Wobbly cabochons

[Fraser]

I have found recently that a few cabs I have bezel set have been wobbling after setting. I realise there could be various reasons for this, like the stone not being properly calibrated, the back plate being uneven, or the bezel being too loose or too tight (causing warping). I'm guessing the stones are slightly uneven as I got a job lot cheap from South Africa, and some do look slightly asymmetrical. It's annoying to only find out that it's wobbling after the stone is set, because then it must be removed and the problem rectified. I don't like using glue under cabs if possible, and anyway the bond can break during the pressure of setting. I have seen in some old rings I have taken apart that some cabs have a slither of material or card under them to cushion any wobble. Is this a good system, and if so what material should one use?

[mizgeorge]

It always used to be sawdust...

Most semi precious cabs can be very easily ground to flat with a bit of silicon carbide grit, a few drops of water and a flat piece of glass. Very quick and easy.

[Dennis]

Fraser,

If your stones are not completely round that should not make a lot of difference. More than likely you just don't have the bezel fitting well enough. Here are some useful aids:

Hold your bezel with its stone up to the light, or work on a light box (example below). It should fit closely and evenly, so that the stone can only just be inserted and lifted out with a cone of BluTack, or beeswax..

The bezel should be only just tall enough to hold the stone above its maximum girth when set.

As a beginner, you might cut your bezel strip from 0.4mm fine silver sheet, which is easy to rub over when annealed but stiffens in use.

If your bezel turns out a little too large, cut it through at the joint and re-solder. Each time you do this it will get a little smaller.

If your bezel is too small, stretch it a little on a small round mandrel, either by pulling it up with your fingers, or tapping it with a small hammer.

Packing, or a jump ring are sometimes used to make the stone taller, but an irregular base should not generally deter you . Dennis.

[SteveLAO]

The thin sliver of material was often used to enhance the colour of the stone rather than packing to ensure a tight fit. If you bought a job lot in SA, then they would probably have been "native cut", in other words cut to maximise the yield from the rough rather than to a calibrated size or a flat base! You've not mentioned what stones you are using, but most bases can be ground down flat without too much difficulty - just make sure there are not surface reaching fractures in the base or inclusions right up at the surface, both of which could be a concern if you're working on the stone!

[metalsmith]

Fraser,
work on a light box (example below). It should fit closely and evenly, so that the stone can only just be inserted and lifted out with a cone of BluTack, or beeswax. Dennis.

great lightbox there Dennis!

[Patstone]

Just what I was going to say, what a wonderful idea, I am always trying to hold stuff up to the light of the window and usually spend the next half hour crawling around the floor looking for the stone.

[mizgeorge]

Dennis posted a great thread about this a while ago, but I think the pictures may now be missing:

http://www.cooksongold.com/forum/showthread.php?t=1950&

[Dennis]

Hi, I did not stop to explain my pictures, but here are the reasons for the three components:

The LED cupboard light, from hardware shops, is easy on batteries and will probably go on for a year before you need to change them. However the surface is curved, so it helps to put it under some sort of flat lid, or into a box to give a working surface.

The white sticky tape is to reduce the glare of the light. I found two layers of tape works best. Once you can work on a back-lit surface tricky bezels are more easily dealt with too. Dennis.

[Patstone]

Talking about wobbly cabochons, I made a diochroic glass ring, it was quite a solid finish and about 1cm across. It has been on various craft tables and one woman in her seventies came up and tried it on, I was watching her and my daughter was serving someone else, the ring seemed to fit her, she could get it on without any pushing. When it came to decision time she said she didnt think it was suitable and then couldnt get it off, before I could offer her some vaseline she had wrenched it off, bending the bezel and of course the stone pinged out, then she left muttering that it couldnt have been very well made if the stone came out just like that. When I was able to get it home and look to see the damage, she had actually bent the silver at the back of the stone with the force of getting it off. Dont know if she did weight lifting as a hobby, but I would think she would be good at it. Anyway my question is, what thickness silver do you normally use for the back of a cabochon, I have been using 0.6mm is that too thin. This type of thing has never happened in the three years I have been making and selling.

[Dennis]

For the 10.0mm band, I would use 0.9-1.0 thickness metal. You could use thinner strip, say 0.8 and thicken the edges with wire. I presume the bezel was soldered straight onto the band.

When something like this happens, you can cast around for someone to blame, but the right thing is to learn the lesson and do better: myself included. Dennis.

[mizgeorge]

I've quite happily used 0.6mm backing plates for many pieces, including lots that are much larger than 10mm, but I would always strengthen with either a frame around the bezel or quite a thick bezel to try to ensure the plate won't warp if it's handled roughly. It can be a useful way of keeping the weight of a piece below 7.78g if there isn't going to be time to get them hallmarked.

On a related note, it's far easier to remove a stuck ring by 'pulling' the skin through from the bottom of the finger in gentle stages, rather than trying to use a lubricant. It also avoids having to repolish the ring (if it's still in one piece!)

[Patstone]

Well to start with she had grasped it and pulled it crooked before I realised that she was taking it off, or trying to. I always make bezels bases out of sterling silver, thickness normally varies according to the size of stone. On this occasion I made the wall of the bezel from 0.4mm sterling to give it a bit more umph to stop it getting bent so easily, then the whole stone holder was soldered onto the ring

4971

This was work in progress before all the "dings" were taken out.

[Dennis]

It's a lovely looking ring and I realise now it was the cab that is 10mm across, not the shank. Even so, if she had bought it and destroyed it at home by taking it off, I think she would still have reason to complain.

So I think there's still a case for reinforcing the design and giving it a test drive for a few weeks to see how it survives normal wear and tear. Dennis.

[Patstone]

I made one similar to keep for myself because my daughter bought me the glass (I normally use semi precious, but this one caught my eye), different colours, but the design and size is the same and it was made at the same time, and although I only wear it occasionally it has stood the test of time, so I am still convinced it was brute force and ignorance on her part. The only thing I can say in her defence was that it was hot, so she may have panicked a bit when she found it was stuck.


It's a lovely looking ring and I realise now it was the cab that is 10mm across, not the shank. Even so, if she had bought it and destroyed it at home by taking it off, I think she would still have reason to complain.

So I think there's still a case for reinforcing the design and giving it a test drive for a few weeks to see how it survives normal wear and tear. Dennis.