by hand Turn the insert into the hole by hand in a clockwise direction. The correct depth should be when the insert is flush with the surface and only the kees are protruding.
	Installation Using the installation tool, knock the keys of the insert into the work piece until they are flush with the surface.

Troubleshooting

In the course of using key-tapping inserts, there are some important points we need to take note of to ensure smooth installation. Below, we list some common mistakes that occur and the steps to take in order to prevent them.

1. While installing, the insert is not able to enter the threaded hole.

Corrective action: Make sure that the hole is drilled to the correct diameter*. When installing, make sure the insert is held in place by the collar and sits vertically on the hole before turning in. 

For screw-lock inserts, it is important to use prewinder-type tools, as the hexagon coil needs to be compressed before it can enter the tapped hole.

*Do not use standard drill charts for standard taps. Key-locking inserts utilize a different set of drill sizes altogether.

2. After installation, my work piece breaks. 

Corrective action: Check that there is sufficient space allowance between the hole and the edge of the work piece. A self-tapping insert needs enough space to sit in. Also, check on the brittleness of the parent material. 

Frequently Asked Questions (FAQ)

1. When should I use key-locking inserts?

Answer: When the damaged hole has been too enlarged, and usage of helical inserts is no longer possible. They are also applicable in environments where heavy vibration may cause the screw or insert to be dislodged.