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The Anniversary Clock Project.


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A couple of days ago, the boss and myself went to look through the junk in an old shed that's on a site we have with a view to keeping anything worthwhile before it's demolished. Sitting on an old table, covered with dust, I found this 'Bentima' anniversary clock. The guv'nor said I could have it, and I intend to use it as project when the wife goes to Oz in a few weeks time. The reason I wanted it was that it's a mechanical clock, not one of the more modern quartz ones. At first, I thought the suspension wire had broken, as the pendulum bobs were sitting on the base, but it turned out it had just become unhooked. What was obvious, was that it was overwound, or wound to the point where nothing was working. Using a small tap wrench, (as there was no key...one has been ordered fom Cousins) to ease the pressure on the click spring, I held it off the pawl with a screwdriver and let the mainspring down. With the hands and dial removed, I eased the backplate slightly, and after adding a little tension to the spring, lo and behold, it started to work. All I can assume is that the old oils had gummed up, and releasing the plate allowed enough play to set it in motion again. Once I have the new key so that I can safely play with the barrel and mainspring, I'll strip the whole thing down, clean all the bits and relube. Will keep you posted. Haven't done any clock work since the 'Grandfather Clock' project back in 2010, so will be interesting.

Pretty sure this is a fairly cheap clock, I've never heard of the make Bentima, but will be a good exercise in clock tinkering.

Anniversary clock

Anniversary clock

Anniversary clock

Hands and dial off...

Anniversary clock

Anniversary clock

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I knew I should have put this away until madam goes away, but curiosity got the better of me and I started to strip the clock down. The first thing I found was that although the suspension wire for the pendulum isn't broken, it is rather bent and kinked in a couple of places, so out with the verniers and 3 new wires  (they come in 3s) of the correct dimension (0.0023", 0.058mm) have been ordered from Cousins. These are Horolovar temperature compensating wires made of Nivarox, so should be superior to the one fitted. It will be a case of removing the top and bottom fixing blocks and the verge fork, very careful measuring and then reassembling on the new wire before cutting to length...the wires are supplied over long.

Anniversary clock

The base, which in the original pics above appeared pitted and rusty in places cleaned up really nicely...the marks were in the laquer coating. This was cleaned off using Solvol Autosol, polished and will be re-laquered when I get some. The dark marks are reflections of my whiteboard (on the top) and stuff on my bench (on the sides)

Anniversary clock

I won't take the movement apart until the new key arrives and gives me more control over letting down the barrel and mainspring.

Anniversary clock

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Dear Roger, that sounds like quite a project - anniversary clocks are notoriously finicky before they will run properly. As for Bentima, this was a perfectly decent British clock brand, based at 18 Bury Street, London. The company seems to have been mainly a retailer of clocks made by others - imported and domestically made. However, the firm does seems to have had a manufacturing interest, with a factory in Perivale and links to the Perivale Clock Manufacturing Company Ltd.. Bentima was mainly involved in the production and marketing of mechanical clocks but also made or produced electric examples, including an all-electric Westminster chime model launched in 1953 and hailed as being revolutionary. The firm was a competitor of Smiths and seems to have been in operation from just before/after World War Two through to the 1970s. The ultimate fate of the brand seems to have been acquisition by Acctim, and quartz clocks designated as "Acctim Bentima" are current products.

I wrote a short topic on watches marked, "Bentima" here on the Forum back in March 2014, and I suppose I should really write something on the clocks. There is some information about Bentima online, though it is a bit scattered and could do with collating, expanding and updating. For example, even the exact dates for Bentima are not clear. As for anniversary clocks, I also wrote a topic for this Forum about their history.

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Thanks for the info, @Always"watching". You are correct in the fact that these clocks are notoriously difficult to set up, Honour...just levelling it with the 3 adjustable feet will test my resolve...and this has to be done for every new position you might move it to, to compensate for out of level shelves or mantlepieces. Regulating is a challenge too...there is a screw that adjusts the balls on the pendulum in or out to either speed up or slow down the rotation. All good fun!

Interesting that while you say Bentima is a British make, the dial says 'Foreign' at the six position (see pic above), unless that just refers to the dial.

Edit: Just had a look on Google, and the model I have was made in Germany for Bentima by Kerne and Sohne...this is born out by the logo on the back plate. I'll take some pics tomorrow.

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45 minutes ago, simon2 said:

What is the condition of the mainspring. Is it " Set"??

I managed to let it down, Simon. It was so tight that nothing would go. After releasing the tension, the movement did function when I applied a small wind to the mainspring...this will be evaluated in the coming days. As you may have seen from the above, the suspension wire has seen better days, and I'm going to replace it with a modern alternative.

 

 

23 minutes ago, WRENCH said:

@Roger the Dodger. I remember a neighbour having a Bentima 400 day Anniversary clock that looked similar, is this the same type ?

I can't tell you this, ol' pal, cos you haven't posted a pic for me to compare it to, but judging by my Google search, it's a fairly common model.

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14 minutes ago, Roger the Dodger said:

can't tell you this, ol' pal, cos you haven't posted a pic for me to compare it to, but judging by my Google search, it's a fairly common model.

I'm going from memory here. It looks the same. It was explained to me it had a torsion spring, and only required winding every 400 days, and that's about all I can remember from 40 years ago. Oh, and the owner was a dentist.

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On 28/07/2018 at 23:12, WRENCH said:

I'm going from memory here. It looks the same. It was explained to me it had a torsion spring, and only required winding every 400 days, and that's about all I can remember from 40 years ago. Oh, and the owner was a dentist.

The torsion spring is the suspension wire. It's flat like a ribbon, and as it twists back and forth via the rotating pendulum, it moves a fork attached to it near the top left and right, which acts on the verge, a pin extended from the pallet fork. This allows the pallets to move back and forth and release the power from the mainspring via the escape, thus driving the movement. It's similar to the the pallet fork and jewels in a watch movement, but much, much slower. That's why these clocks can theoretically run for a year, and where the name 'anniversary' clock comes from. While researching, I came across a clockmaker who recommended that the clock is wound monthly because if left for the year, the tension decrease in the mainspring can cause timekeeping innacuracies.

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Dear Rog @Roger the Dodger, just to say that I did mention in my post above that Bentima was primarily a retailer of clocks, and that some of these were imported. I should have really gone on to mention that most mechanical anniversary clocks sold in Britain by British retailers, including your own, were imported from Germany. As I carefully stated, the Bentima concern was essentially a "brand" rather than a "maker," but does seem to have had some involvement in clock manufacture. Good luck with the clock, and let us know how well it keeps time over a longish period.:biggrin:

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27 minutes ago, Always"watching" said:

Dear Rog @Roger the Dodger, just to say that I did mention in my post above that Bentima was primarily a retailer of clocks, and that some of these were imported. I should have really gone on to mention that most mechanical anniversary clocks sold in Britain by British retailers, including your own, were imported from Germany. As I carefully stated, the Bentima concern was essentially a "brand" rather than a "maker," but does seem to have had some involvement in clock manufacture. Good luck with the clock, and let us know how well it keeps time over a longish period.:biggrin:

Will do, Honour, but there is a long way to go before I get to timekeeping! :yes:

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It's a nice job you've done there, many people turn them away, as we know there notoriously temperamental,  especially when the public get hold of them.

I've done  them before  now and a week or so later you get them back and the customer has turned the suspension wire has been turn into barley twist. 

I have one myself that I got from a car bootsale,  it had no suspension spring, but after looking through the 400 day bible I manage to make one up, strangely enough it's always gained, but after reading your piece I thought I'd  thin the wire down a bit and have another go at timing it in.

Keep us posted on yours. 

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18 minutes ago, antony said:

It's a nice job you've done there, many people turn them away, as we know there notoriously temperamental,  especially when the public get hold of them.

I've done  them before  now and a week or so later you get them back and the customer has turned the suspension wire has been turn into barley twist. 

I have one myself that I got from a car bootsale,  it had no suspension spring, but after looking through the 400 day bible I manage to make one up, strangely enough it's always gained, but after reading your piece I thought I'd  thin the wire down a bit and have another go at timing it in.

Keep us posted on yours. 

There are loads of online instructions for repairing, setting up, levelling, setting the beat, regulating, etc. Meadows and Passmore have an online suspension spring identifier which will tell you the correct one you need for your clock.

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  • 2 weeks later...

Now that I have the correct suspension spring and winding key, I can let down the mainspring carefully and dismantle the movement for cleaning in the ultrasound machine.

Anniversary clock

The bottom block on the suspension spring has a peg through it to connect to the pendulum and I made up a simple jig from a piece of scrap melamine faced board with a 1mm hole drilled in it to accept one side of the peg. This allows the block to sit flat on the board to facilitate the removal of the screws. It also allows me to stretch out the spring taut for marking.

Anniversary clock

The next pic shows the suspension spring being stretched out to mark the position of the verge fork and top block on a line extending away from the bottom block.

Anniversary clock

Anniversary clock

Now that I have my pattern, I can remove the old kinked spring and make up the new one using the marks as a guide. Here are all the parts laid out on the jig. The new spring is supplied over length...that's it beneath the old bent one at the top.

Anniversary clock

First, the spring is fitted centrally into the bottom block. (The bent one above is the old one).

Anniversary clock

Followed by the top block and finally the verge fork.

Anniversary clock

Anniversary clock

The holes in the front and rear plate were cleaned with peg wood to remove any old oil and muck, before reassembling the movement and oiling the pivots.

Anniversary clock

Anniversary clock

Now the base (newly polished and re-laquered) and columns are put back together, and the movement fitted to them.

Anniversary clock

Anniversary clock

Here you can see the verge fork sitting nice and centrally on the verge pin that moves the pallets, and thus the escape.

Anniversary clock

Now comes a long session setting the clock up. After levelling, the 'beat' has to be set up so that the clock ticks and tocks evenly, and the pendulum revolves an equal amount each way. Once that is acheived, then the clock will have to be regulated/timed by adjusting the balls on the pendulum in or out. Further together and they revolve faster, further apart, slower. It's a slow process, each adjustment needing several hours see the effect. More soon.

 

 

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The clock ran for a few minutes, then stopped. As the movement is running freely when the pallets are removed, it's obviously not a movement issue, more likely a transfer of power to the verge fork problem. The verge pin applies a tiny push to the verge fork everytime the clock ticks, and it's this that keeps the balls rotating. The height of the fork on the pin is critical....too high, and not enough pressure is applied, too low and too much is applied. I have to find the 'sweet spot'. I've lowered the fork on the suspension spring about 1mm, and the clock has now been running for a couple of hours with a lovely even rotation of the pendulum. Watch this space!

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3 hours ago, Roger the Dodger said:

The clock ran for a few minutes, then stopped. As the movement is running freely when the pallets are removed, it's obviously not a movement issue, more likely a transfer of power to the verge fork problem. The verge pin applies a tiny push to the verge fork everytime the clock ticks, and it's this that keeps the balls rotating. The height of the fork on the pin is critical....too high, and not enough pressure is applied, too low and too much is applied. I have to find the 'sweet spot'. I've lowered the fork on the suspension spring about 1mm, and the clock has now been running for a couple of hours with a lovely even rotation of the pendulum. Watch this space!

Interesting thread, I wish I had the patience for such a project! 

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@Always"watching" I know you were interested in the timing, so I came down this morning to find the clock still merrily ticking away, but it had lost an hour and a quarter since I set it going at about 4.00pm yesterday.

Anniversary clock

...and the actual time by the RC watch I set it to.

Anniversary clock

At the back of the clock, the regulating wheel can be seen. It's the knurled wheel on top of the pendulum. Turning it anticlockwise moves all the balls in toward the centre of the pendulum, speeding up the rotation, while clockwise has the opposite effect. So that I can see how much of an effect this adjustment makes, I have put a marker dot (easily removed later with a dab of acetone on a Q tip) at the front of the wheel to give me a reference point, then move it a quarter of a turn anticlockwise and restart the clock. In about 6 hours, I'll check the timing again and make another adjustment as required.

Anniversary clock

Here's the quarter turn anticlockwise.

Anniversary clock

Now I just set the clock to the watch and try again. I'll review this in 6 hours.

Anniversary clock

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18 minutes ago, andyclient said:

Just a point Roger but is the pendulum plumb centre ? Don't know if it is the camera angle but from the pics it looks off centre ?
Could it be fouling on the cup on the base , looks very close , almost touching in the 2nd pic.
Great work though , I had one ,but gave up on it , ***** thing :(

It looks off centre because I've turned it round to access the adjuster, Andy. When It's turned back, it will be centered as in the first pic. The mantlepiece has a slight front to back slope.

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