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RESTORATION CORNER


REPAIRING BAKELITE CASES


by Jim Foster


Mention has been made in the Telecoms Heritage Journal (UK) that I have become a ‘dab hand’ at restoring cracked and broken telephone cases. Here, for what it is worth, is how I manage to obtain a reasonable, and sometimes almost undetectable repair.

What you need: A small kit of David’s Isopon (or similar - body filler putty we call it), some reinforcing metal mesh, some sheets of ‘wet and dry’ abrasive paper (from course to fine), a can of aerosol spray paint - matt black (no other) All the above items from your local car accessory shop. You also need a mini-drill for 1/32" drills and permission from your better half to borrow the hairdryer. Lastly, a small packet of panel pins.

Cracks only: If the crack extends to the edge of the case, reinforce the crack at the edge with a small strip of metal mesh; across the crack, not along, on the inside of the case and as near the edge as possible. Scratch a hatch pattern with a file tang on either side of the crack where the patch is to go so the filler will form a good bond to the case. Use a small amount of the mix to stick the mesh across the crack and leave it to set for at least 12 hours in a warm room. When it is set, you can tidy it up by filing, scraping or even grinding away any excess.

Next, use a file tang on the outside of the case to make the crack "V" shaped, then mix a small amount of filler, and using a spatula (usually in the kit), work the mix into the crack. Leave it a little "proud". Let it set for 12 to 24 hours, then smooth the repair using the ‘wet and dry’, working down the grades and using plenty of water. Don’t worry about the fine ‘haze’ caused by the abrasive on either side of the crack - this will be eliminated in the final stages. Close your eyes and run your index finger across the repair to detect any difference in levels. This very sensitive digit is capable of detecting a step of one tenth of one thousandth of an inch. When you are satisfied, proceed to the masking and spraying stages, described later.

Missing pieces: If too much of the casing is missing, then you may well be on a ‘hiding to nothing’ in trying to repair it. If however, there are only a few small gaps, then a reasonable repair is possible. Cut a piece of mesh to overlap the hole, and fix as above on the inside of the case. Always ‘hatch’ the area to give the filler a good grip. Leave for 12 to 24 hours before you fill from the outside, and proceed as for the repair of a crack.

Broken edges: It took some time for me to master this technique; simply building up the edge with filler and shaping it inevitably led to it breaking away at the first ‘tap’. What is required is some reinforcement so that the filler gains strength. This where the mini-drill comes in. Make a ‘jig’ of some sort to support the inverted casing, and pad it with foam or sponge. Next, drill a series of holes in the broken edge at approximately one-quarter inch intervals (see sketches). Fit the panel pins into the holes so that they protrude to within one-sixteenth of where the edge should be. If necessary, fix the pins in the holes with a drop of ‘super glue’. DO NOT clip the pins to length AFTER fixing - the force exerted by the pliers or side-cutters when shearing will certainly result in more of the broken edge breaking away. Use a 1/32" drill and panel pins to suit

Build up the edge, overfilling in all dimensions. You may have to apply 2 or 3 layers, but it doesn’t matter if you over fill. Leave each layer to set, the starting with a medium file, take off the excess. Use a straight edge to obtain the correct profile. Do not be tempted to use wood, metal or plastic ‘moulds’ to hold the shape as the filler sets - you will undo all the good work when you attempt to remove the mould. When all is smooth, (check with the finger again), you can prepare for the final stage.

The Paint coat: If for example the damage is on one side of a ‘pyramid’ phone, mask off the other 3 sides (and the cradle if not already removed). Take the masking tape up to the centre of the corners, leaving the whole of the damaged side exposed to the spray. Make the first ‘pass’ with the aerosol along the length of the damage, and immediately use the hairdryer set to moderate. The second ‘pass’ is again along the length of the damage in the opposite direction to pass 1, followed by hairdryer. Once more as for pass 1, then leave it for about 15 minutes. Inspect it. The 3 ‘film’ coats will reveal any real differences in levels, although you still may be able to see where the damage was. If it is obvious that you haven't got it right, use the ‘wet and dry’ and fingertips until you are happy.

Then start again with the aerosol, but this time, continue for up to 12 ‘passes’ using the hairdryer between each coat. Do not be tempted to spray heavily to obtain a glossy finish - this is achieved by other means.

Holes and edges: Use well defined boundaries, don’t just expose the area under repair to the spray. It may mean leaving the whole panel, but the ‘scatter’ won’t cause any problems at the final stage.

Polishing: When all 10 to 12 coats are dry, it will present a surface not unlike black satin, but without any sheen. Use a piece of very fine, worn ‘wet and dry’ and very lightly take off the last coat of paint (microns only!). Dry it with the hairdryer, then use the famous ‘Polishing Paste No. 5’ (‘Shine’ polish or car polish No 2 in Australia) with a fair amount of elbow grease. You will need to repeat this 2 or 3 times, and if you happen to have a buffer pad, you will eventually have a surface which is practically indistinguishable from the rest of the item.

Experiment on a piece of equipment that is beyond redemption, it does take a little practice to get it right, but you will be extremely pleased with the results when you have become a ‘dab hand’.


Article written by Jim Foster in Telecommunications Heritage, Issue 24, 1994.


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