Pivot Sizes

[Scouseget]

I've been having lots of fun, and a good deal of frustration, working with a couple of English fusee pocket watches from around 1875. Surprisingly, I've been able to semi-master the intricacies of the fusee cone (dismantled, cleaned, lubricated, and reassembled) and chain (which was broken but I was able to repair it with the tiniest of rivets
), but am being presently stymied by a broken English lever arbor pivot on one of them. One end is not only broken but also missing so I can't establish the diameter, so my question is, are the pivots usually the same diameter on both ends of any arbor? This can be for a balance, lever, or indeed any other wheel arbor? Can we make that assumption, and if not, how do you make a replacement arbor, which is next on my work list for this watch, if you don't know what diameter to make it? 

I do realize that I can simply try the remaining arbor in both jewel holes and try to establish the size that way, but it's a bit inexact and frankly I don't know how much clearance is normal, i.e., if a jewel hole is, say, 0.15mm, what size should the corresponding pivot size actually be?

I see that occasionally jewel gauges come on sale on E Bay, but these appear to be rare beasts at the best of times, and are usually prohibitively expensive so is there another method of measuring a jewel hole size? 

Finally, why wouldn't the pivots be the same size on an arbor? Presumably the loading on each of the pivots would be the same so logic dictates that the sizes could also be the same, or am I missing something and making too many assumptions?

As always, thanks in advance for any light you can shed on this.

The first photo shows the broken arbor. The second is the fusee opened up. Amazing precision given the technology of the day I think.

[oldhippy]

For starters, you need the right tools to begin with. A good lathe and milling. The arbor is made out of a single piece of steel. You need to measure both holes in the plates and barrel, then you need to be able to draw up plans and design the arbor, taking a look at others will help.   

[szbalogh]

Or You dont need to bother with measuring just try the hole on the arbor on the lathe. 

[jdm]

On 9/6/2017 at 3:31 AM, Scouseget said:

I see that occasionally jewel gauges come on sale on E Bay, but these appear to be rare beasts at the best of times, and are usually prohibitively expensive so is there another method of measuring a jewel hole size? 

Do you have a lathe?
You can then turn a series of trial pivots of a known size, pressed into a small brass handle.

[oldhippy]

I wouldn’t think this type is expensive.  

[jdm]

17 minutes ago, oldhippy said:

I wouldn’t think this type is expensive.  

That is for measuring pivots, the OP was asking was asking about jewel holes.

[oldhippy]

5 minutes ago, jdm said:

That is for measuring pivots, the OP was asking was asking about jewel holes.

My mistake. I had a senior moment.

[oldhippy]

This one does both. I wouldn't think it costs to much.

 

The problem you have the tools are precision. Cheap imitations won’t be so good.  

[Tmuir]

1 hour ago, oldhippy said:

I wouldn’t think this type is expensive.  

 

Depends on your idea of expensive.

Second hand anything from £50 to £120.

Its on my want list, but so are many other items

[jdm]

3 minutes ago, Tmuir said:

Depends on your idea of expensive. Second hand anything from £50 to £120.

Definitely expensive for something that can also be measured with a micrometer.

[oldhippy]

How are you going to measure the inside of a jewel hole with a micrometer?

[Tmuir]

I think he was referring to my post which was about the pivot gauge for pivots, not your post about the hole.

On clocks you can measure the pivot hole with a smoothing broach and then a vernier or micrometer on the broach, I've never tried to measure the pivot hole on a watch, but can you do the same if you have fine enough smoothing broaches?

[oldhippy]

Never used that way before. I suppose you can but you will still need to make small alterations to the pivots.  I had a set of very old markers tapered and a chart to match., again you sometimes needed a lathe to be able to alter.