peek plate with brass threaded insert visible

Novena Heirloom – Threaded inserts

The composite material developed for the enclosure and LCD panels of the Heirloom is very strong and light in weight, and has excellent impact resistance and interesting thermal and acoustic properties. But it cannot hold threaded fasteners the way something like a plywood construction might. So I looked a variety of threaded insert designs and worked out a process for installing them.

Threaded brass insert
Threaded brass insert

There are a variety of styles of threaded inserts for different applications, none of which exactly match this one. But after a bit of consideration and a few trials, a particular type of threaded insert designed for molding into molded plastic parts proved to be the best candidate.

Coupling used to set up insert milling operation on CNC mill
Coupling used to set up insert milling operation on CNC mill

This style of threaded insert has a knurled exterior surface. The Heirloom installation entailed the milling of stopped holes into the composite that are slightly undersized for the insert outside diameter. The inserts are then coated with one-part urethane adhesive and gently pressed into the composite, snapping past the veneer/fabric layers and into the cork below. Because of the aggressive texture of the knurled, threaded insert and the relatively high porosity of the cork, the urethane’s natural foam-and-expand action permeates both surfaces and produces a very successful bond.

Loose and installed threaded inserts
Loose and installed threaded inserts

In the case of the peek plate mounting in the bottom of the enclosure, the withdrawal strength requirement is not particularly high. Because there are a relatively high number of threaded inserts being used to mount a pretty rigid panel, the completed assembly is quite strong.

A similar use of these brass threaded inserts is on the rear panel assembly that carries the speakers and the PCBs for both the speaker connection and the switch mechanism. The only difference between the two applications is that the threaded inserts are flush-mounted on the rear panel and installed slightly proud to serve a secondary function as stand-offs in the case of the peek panel.

 

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Part 2 will describe the aluminum threaded inserts seen mounted in the black peek plate at the top of the post.

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