Advice needed in regards to a Porcelain Dial

[saswatch88]

Ok i need some advice on how to safely remove this sub-dial off of this porcelain pocket watch dial. I know its solder but i can use an iron to remove it because the heat can cause the porcelain to crack which seems to have happened already because this was an attempted repair. The sub dial looks off because it must have broke and someone tried to re-solder it but did it crooked. So i need suggestions on how to attack this I have a replacement and i plan to glue it on. The dial is very rare and worth about $500 so i dont want to mess it up. I cleaned the dial already so the hairlines are virtually invisible. Iam asking because i cant find any info on the net. Thanks

Edited January 21, 2020 by saswatch88

[Chopin]

What material is that ? Could an electric circuit soldering gun melt it ?

I'm saying this as I believe the key point here is temperature...

[AndyHull]

I suspect they the key to this is even gentle heating. The reason that ceramics tend to crack is generally because there are heat gradients across them, and a temperature differential between the substrate (generally copper or copper alloy). This induces stress cracks, when the substrate or the surrounding part of the object ( the dial in this case) does not expand as quickly as the area being heated. 

If the dial is gently heated on a hot plate, or with hot air, and allowed to come up to a uniform temperature, then there should be less tendency to crack. Similarly once you have done the repair, the object should be allowed to return to room temperature gently, with no cold drafts,  otherwise thermal shock will cause cracking.

Could you use an electric soldering iron. Perhaps, but it would need to have a high thermal mass (i.e. you need a big bit). Also it would tend  to produce a lot of very local heat, so it may cause cracking.

A hot air gun, of the sort used for  electronic surface mount rework, might be more appropriate, assuming it can reach the required temperature.

These can heat the whole work piece if used correctly. They are relatively inexpensive from the usual dubious sources in China, or you could try your local DIY shops. The critical parameter is how hot the thing can get, and can you control the temperature to with a few degrees, and keep it at an even temperature while you work.

If you look on line at people working with glass (and enameled dials are basically glass on a metal substrate), you will see that the process invariably involves gentle heating to bring the work piece up to the working temperature. Generally they work with gas torches, but these require a fair bit of skill to use without cooking the work piece. Slightly off topic,  I have seen someone doing surface mount circuit board rework repair with a gas torch and a plumbers electric iron, many years ago in a backstreet repair shop in Senegal. It can be done, but there are better and safer ways to do it. 

If the solder is leaded, then it will have a relatively low melting point, but this doesn't mean you wont need to gently preheat.  If it is silver solder, then you may need much more heat. Others with more knowledge would know which type of solder is more likely. Adding leaded solder to silver can lead to some pretty grubby results, so it would be as well to find out what you are dealing with before you jump in with both feet.

I would suggest picking up some scrap dials from ebay and practicing with those. They are cheap as chips if you hunt around the job lots.

I have a supplementary question. How did the creators of these dials manage to produce such fine detail? Is (or more correctly, was) this some form of screen printing process?

Edited January 21, 2020 by AndyHull

[AndyHull]

39 minutes ago, AndyHull said:

How did the creators of these dials manage to produce such fine detail? Is (or more correctly, was) this some form of screen printing process?

I've just answered my own question.

These dials are also pad printed, but in this case, obviously with enamel.

Furthermore, the elements are soldered together with tin (not lead) solder, using a very large soldering iron, however to repair them, you may well need to heat the entire dial as I described, in order to avoid stress cracks.

Edited January 21, 2020 by AndyHull

[saswatch88]

29 minutes ago, AndyHull said:

These dials are also pad printed, but in this case, obviously with enamel.

Furthermore, the elements are soldered together with tin (not lead) solder, using a very large soldering iron, however to repair them, you may well need to heat the entire dial as I described, in order to avoid stress cracks.

Great video, i know the paint is fired into the enamel which is great because it makes it safe to clean in an ultrasonic. I have tons of spare dials some are already cracked and unusable so i will practice with those first, i do have a heat gun with temperature variations so i will try that first, interestingly i had one dial i was cleaning in an ultrasonic and it actually made the solder come loose and the subdial came out, unfortunately this did not occur with this dial, i was considering using diamond burrs to grind of enough to release it but that is risky too, i just want to save this dial because it has tremendous value, I have seen they sell for close to $500 just by themselves. It’s a Waltham bold Arabic red 12 dial, i have only seen 4 pop up in the last 3-4 years and the lowest i seen one sell for was $267 with cracks and a chip. People will buy them and then pay 2-300 to get them restored. Which is what i was going to do but after  putting the dial in an ultrasonic submerged in Polident denture cleaning solution, the results were astonishing so all i need now is to fix the subdial and i have a really nice dial.

[AndyHull]

One more thing... flux.

If you are soft soldering, use a quality solder, tin based, and flux. It sounds like most of the modern "lead free" solders for electronic work would be ideal.

The dial picture above looks like it was soldered in a frying pan, and the reason it isn't bright and shiny, as well soldered joints should be, is because whoever did that job didn't use appropriate flux.

Get a few of these. https://www.ebay.co.uk/itm/1PCS-YOSKER-951-Rosin-Flux-Pen-DIY-PV-Solar-Cell-Panels-for-Electrical-Soldering/113759766800?hash=item1a7c9c4910:g:nAMAAOSwI3RW96Vz

They are inexpensive, and make a big difference.

Use the flux both for removal and for re-fitting. You can't use too much flux.. use plenty, it will boil off while it is doing its work, and any that remains can easily be cleaned off after.

Don't be tempted to use plumbers flux, as it is generally acid based, and will etch away the substrate if not cleaned properly. It also generally requires a higher temperature to activate than most soft soldering fluxes, which is fine if you are banging together a few lengths of water pipe, but not the best if the item is delicate.  Also once soldered, always clean off any excess flux, even if it claims to be "no clean" flux. Use ispropanol or denatured alcohol for this.

Edited January 21, 2020 by AndyHull

[AndyHull]

57 minutes ago, saswatch88 said:

putting the dial in an ultrasonic submerged in Polident denture cleaning solution,

Tip duly noted. Thanks.

[AndyHull]

One more trick. You might like to try using Kapton tape to hold the subdial in position from the dial side. This polyamide tape is safe for soft soldering temperatures, and shouldn't leave any residue when removed.

This would allow you to position and re-position very carefully from the dial side until it is perfect,  prior to flipping over and soldering from the back. Most of the generic polyamide tape you find on ebay will claim to be "Kapton" tape, but despite being a generic copy is should work just fine.

If using the generic stuff, obviously test the claim that it is actually heat safe, on a test dial prior to use on anything that matters.

Edited January 21, 2020 by AndyHull

[AndyHull]

8 hours ago, saswatch88 said:

I have a replacement and i plan to glue it on

If de-soldering  the old one doesn't cause issues, I would solder on the new one. Glues on metal will fail in time. 

The process I would use is as follows.

1) Carefully clean the metal surfaces which are going to be soldered. They need to be good clean shiny metal. Enamel obviously wont solder, so you need to be able to see the underlying substrate, and it needs to be as clean and as oxide free as possible. 000 gauge steel or copper wool, or fine grit emery paper will get you a good clean surface.

4) Carefully position the dial, using Kapton tape, per my previous post.

3) Clean off any grease, fingerprints etc with denature alcohol or acetone, any impurities will tend to boil, or caramelise, resulting in a poor finish, or a dry joint, so make sure things are well cleaned.

4) Apply flux generously to the area being soldered, it doesn't matter if any gets on the dial side, it can be cleaned off afterwards, what matters is that the finished joint is a bright clean joint and that the solder 'wets' the surfaces well. Dry joints fail and look ugly, this is what has happened to the original joint.

5) Gently warm the dial up to something close to the solder's melting point if you can, perhaps 100C would be close enough with hot air or a small heat plate. Add more flux if needs be, but not when things are too hot, as you don't want to shock the work piece.

6) Now solder the joint. Apply sufficient heat, and the solder at the same time, work quickly. The solder should flow quickly, and look bright and shiny as it flows. Electonic "flux cored" solder will work best. Using tin strip would work too, but why make life complicated for yourself. Avoid plumbers solder, it may have an acid flux core. The additional flux in the flux cored solder will also allow it to flow much more readily, and cleanly.

Use just enough heat to allow the solder to flow. Too little and the joint will be brittle, too much and you risk damaging the dial. This is where practicing on the scrap dials will pay off.

The soldering iron in the above video has a very generous head, this will help as the extra thermal mass will allow quick even heat transfer to a relatively broad spot. Using a fine tipped iron may be counterproductive as it may cause much more local heating, risking poor solder flow, and heat stress cracking of the enamel.

7) Allow to cool gently, do not be tempted to blow on the thing, or cool with water.

8) Don't forget to show us the results.

 

Edited January 21, 2020 by AndyHull

[Chopin]

Can you show us the front ? I'm curious how it looked originally and what your results were after working on it. It's always nice and educatioal to see succesful restorations.

If you want to, that is...

[oldhippy]

Originally it would have been held in with shellac.  

You need to use a heat preventing compound, if you decide to solder using an iron. To much heat and the dial will crack. 

[saswatch88]

Yes i have seen dials with shellac, but it seems most of the American dials were tin soldered. Iam desperately trying to stay away from any kind of soldering because iam not the best at it, the closest i came is soldering wires together for vehicle electronics, and the occasional aluminum welding.

[saswatch88]

I don’t have a before pic but It would surprise you to know there was about 7 hairline cracks in this dial, the one on the left was the worst one but it was major difference, it looks more prominent in the pic but in person with naked eye you cant even see that one unless you get very close.

[ITProDad]

I don’t have a before pic but It would surprise you to know there was about 7 hairline cracks in this dial, the one on the left was the worst one but it was major difference, it looks more prominent in the pic but in person with naked eye you cant even see that one unless you get very close.

Very nice! I love American pocket watches.


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[jdrichard]

On 4/25/2021 at 8:02 PM, LittleWatchShop said:

Reinstalling the arbor in a mainspring must be a skill that is honed over time.  I am not there yet.

It always presents a challenge to me. 

I set the barrel on a bench block with a big hole in the middle so that there is plenty of room for the barrel pivot.

If the mainspring diameter at the barrel is less than that of the barrel (as I would expect it should be...) I find it hard to get the thing to seat without a number of tries.

Today, I decided to insert the barrel sideways to expand the spring and then rotate it into place.  Still a challenge, but it finally worked.  This was a new mainspring.

The barrel went flying several times...but not too far.

Maybe the experts here can share a trick of the trade.

I did a search of the forum but did not find a discussion on this--possible I could have missed it.

 

On 4/25/2021 at 8:33 PM, SuspectDevice said:

I was thinking a hollow staking set punch would be nice to hold the barrel arbor in place while I mess with the spring.

I've been looking at staking sets recently.