Repair for Air Ministry Bakelite Instrument cases and similarly damaged Bakelite components.

[Shakydoo]

Repair for Bakelite Instrument cases/switches/fuse boxes/connector blocks; broken mounting lugs and similarly damaged Bakelite components.
Bakelite is a thermosetting phenol formaldehyde resin; a combination of phenol, formaldehyde, and wood flour. The mixture is put under pressure, and after curing, forms a hard plastic material. Repairing Bakelite is one of the most difficult tasks to accomplish successfully with common adhesives.
Broken mounting lugs are the normal damage found on these components and can be rectified by the following repair procedure...

Plasticine is used to make a mould, using a good corner (or similarly-profiled section) of the damaged component as the master pattern.
This good corner is pressed into the Plasticine block to leave a master impression for moulding the damaged area.

The component is then carefully removed and small, angled holes are drilled laterally into the damaged lug area, into which, fine copper or steel rods are inserted to reinforce the area to be moulded from the master impression. Position these reinforcing rods so that the ends do not encroach any component mounting holes.
The drill size is usually 1.5 - 2 mm, depending on the thickness of the damaged lug; and a drill held in a pin vice rather than a powered tool is recommended.

The component is then carefully fitted into the plasticine mould with the broken section located into the master impression.

Slow-setting Araldite epoxy resin... (Araldite ARA400001 Precision grade epoxy resin is preferred)... is mixed with Bakelite filings from a similarly-coloured scrap piece of Bakelite, and introduced into the mould void, slightly overfilling to allow for final shaping and finishing.

The Araldite epoxy resin/Bakelite mix will flow more successfully if gentle heat is applied as the void is filled.

When set... allow at least 24 hours undisturbed; carefully peel the Plasticine mould away, and trim up and shape with scalpel and fine files.

Finish with a fine-grade wet and dry paper.

Broken and missing segments of other Bakelite components (Trim wheels etc) can be rectified by the same procedure; as can steel and aluminium components; replacing the Bakelite filings with cast-iron filings for steel components, and aluminium filings for aluminium components.

The instrument illustrated is a non-radium-dialled example. Suitable safety and handling precautions should be observed during dis-assembly if the instrument to be rectified is radium-dialled.

[Adrian Stevenson]

Very useful guide. Thanks.