I was rewiring a Singer button controller today and when I was reassembling the bakelite housing, it occurred to me that the steps I take for granted may be be worthy advice to share with others.
Bakelite is really a “plastic” used from the mid 1930’s well into the early 60’s. And like any plastic, it is much softer than steel and can crack if proper care isn’t followed when reinstalling the steel screws. When it comes to reinstalling the screws, the consequences of cutting new grooves instead of mating with the existing grooves (cross threading) the screws will result in catastrophe, frustration, and tears. The damage caused by cross threading plastic is often irreversible, and even in the best case, weakens the grip of the screw.
To illustrate what I mean, the next few pictures show how this controller is disassembled… and of course, reassembly is the reverse in order of the disassembly.
Note that the metal screws tap into the bakelite housing. The threads it cut in assembly must match the screw threads in the same grooves when it is reassembled. The steel screws are very capable of cutting new grooves in the bakelite housing when reinstalled and this will damage the bakelite housing, bind when tightening, and will likely break or crack the housing. This is true of all plastic housings so this advise spans any application where plastic is fastened with screws.
Prevention is simple. It is easy to align the steel screw threads with mating grooves in the plastic… When you set the screw in the hole of the part to be reassembled, don’t start by turning the screw clockwise (tightening). At this point, you can’t feel where the threads of the screw and the grooves in the plastic mate. Instead, start by turning the screw counter clockwise (loosening) while gently applying downward pressure to the screw. Usually, the weight of the screwdriver is enough. As you are turning the screw counterclockwise, you will feel the screw “set” and the first thread of the screw will settle in the first groove in the plastic. At this point, proceed to tighten the screw. it will not try to cut new grooves (cross thread) but will follow the existing grooves and tighten smoothly.
Its simple, dependable, and will prevent damage to the plastic part being reassembled.
I hope this helps!