Making a brass pendulum bob for a verge clock

NigelW

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Jan 2, 2015
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I need to make a bob pendulum for a verge bracket clock. I believe these were made of solid brass, unlike longcase pendulums which are generally brass shells filled with lead.

The bob needs to be adjustable by sliding up and down the squared end of the pendulum rod and held in place with a screw through the centre of the disc. If the bob is turned or cast in one piece how does one square the hole? Should it be made in two halves and soldered together? Could one made a model with a square hole and cast that?

Any suggestions would be appreciated.
 

Uhralt

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Sep 4, 2008
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I need to make a bob pendulum for a verge bracket clock. I believe these were made of solid brass, unlike longcase pendulums which are generally brass shells filled with lead.

The bob needs to be adjustable by sliding up and down the squared end of the pendulum rod and held in place with a screw through the centre of the disc. If the bob is turned or cast in one piece how does one square the hole? Should it be made in two halves and soldered together? Could one made a model with a square hole and cast that?

Any suggestions would be appreciated.
I don't know how the originals were made. If I knew I would try to mimic that process. Regardless, you could drill an undersized hole and use square needle files to square the hole. Or you could use a square reamer that is pushed down the round hole. This is similar to how the square holes in winding keys are made.

Uhralt
 

NigelW

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Uhralt

Thank you so much for your reply. Square reamers are things I had never heard of before! I have made square holes in relatively thin material by filing, but a hole through the diameter of a pendulum is very long in relation to its width and filing. I have now found this video which is most interesting:

Nigel
 

NigelW

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My thinking on how to do this. The mandrel wouldn't necessarily need to be shaped exactly to the curve of the bob - some packing might do the trick. The important thing will be to stop it rotating, and getting damaged.

Making pendulum.jpg
 

Uhralt

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Uhralt

Thank you so much for your reply. Square reamers are things I had never heard of before! I have made square holes in relatively thin material by filing, but a hole through the diameter of a pendulum is very long in relation to its width and filing. I have now found this video which is most interesting:

Nigel
That's what I was talking about!
 

Uhralt

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My thinking on how to do this. The mandrel wouldn't necessarily need to be shaped exactly to the curve of the bob - some packing might do the trick. The important thing will be to stop it rotating, and getting damaged.

View attachment 554329
This looks like a plan! I like the idea to start with something square. That will make holding the part for proper broaching much easier.

Uhralt
 

kinsler33

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I'd just drill a round hole through the pendulum to fit the square pendulum rod. Then drill and tap another hole perpendicular to and intersecting the first. A screw threaded down this second hole will keep the bob from rotating on the shaft. Use a bit of LocTite or whatever to maintain the position of the second screw.

I can't do an illustration right now.

M Kinsler
 

NigelW

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I'd just drill a round hole through the pendulum to fit the square pendulum rod. Then drill and tap another hole perpendicular to and intersecting the first. A screw threaded down this second hole will keep the bob from rotating on the shaft. Use a bit of LocTite or whatever to maintain the position of the second screw.

I can't do an illustration right now.

M Kinsler
Thank you. Your idea is completely sound, but my research into clocks of the age mine indicates that the bobs had square holes and I am trying to reproduce as far as I can can the style of the original.
 

D.th.munroe

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I know when casting lead ones we used a dummy rod made from aluminium, a brass one coated in graphite I'm told works as well, I was thinkin a graphite dummy rod might work in solid brass casting.
 

DeanT

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I've got a couple of later ones which are lead filled and made in 2 parts.

Although the earlier ones appear to be solid brass. They are actually quite fine.

No idea how they are made....
 

novicetimekeeper

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I know when casting lead ones we used a dummy rod made from aluminium, a brass one coated in graphite I'm told works as well, I was thinkin a graphite dummy rod might work in solid brass casting.
They were remarkably good at casting, they may well have cast with an insert in the mould though I'm not sure they had access to graphite in that form. They had plaster of paris. When you look at their sheet casting techniques it is simply remarkable.
 

kinsler33

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Could you square-up a round hole by using a jeweler's saw? Seems to me that I might have done that once. Probably some sort of alignment jig would be a good idea, though I do like the idea of the square hole broach.

The gasket surfaces of the cast-iron cylinder head castings of the Ford 302 V-8's were machined in a single swoop with a monster broach. The teeth were bolted in individually. I saw this when I worked at Ford's Cleveland Engine Plant #1 in Brook Park, Ohio in 1967 or so, and I never lost my fascination with the place.

Mark Kinsler
 

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