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Restoration/ Repair of an Eureka Battery Clock
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Restoration of a Eureka Electric clock
The Eureka clock was designed by T Powers an American engineer and patented by the Kutnow brothers in 1906. The saying is that only about 10,000 clocks were made and because of this prices have risen considerably over the years Many articles have been written on the Eureka clock, the one to get is by Dr Alan Shenton published in 1979 it contains technical details, patent specifications, and the history of the Eureka
Clock, plus details of the various models that were for sale.
These Eureka clocks were expensive to buy in 1909 when you consider the average wage for a working man was 28shillings to 35s a week, ( £1.40 to £1.75 ) the average price for one of these clocks was £5.00 and the most expensive was the Cromwellian model selling at £10.10shillings
Let me say at this point these clocks are designed to run on 1.5 volts I have had clocks coming into the workshop with 9 volt batteries connected!! If it doesn't work on 1.5 volts then it needs a service take it to a competent repairer, increasing the voltage is not the answer .Originally these Eureka clocks had a large Leclanche type battery which would last 3 years ( no longer available )
nowadays a good "D" cell battery like Duracell MN1300 or LR20 should be used. The current drain is about 1.50 milliamps so the battery will need to be changed about every 4 to 6 months, you could, if space permits, use two batteries wire up in parallel. which would still give you 1.5volts but last a little longer.
The movement on the first Eureka clock had suffered badly over the years, both the contact spring and stiffening spring were missing New ones were made with the use of a jig that I had made for a previous repair.
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You can see the new spring fitted in the jig ready to be filed to shape, the punch below is used to punch out the holes for the retaining screws
It is important that the spring and flag are made the correct length or contact with the silver pin will be in the wrong place and impulse to the balance will be poor.
Contact should take place about 30 deg. before the vertical and cease immediately before reaching the vertical position. Another important point to note is the contact pin on the balance wheel, it's quite complicated, half the pin is made as a conductor( silver) and half an(
fibre)
insulator. It works like this--when the contact pin is rising it passes on the inside of the flag and contact is made on the silver half of the pin energizing the electro-magnet and giving impulse to the balance, when it's falling it passes on the insulated side of the pin so no current will flow. If it does it will have a braking effect on the balance and the clock will stop!! You can test
this by connecting a voltmeter across the battery, the meter should show 1.5 volts with no movement on both swings of the balance wheel if it does check the insulation of the silver pin for shorts.
If there is the
slightest hint of oil on
the contacts it will increase the contact resistance which in turn will reduce the current to the clock, making time keeping poor! most of the Eureka's that I've seen have for some reason been oiled here and it has soaked right through the fiber insulation, rendering the whole thing totally useless! I would add at this point that new contact pins and flags are only made
if the old set can't be repaired, I like to keep movements as original as possible.
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The new contact spring, final adjustments are made by filing the flag to give correct timing and impulse to the balance. Some Eureka clocks have elongated holes for fixing the contact spring to the block (which makes setting up a little easier) and some are fixed, also some of these clocks have a second stiffening spring fitted to give a firmer contact to the silver pin, the thickness of the spring should be 0.004"
I have been experimenting over the last few months to make a suitable, robust insulating piece to hold the silver contact pin, this is the result and it seems to work well.
It's made from hard plastic and turned on the lathe (hard plastic knitting needles are very good!) or you could use any hard insulating material.
First centre drill your hard plastic rod to slightly smaller than the silver pin you will be using,( 18 SWG Sterling silver) then turn down the rod to as near the hole as possible, this then is filed to half it's diameter which will expose half the silver rod when fitted. File the lead "in" and "out" edges of the plastic half of the switch to aide smooth contact with the flag as the balance rotates.
Make the second cut to fit the diameter of the hole in the brass mount which holds the balance arm,( the diameter of this hole seems to differ from clock to clock!! so
each one is cut to suit the hole in the brass mount.) trim off and polish up the plastic and there you have it! Needless to say it must be fitted correctly along with the silver flag so impulse to the balance takes place at the right place and time,( the contacts are only closed for about 60 milliseconds so it becomes important to set up correctly!)
This is the finished contact switch fitted in the brass mount.
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make the diameter of the FINISHED SWITCH as small as possible- it will reduce drag on the flag! |
This switch came from a Eureka clock that had been "repaired" needless to say it didn't last long and as far as the customer was concerned his money spent was-- money down the drain! |
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Now lets look at the mechanics of the Eureka. On the balance wheel is a fixed eccentric cam and as the balance rotates this cam pushes on a roller, on this roller is a lever at the top of which is a pawl which pushes the ratchet wheel forward one tooth on each swing of the balance and though a series of wheels drives the hands.
An overall picture of the impulse arm
The pawl is gravity operated between two fixed pins positioned on the clock frame. The wheel needs to rotate very freely on it's
arbour i.e. no tightness
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This was the condition of the balance spring as taken from the balance wheel. I have repaired them in the past but this was a little to far gone, with the coils out of true and touching it would only give poor time keeping so it was decided to look for a new one. That I though would not be easy but I had a little luck when I talked to a friend of mine Richard Charman who runs Clock Spares of Dereham in Norfolk,
he has many old clock parts I know but it was a pleasant surprise when he said he had one. With the new spring fitted and the contacts repaired the amplitude of the swing went from 180 deg. to 356 deg. anything below 300 deg. is not good and with the battery disconnected the clock should run for at least 3 minutes unaided.
The new balance spring fitted on the old collet
If you have one of these clocks you would like repaired or one you want to sell then phone me on 01359 269601
I DO HAVE A FEW SPARES FOR THESE CLOCKS-CLICK
HERE
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This is a picture of the balance, with the bobbin shown in the middle, it was found
that the enamel insulation had broken
down on the copper wire giving a very low reading on the ohms meter, the only answer was to rewind it.
I have rewound several coils over the years (not a easy job) the copper wire should be 30swg 0.315mm and when the bobbin is full
will
give a reading of
about
21
/24 ohms, before starting to rewind make sure the copper wire is firmly attached to the iron bar or the coil will be "open circuit" and will not work
It is important to have the balance wheel correctly at balance--hence the
word balanced wheel, meaning a wheel that is balanced!! This may be
stating the obvious but I see clocks in the workshop with lumps of lead and
brass added-- apart from looking terrible it doesn't work and adds to the
battery drain.
This is a poorly balanced wheel with added brass
weights -ugh!!
TO BE CONTINUED WHEN TIME PERMITS!!
Eureka clocks
These pages will be updated and added too as time permits
Last updated 13 May 2006
go to---PAGE TWO
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If you would like to see more pictures of
other styles of Eureka clocks CLICK
HERE
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