Pivot polishing question

Cespain

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I have been using my small lathe to burnish/polish the pivots on an old mantle clock that I am working on. I mount the wheel in an appropriate sized collet in the headstock and then use a burnisher to do the work. This approach works very well until I come upon a wheel which due to the short length of the opposite end of the arbor cannot be mounted in a collet, as in the wheels pictured below. So I am looking for some advice on how best to polish these. Is there some other way of mounting them in the lathe or do I need to resort to a manual approach. Many thanks for any suggestions.

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John P

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We use a collet that fits the pivot to first of all check for a bent pivot. We find bent pivots quite often.
I have a tool that supports the opposite pivot which allows me to burnish that pivot safely. It is placed in the tailstock and is made of brass with a hole drilled in the end and half of that removed to form a channel for the pivot to lay in. This supports the wheel when burnishing.
I dont have a picture of it but others may come along that do. It is a common tool used by clock repairmen.

johnp
 

KurtinSA

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For the type of wheel on the left, I have collets that would fit over the pinions to hold the wheel/arbor in place. For the situation on the right, I would find a collet that fits the large end at the bottom in the picture. Then I would support the arbor with a safety rest (I think that's the name). Also a 3- or 4-jaw chuck or bezel chuck can come in handy to hold the wheel along with the safety rest.

Kurt
 

wow

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Butterworths sells three grades of pivot polishing disks that are held in a small mandrel and mounted in the lathe. You hold the pivot in hand and polish it on the spinning disk. Perfect for such pivots!
 

Brunod

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I work this way on small parts.
It's possible to do the same with bigger parts.
IMG_0329.JPG
IMG_0273.JPG
 
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Cespain

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Thanks for all the tips guys. I have a good selection of collets that I got with the lathe (an old Pultra 10 made in England) but some are missing and none that would be big enough to accommodate the pinion. I'm not sure if this lathe takes 'standard' WW collets - I will investigate. I will also look for a steady rest which could resolve a few of the issues though again the Pultra is not that common a lathe and accessories are difficult to find and expensive!

Butterworths sells three grades of pivot polishing disks that are held in a small mandrel and mounted in the lathe.
I had looked at these some time ago but not followed up on it, perhaps now is the time.
 

Cespain

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We use a collet that fits the pivot to first of all check for a bent pivot. We find bent pivots quite often.
Do you rely on a visual examination of the pivot to determine whether or not it is bent or is there some more technical way to do it? I sometimes wonder if what appears to be a slight bend is an optical aberration caused by the magnification of my loupe. I would also be interested to know how you straightens such pivots, without breaking them of course. I have had mixed results in this regard using parallel nosed pliers or a small piece of tubular brass fitted over the pivot and levered at the opposite end.
 

Brunod

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Concerning watches, there is a tool to straighten bend pivots.
There are also special sturdy tweezers there for.
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Edit : Here I have found the tweezers pict on the web
1656232173085.png
 
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gmorse

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Hi Brunod,
Concerning watches, there is a tool to straighten bend pivots.
This, extremely expensive, (over £530 in the UK), Bergeon Seitz tool is known by many under another name, the 'pivot breaker'.

To check if a pivot is bent, I set it up in the lathe in an appropriate sized collet and spin it, which quickly shows whether there's any runout at the other end. It's then an easy matter to ease it back straight whilst slowly rotating it. Jerry Kieffer uses a small mounted ball race in the tool holder to do this with greater safety. This clearly won't work if the pivot is very badly bent, which usually means a re-pivoting job.

Regards,

Graham
 

gmorse

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Hi cespain,

The whole subject of burnishing versus polishing of pivots has been widely covered in various threads in the past, and it seems that confusion continues. There is a difference, and I'll leave you to do your own searches. However, in essence, polishing and burnishing both remove material from the pivot, but burnishing also moves the metal surface and consolidates it. To do this effectively, some significant pressure must be applied to the pivot by the burnisher, which demands that the pivot should be securely and directly supported to resist it, otherwise breakage is a real risk. This is the purpose of the Jacot tool and drum which Brunod shows in his post #6. Pivot breakage is clearly less of a risk as the size increases, but the principle of directly supporting the pivot being burnished is a sound one.

Regards,

Graham
 

Cespain

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I have made a few different size pivot supports from brass tubes of appropriate internal diameters which I cut in roughly half horizontally and mount in the tailstock. ( I think I read an entry about this in an earlier post in this forum.) The pivot rests in the hollowed out tube with sufficient proud of the tube to apply the burnisher. The only slight drawback to this is that you have to burnish from the top of the pivot which I find makes it more difficult to see exactly what you are doing as opposed to burnishing from the bottom.
 

Brunod

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Hi Brunod,
This, extremely expensive, (over £530 in the UK), Bergeon Seitz tool is known by many under another name, the 'pivot breaker'.
...
Graham
Hi Graham,
Nice name, indeed, pivot breaker. But it's usually what happens half of the time when trying to straighten a bend pivot anyway. And if it is successful, it's sometimes because it's a marshmallow pivot, much too soft to do the job.
The high price you mention is certainly for a new one, but taking time and exploring second hands tools may be rewarding.
As new, I could nearly afford none of real tools...


IMG_1409.JPG
 
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Jerry Kieffer

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I have been using my small lathe to burnish/polish the pivots on an old mantle clock that I am working on. I mount the wheel in an appropriate sized collet in the headstock and then use a burnisher to do the work. This approach works very well until I come upon a wheel which due to the short length of the opposite end of the arbor cannot be mounted in a collet, as in the wheels pictured below. So I am looking for some advice on how best to polish these. Is there some other way of mounting them in the lathe or do I need to resort to a manual approach. Many thanks for any suggestions.

View attachment 714279
The first attached photo shows a Lathe tailstock support as mentioned by John in post #2. This arrangement supports the pivot for the use of a burnisher where greater pressure is applied.

However, as Graham has mentioned in post #11, metal is often removed to some degree using the burnishing and polishing procedures. To prevent the possible taper effects of hand holding tools, I use a ball bearing tool post support as shown in photos #1 and # 2. This assures that the pivot surfaces will remain parallel or will be returned to parallel.

When polishing pivots, the pivot needs to be excess-able to perform the procedure and often requires a study rest as shown by Jonas in post #5.
Again however, I have found that steady rests can score or mark polished surfaces depending on proper alignment, pressure required and lubrication. To resolve this I have mounted ball bearings in all of my steady rest arms per third photo.

Jerry Kieffer
43B38579-35A8-4A0E-B023-CDCFEB14D81B_1_201_a.jpeg 51907D59-B8BC-48C1-BD96-058A1A52BAE4_1_201_a.jpeg View attachment 714445
 

Dells

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I think you will find the Pultra 10 has a different thread to the American WW lathe this may help , plus there are quite often Pultra 10 8mm collets on eBay.
B33A847D-ADEC-48B6-BD5C-07047B1F939C.jpeg [/QUOTE][/QUOTE]
 
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Cespain

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Thanks Dells, I'll keep a look out for them but unfortunately when you add postage to Ireland they can turn out to be quite expensive.

As regards a steady rest, I did see one some time ago on lathes.co.uk but didn't commit to buying it at the time (when the Uk was still in the EU and there would be no import/customs charge) as I was only starting and didn't see the need for it then. I'm not sure I have the skill or equipment to make a proper one but some of the other ideas for supporting the arbors while polishing are certainly a good starting point and I'll certainly try them.
 

Dells

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Hi Cespain
I made this ( see picture) to polish pivots, it fits in my tailstock and is relatively easy to make, the worst bit is drilling some sub 1mm holes before turning the O/D of the brass down to reveal 1/2 the holes.
Dell
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