Suspension spring bottom block too thick

[DenisG]

Hello all,

I have what is hopefully a fairly simple question for those of you adept at metal working (which I am admittedly not). I am repairing the movement of an English long case clock. The clock had suffered some damage and one of the casualties was the suspension spring, in fact the owner unscrewed it from the top of the pendulum rod and threw it away. I have procured a replacement from a supply shop which I believe will do the trick with one problem. The lower block is too wide to fit through the crutch. I would estimate that it needs to be around 1/8" thinner.

Wow, that was long winded. Does anyone have a good method to 'shave' 1/8" from the bottom block which will leave it looking like it hasn't been butchered?

Thanks!

Denis

 

[DenisG]

Hello all,

I have what is hopefully a fairly simple question for those of you adept at metal working (which I am admittedly not). I am repairing the movement of an English long case clock. The clock had suffered some damage and one of the casualties was the suspension spring, in fact the owner unscrewed it from the top of the pendulum rod and threw it away. I have procured a replacement from a supply shop which I believe will do the trick with one problem. The lower block is too wide to fit through the crutch. I would estimate that it needs to be around 1/8" thinner.

Wow, that was long winded. Does anyone have a good method to 'shave' 1/8" from the bottom block which will leave it looking like it hasn't been butchered?

Thanks!

Denis

 

[stewart]

Hello Denis

Use a German milling machine.

Stewart

 

[DenisG]

Hi Stewart,

Unfortunately, I don't have one... actually I don't even know what it is!

Denis

 

[stewart]

Hello Denis

A file. You can do any thing with them, especially good sharp ones of the proper cut.

Stewart

 

[LaBounty]

Hey Denis-

As Stewart says, you can use a file. But for this kind of job, instead of working the file over the suspension block try working the block over the file. I've found this will keep the piece flat where as keeping it flat is more difficult when working the file over the piece. And keeping the suspension block flat, with both sides parallel, is important so you don't end up with severe pendulum wobble.

I've also used this method with buff sticks but another suggestion would be to put sandpaper on a thick piece of glass and work the block on that.

And you are absolutely correct to change the thickness of the suspension block rather than trying to make the crutch wider.

Good luck with it!

 

[DenisG]

Thank you Stewart and David, I will set about filing the block down today. Appreciate the advice as always.

Denis

 

[Mike Phelan]

Denis
A couple of things.
File both sides so the pendulum rod and spring are symmetrical.
Use new files on brass, then those that have worn, use for steel.
Don't worry, you do not have to install a machine shop to file a lump of brass! Occam's Razor

 

[DenisG]

Thanks Mike! Appreciate the guidance. I always like to hear from you. Reminds me of home - I'm originally from Dumfries in Scotland. Also, I would appreciate your comments on another English long case I'm working on, this one with switchable chimes. Either westminster on 4 coiled gongs mounted in the case (plus 1 for the strike), or Whittington (oops... St. Michael) on 8 nest bells. I'll post a new thread in the Clocks forum.

Thanks,

Denis

 

[Mike Phelan]

Originally posted by DenisG:
Thanks Mike! Appreciate the guidance. I always like to hear from you. Reminds me of home - I'm originally from Dumfries in Scotland. Also, I would appreciate your comments on another English long case I'm working on, this one with switchable chimes. Either westminster on 4 coiled gongs mounted in the case (plus 1 for the strike), or Whittington (oops... St. Michael) on 8 nest bells. I'll post a new thread in the Clocks forum.

Thanks,

Denis

You're welcome, Denis. Your LC sounds a bit like the one that Joe G has, but a bit later.

 

[Pete Riegel]

AVOIDING PENDULUM TWIST

While I was putting together the pieces for a newly-acquired grandfather clock I noticed that the rectangular block at the bottom of the suspension spring had been filed in such a way as to leave a high spot in the middle, at both sides. I believe this was done to reduce the possibility of pendulum twist.

Ideally the crutch will contact the pendulum rod in such a way that it does not tend to impart a twisting motion to the rod. The is not a problem when the rod is round, as the crutch will hit the rod on center.

However, when a crutch with a rectangular hole hits a rectangular suspension spring block, the alignment between hole and block must be absolutely perfect, or else the impact will hit the block on opposite corners, imparting a twisting force to the rod. Perfect is something we never achieve. Close, yes. Good enough, often. Perfect, never.

By tapering the block, the impact point is moved to the center, eliminating the twisting component of the contact force.

View attachment 389

 

[LaBounty]

Hey Pete-

Interesting observation! Maybe that's why American manufacturers went with a round feather instead of a brass block.

But, I hope you aren't suggesting that everyone bevel their suspension blocks to fix their pendulum wobble . That's sounds like a procedure that isn't easily undone. I believe the proper fix for pendulum wobble in this case is to tighten the crutch so it fits the block (or shim the block so it fits the crutch). Then, if you add a bit of grease where they meet, it isn't necessary to be perfect.

And I would look for the reason why the block and crutch aren't parallel. Your picture shows a block twisted in the crutch. That would imply either the crutch foot is bent at an angle, or the suspension stud has a problem, or the suspension spring is twisted, or...

Please don't think I'm being critical but I'm not sure beveling will make much difference and may actually increase wobble.

I may have to go experiment now .

 

[Pete Riegel]

I'm certainly not suggesting that anybody do anything. If there is no problem, why fix it? However, if one has pendulum twist, the crutch/block geometry is a place to look for a fix.

Getting the slot in the crutch to be nice and parallel with both sides of the block can be quite time-consuming, as it involves a lot of crutch-twisting and close examination. Also, if the slot in the crutch, and/or the two sides of the block, do not both have parallel sides, it will be impossible to get uniform contact on both sides of the swing.

The high spot in the middle guarantees a central strike by the crutch to the block. If I had fiddled with a new suspension spring, and its supporting bracket, and the pendulum still wobbled, I'd think seriously about filing the block.

With a brand-new block that's too thick I think I'd file it to get a high spot in the middle. After all, I have to file it anyway, and it's a tough job, using a file, to get both sides absolutely parallel.

 

[david bishop]

interesting observations Pete. I like the idea of a round pendulum block, and I'm wondering now why the old timers used the square or rectangular ones in the first place. For reasons that you have stated, round blocks appear to be a more practical application. Maybe some of the more "scientifically informed" readers will disagree, but when next I have to make up my own suspension spring and block unit for an old longcase or similar, I am seriously considering making a round, and not flat, block!

David

 

[Mike Phelan]

Originally posted by david bishop:
I have to make up my own suspension spring and block unit for an old longcase or similar, I am seriously considering making a round, and not flat, block!

David

JMO, but if something has worked for a century or three, I would be inclined to leave it so. There is an issue of changing, albeit minor, the design of an antique.

 

[david bishop]

PS to my last post.

The French were very good clockmakers, and I have only ever seen French clocks with round pendulum rods which fit between the crutch.

David

 

[Pete Riegel]

Ever wonder why the suspension springs on grandfathers are so long? I have. Seems to me that the extra spring length serves no useful purpose, as all the bending occurs within a fraction of an inch of the top.

Could be an easier way to get center contact would be to use a shorter spring and raise the block clear of the slot in the crutch, and let the crutch hit the rod directly.

Of course, this may be difficult if the steel rods currently on sale aren't long enough. I haven't looked at this.

Also, this violates the sanctity of adherence to the original configuration, which bothers some folks more than others.

 

[Joe Collins]

OK, I am thoroughly confused. I always thought the crutch acted on the pendulum rod or pendulum leader NOT on the suspension spring block. If this is the case filing the spring block in a diamond shape will have no effect on how the leader reacts to the crutch.With a round rod or leader there would be no twisting motion transmitted.

JMO

Joe

 

[DenisG]

This has turned into a very intersting discussion which I have been following closely. In the meantime, just to close on my original question, I have filed the block down to size working the material over the file as David suggested. Perfect fit, and the clock is up and running.

Joe, the discussion on 'shaping' the bottom block is in relation to English tall case clocks where the crutch does indeed act directly on the bottom suspension spring block. The pendulum rod is usually screwed directly into the block.

Denis

 

[Mike Phelan]

Originally posted by Joe Collins:
OK, I am thoroughly confused. I always thought the crutch acted on the pendulum rod or pendulum leader NOT on the suspension spring block. If this is the case filing the spring block in a diamond shape will have no effect on how the leader reacts to the crutch.With a round rod or leader there would be no twisting motion transmitted.

JMO

Joe

Joe
No need for confusion.
That depends entirely what sort of clock we are talking about.

Generally, French, some German and American clocks do, as you say, have a round rod that embraces the crutch loop or fork; English dials and some German clocks use a slot in the pendulum rod and a pin in the crutch.

English (and probably American?) longcases have a long suspension spring whose lower block embraces the crutch fork; the round pendulum rod is screwed to the block below it.
This make sense?
HTH

 

[Joe Collins]

Denis and Mike,
Thanks very much for ending my confusion. I guess I have much to learn but I'm getting there.

Joe

 

[shutterbug]

I would have just ordered the correct suspension spring, but your way sounds like more fun, and it worked so what can I say? :0)

 

[Pete Riegel]

Always fun to take a view from a different perch:

A rectangular block inside a rectangular hole, properly set up, braces the suspension spring against twisting. This keeps the pendulum from wobbling.

 

[DenisG]

Hi Shutterbug,

I too would have ordered a correctly fitting suspension spring, had one been available! Trust me, I don't have the time to cause myself additional work on purpose

Denis