Tuesday, 13 January 2009

How to Install Threaded Inserts

Threaded inserts are fastener-related devices constructed of metal or plastic materials. They are generally used to provide thread tracks for screws or bolts. These inserts can allow a fastener to form a more secure attachment to soft or pliable surfaces that would otherwise reject fastening, repair a damaged thread track, or install threads into a workpiece without relying on a more elaborate production process. Threaded inserts are usually placed inside an existing hole or slot, and they feature an external design that allows them to be lodged securely, along with a cylindrical inner cavity lined with threads.

Fastener inserts can be made from a wide range of materials, including metals such as brass and steel, and plastics such as PVC. Likewise, they are available in a variety of design types depending on their application. Molded inserts are used in plastic fabrication cavities, while key-lock inserts are employed for repairing stripped thread holes. Threaded brass inserts are most often used for fastening plastic materials, although they can also be applied to wood and other surfaces as well. Installing these inserts is usually a multistage process, and can sometimes require special equipment or techniques to accomplish.

Threaded Inserts in Wood

Installing a threaded brass insert into a wood surface requires a certain degree of care. A threaded rod with a length depending on the specific application needs will be required, along with a few similarly-sized nuts, masking tape, and copper tubing with an internal diameter slightly larger than the external diameter of the threaded rod.

First, a pilot hole must be drilled into the wood at the point where the threaded insert will be installed. To help keep the angle of insertion perpendicular to the surface, it can be helpful to mount the workpiece in a drill press, but it is important that the drill press is off during the procedure. The workpiece should not be clamped too tightly because the threaded rod should be able to rotate inside the copper sleeve. The rod can then be twisted into its slot with a wrench, while masking tape is used to keep it from slipping out of the copper tubing, which functions as a sleeve. Depending on the hardness of the wood, considerations may need to be taken for clearing chips from the area.

Threaded Inserts in Thermoplastic

Putting threaded brass inserts in a thermoplastic material, such as acrylic, involves a different set of equipment and methods than those used for wood surfaces. In some cases, the insert may need to be melted into the workpiece in order to form a secure joint. Generally, this occurs on the more rounded side of an acrylic piece as a smaller amount of melted plastic will gather near the insert and the installation will be easier. The standards steps in such a procedure include:

• Positioning: A threaded brass insert usually has a taper on one side to help with insertion into a slot. Inserts should be placed along the surface of the thermoplastic workpiece in their intended spots, ideally along a series of predrilled holes.
• Insertion: The workpiece should be clamped or moved to ensure that the insert holes are overhanging the edge of a bench or other work surface, and a heated soldering iron may then be pressed into the threaded insert. Applying a slight amount of pressure onto the soldering iron will help push the insert straight down into the material.
• Protrusion: The soldering iron can be used to guide the insert and keep it straight as it enters the workpiece. The insert should be pushed until it lies flush with the top surface of the workpiece, although there may be a small accumulation of melted plastic that rises over the insert. Depending on the application requirements, the insert should also be checked to see if it lies flush with the bottom half of the plastic surface.
• Inspection: After the threaded insert has been installed, it may be helpful to use a screw or bolt to verify its positioning. If the screw attaches at a bent angle, the soldering iron can be applied to reposition it correctly.

It may be necessary to preheat an insert on the soldering iron before beginning installation, especially if working with a large brass insert. Alternatively, a drill press can be employed to grip the workpiece while heat is applied to the insert, although the press should not be turned on during the process.

Ilya Leybovich
ThomasNet.com Staff Writer

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