I certainly did not want to replace the motor, as this is so very visible, all attempts at maintaining the illusion of originality would fail. A solution to the problem could only be achieved with a safer, replacement speed control, which could work with the original mains voltage motor.
Fortunately, these are readily available in the form of a Pulse Width Modulated (PWM), motor speed controller circuit. These will take in the 220V incoming mains supply and provide a variable output of between 50V and the incoming supply voltage. These are well known devices and proven to work with even simple (old) motors.
So, a PWM circuit was obtained (at incredibly reasonable cost), and measured up.
In an attempt to at least have the "illusion" of originality, I was determined to use the original hole for the rotary speed control, as well as the original Bakelite control knob. With the shaft on the rotary potentiometer too short for this, I had to do some more metal bashing.
As can be seen below, I used the old rheostat as a donor, for a short length of it's shaft, which I would mate to the new potentiometer, allowing the Bakelite knob to operate. This was cut to shape and filed to mate with the new potentiometer shaft. This was then soldered together and thus ready for installation.
You can see in the photo, the size and technical comparison between the old rheostat and the new PWM controller circuit.
Next up is the motor speed control.
I did think long and hard about my original aim of maintaining as much originality as possible. And, there is no doubt that the original speed control rheostat was a) original and b) functional. But - as I was an electronics technician in an earlier life, and also health and safety professional in a more recent life, the safety aspects weighed heavily upon my concience.
Logic played it's part as well - with the original rheostat put back into service, albeit with some hand-made guarding to keep out the fingers of the unwary, it would be safe-ish, for me to use, as long as I kept my wits about me.
BUT NOT SAFE FOR ANYONE ELSE unaware of what was underneath.
Only the knowledge of what lurked underneath would be keeping me safe, but anyone else might not have a second chance.
As can be seen from the photo below, all of the wire on the resistors is not only unguarded, but within millimetres of the level of the base. Also, the incoming mains terminals to the rheostat are also dangerously unguarded.
With today's knowledge, it is difficult to fathom how this ever could have been considered safe to use.
Back to the job in hand.
I managed to find the cork I thought I may have had, lurking in a box under the stairs. It was the most part of an A4 sized sheet, so more than enough for my purposes - to sit the jars on whilst they are in the machine.
Looking at the metal bases, I really can't be convinced if there ever was any cork or any other material for that matter there. But for me anyway, the idea of the glass jars sitting directly on the metal base just seems wrong and I would prefer some cork there as a cushion.
It's about as tidy as it needs to be, given the shape of the metal webbing. I suppose I could have cut-out squares of cork, but then it would leave potential weak, unsupported areas of cork, which would likely need some form of strengthening.
Anyway - this application suits me and helps the jars sit a bit more stable in their locations.
Whilst I am in the vicinity, so to speak, I have also added an earth lead which will bond the chassis to the incoming mains lead, once fitted. This is visible in these photos.
A little further research and then on with the show...
A quick browse through patent databases, shows that one Saul Lanzetter applied for and was awarded a patent for this design of watch cleaning machine in October 1937. A brief narrative is reproduced here:
Interestingly, the patent application is entitled "Improvements in apparatus for cleaning watch parts and other small parts of machinery."
It may be reading too much onto this title to assume that there may have been a previous patent, pre-dating this one, as this one refers to "improvements".
Also of interest, there were 2 patent applications from US companies in 1944 and 1945 which cite the Lanzetter patent, and three from Germany in 1956, 1960 and 1961 (only one of which was actually published), which also cite the Lanzetter patent as a reference.
Incidentally - the two US patents refer to machines which look strikingly similar to the National Model VI-C above, and the National No 4. machine in the earlier advert, showing the four jars side by side ( this seems to be referred to as a lab machine, rather than a repair shop machine).
Naturally, all patents or applications referred to above are now expired.
For me anyway, I think this may clear up which watch cleaning machine may have come first (at least in this machine format anyway): The S. Lanzetter National Electric Watch Cleaning Machine, circa 1937.