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Old 10th Aug 2011, 10:10 pm   #1
dennishoy
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Default Fibre wheel in old mains clocks.

Stupid question perhaps, but why is the first gear wheel off the rotor always made of fibre?

I have several old mains operated clocks which have sheared one or more teeth on the fibre gearwheel which is not surprising after 50+ years.

Now is there any reason why I can't manufacture new gear wheels from brass and get these old clocks working again?

The only electrical item is the insulated, wound coil over a laminated iron core which drives the rotor off the 50Hz supply.
The pinion of this rotor is meshed with a fibre wheel in all cases. Why fibre?
Is there a magnetic loop problem if I use brass?

Any thoughts?

Thanks.
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Old 10th Aug 2011, 10:39 pm   #2
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Default Re: Old mains clocks

The fibre wheel is simply for noise insulation. Synchronous clock motors produce a very weak buzz under load which, if the wheel was metallic instead of fibre, would by amplified through the train and plates and then the clock case. I therefore wouldn't advise making new wheels from brass.

The noise insulation, in turn, helps reduce wear on the (usually) brass wheels in the train.
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Old 10th Aug 2011, 10:53 pm   #3
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Default Re: Old mains clocks

Thanks Darren.

Looks like there is no simple repair then. Shame.
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Old 10th Aug 2011, 11:01 pm   #4
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Default Re: Old mains clocks

Mike Phelan, if he sees this, might be able to offer advice. For example, it might be feasible to cut new wheels out of Tufnol or Paxolin. If there is an answer, Mike will know it.

The only other answer is to salvage good wheels from scrap clocks, but that's very hit and miss and probably expensive in the long run.
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Old 11th Aug 2011, 9:45 am   #5
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Default Re: Old mains clocks

Darren's quite correct about the reason for using Paxolin wheels.

Cutting teeth in this material is really no different from cutting brass ones, except that as well as having a metal 'sandwich' disc to support the blank, you need brass discs on both sides of the Paxolin or Tufnol to support the latter.

Sharp cutter needed as well!

This wheel is the only one in the clock that has to be lubricated (with thin grease).
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Old 11th Aug 2011, 11:40 am   #6
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Default Re: Fibre wheel in old mains clocks.

Could a new wheel be cut from fibre material similar to the original?
If the original lasted for 50 years a new one might last another 50.

Apart the noise problem, I would advise against brass, any insulation failure of the motor could render the output shaft live, if this was connected via a brass gear wheel to the rest of the clock, then the whole mechanism could become live.
It seems probable that the basic insulation of the motor winding, and the insulated wheel between the motor and the rest of the mechanism, could be considered as double insulation.
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Old 11th Aug 2011, 5:00 pm   #7
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Default Re: Fibre wheel in old mains clocks.

Quote:
Originally Posted by broadgage View Post
Could a new wheel be cut from fibre material similar to the original?
Yes - see my post above.

There won't be an insulation issue with a metal wheel as the rotor is conductive with the movement frame.

The stator winding is a simple coil with a plastic former and likely failures are verdigris on the very fine wire and rotten insulated leads from it.
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Old 11th Aug 2011, 5:22 pm   #8
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Default Re: Fibre wheel in old mains clocks.

Is it possible to buy a suitable-sized nylon gearwheel, from RS or whoever? Although it may not be compatible with the shaft, it's a lot easier to turn-up a bush on a lathe than cut a gear wheel.
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Old 11th Aug 2011, 10:07 pm   #9
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Default Re: Fibre wheel in old mains clocks.

Thank you for all the suggestions. It's great to be able to 'discuss' things on here even though we are not in the same room.

This clock is an old 'sunburst' clock made by Orfac (says 'Made in Holland' on the dial. The case is made of brass and good quality. Likewise the movement, but the fibre wheel seems to be the weak point after many years. Perhaps the material reacts with the grease over a long period?

Well..... I've been giving some thought to ressurrecting this one as I do like it (it has a second hand too).

How does this idea sound as a temporary cure (bodge even) just to get it working until a more permanent solution can be found?

There are two teeth missing on the wheel. The meshing pinion from the motor is much wider than the fibre wheel it drives, so the fibre wheel could be a lot thicker.
I take a small piece of thin, flat brass sheet and clamp it to the good part of the gearwheel, I then file 4 new teeth into it using the existing fibre teeth as a template (with care!). I then rotate the filed brass to the damaged part of the gearwheel and line up teeth 1 and 4 with those of the fibre wheel and the missing teeth 2 and 3 should be in the right place. The new brass is 'Aradited' in place and allowed to dry.

If this fails, then all I lose is the fibre gearwheel which is damaged anyway.
I appreciate it would be only a 'bodge', but I'm not going to be looking at the movement as it's behind a plastic cover and a brass backplate.
I'm willing to try anything to get it working, but not at great expense as it was rescued for £2 at the local auction.

I'l post some pics once I've got it apart again.
It's not everyone's favourite, but it has sort of 'grown' on me over the last few weeks.
Can any of our friends from the Netherlands indicate how common are Orfac sunburst clocks, please?

Thanks.
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Old 11th Aug 2011, 11:18 pm   #10
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Default Re: Fibre wheel in old mains clocks.

Orfac (Original Fine Arts Collection) is a 1930s company, nowadays apparently operating more as distributors of other peoples products than anything else.

Their most familiar clocks are the Sallander type, common in the UK. Orfac Sunburst and Starburst clocks are quite rare, at least in the UK, but as you've indicated above a Netherlands member will probably know more.
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Old 12th Aug 2011, 9:16 am   #11
Mike Phelan
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Default Re: Fibre wheel in old mains clocks.

Hi Dennis
I'm not familiar with your clock either, but it certainly looks as if it's worth keeping.

Your idea about the wheel should work, albeit it might be noisy. At least the clock will be preserved.

Kalee, it would be a long shot if you could get a wheel with the right tooth count and diameter.
Not critical but there it's worth mentioning that the RS gears are involute tooth form, whereas clock wheels are cycloidal tooth form.
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Old 12th Aug 2011, 11:04 am   #12
60 oldjohn
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Default Re: Fibre wheel in old mains clocks.

Would the grafted piece of brass unbalance the cog causing vibration? Would it be better to graft a piece of fiber made with brass templates as Dennis was thinking? Just my two penny worth John.
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Old 12th Aug 2011, 12:10 pm   #13
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Default Re: Fibre wheel in old mains clocks.

No. Due to the gear ratio, the rotational speed of the fibre wheel is too slow to cause vibration through imbalance.
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Old 12th Aug 2011, 1:46 pm   #14
60 oldjohn
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Default Re: Fibre wheel in old mains clocks.

I'm wrong again, I thought that with the cog being on the motor shaft it would be rotating at a high speed. I stand corected. John.
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Old 12th Aug 2011, 2:48 pm   #15
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Default Re: Fibre wheel in old mains clocks.

It's not on the rotor spindle, John, but gears with it; typically with a ratio of about 8:1 so probably as slow as 150 rpm.

A picture would be good, Dennis.
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Old 12th Aug 2011, 3:06 pm   #16
60 oldjohn
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Default Re: Fibre wheel in old mains clocks.

Thanks Mike ,Shows what I know about clocks. John.
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Old 12th Aug 2011, 3:42 pm   #17
dennishoy
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Default Re: Fibre wheel in old mains clocks.

Thank you again everyone, especially Darren.

I've included some pictures here and I'm begining to think I would really like to see that second hand sweeping round in the near future. I've not seen it go yet!

Who thinks this clcok is ugly? I did at first, but I like it now.
This forum certainly makes one feel that an effort has to be made to get it going now.
Thank you all.
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Old 12th Aug 2011, 3:47 pm   #18
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Default Re: Fibre wheel in old mains clocks.

Could you fabricate a wheel using a flat piece of PET or HDPE plastic? I don't know what the wear characteristics would be though.
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Old 12th Aug 2011, 5:02 pm   #19
dennishoy
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Default Re: Fibre wheel in old mains clocks.

I think any hard wearing material would be fine. I don't have access to a gear cutting lathe so anything that makes it easier by hand would be good.

The wheel has a smaller brass pinion in addition to the fibre wheel so I would prefer to make something that attaches to the existing arrangement if possible.

I've been through several hundred gearwheels from old clocks and none have the correct diameter/number of teeth so I'm going to have to add something to the damaged wheel rather than replace it.
Like 'O' rings, there never seems to be one of the correct type no matter how many hundreds you search through.
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Old 12th Aug 2011, 5:14 pm   #20
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Default Re: Fibre wheel in old mains clocks.

There are a number of gear manufacturers who could probably manufacturer a gear from the correct or a more modern equivalent material, though at a price. My late father owned a gear factory and often made non metallic gears.

You could try Gibbs Gears http://www.gibbsgears.com/ I have never needed their services but my brother works for them.

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