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Stem broken off in crown dissolved with vinegar...now what?

13K views 17 replies 12 participants last post by  nomad1001 
#1 ·
Hey all,

I bought a watch with the tap 10 stem broken off right at the end of the crown post. While I could have simply acquired and fitted a new crown, the crown is signed and I wanted to keep it. So, I tried removing the stem.

There wasn't enough protruding to grab with pliers. I tried (unsuccessfully) filing a slot in the stem to back it out with a screw driver. I even took it to a local shop, but they said they couldn't remove it.

I read soaking the crown in vinegar would dissolve the softer steel of the stem, but not harm the stainless steel. I gave it a shot and after several weeks it worked, but now what?

The vinegar has evaporated and I've cleaned up the crown with rodico and pegwood. Do I need to do something to ensure the vinegar is neutralized? Do I need to replace the gasket (it's a waterproof crown)? What other questions should I be asking?

Taking a step back, is this a watchmaker accepted method for solving this problem?

I appreciate your help,

Doug
 
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#6 ·
You need alum powder, did a write up on it recently here Extracting a broken screw from a watch/bridge plate ? Alum Powder | Watch In Progress | Watch Repair & Servicing Blog

Works exactly the same way on crowns.
I tried purchasing "alum powder" but found there are several different formulas and need to be certain which is correct for the removal of a steel stem broken off in a non ferrous crown? I tried a magnet on the crown but I believe the stem piece is the only part attracting the magnet. It's a Disney Ingersoll China quartz watch with a Miyota co. 7T35 movement and the crown has the Disney logo embossed on it. I've found several correct movements with stem but would like to keep the crown?
 
#8 ·
...I read soaking the crown in vinegar would dissolve the softer steel of the stem, but not harm the stainless steel. I gave it a shot and after several weeks it worked, but now what?...
Doug
Rinse the crown with water. Then you might rinse with alcohol (which will remove almost all of the water) and blow dry. You may need to further clean/dress the threads with a size 10 bottom tap. Then get your new stem and fit it to the case & crown.

As for alum...you have already dissolved the stem with acetic acid...so you shouldn't need it...

Regards, BG
 
#10 ·
The things you learn............

Apart from the novelty I was also intrigued as I use an alum block after blade shaving. It is also used in stypic sticks to stop bleeding from small cuts.

If anyone is interested here is a wiki describing the different alums.

https://en.wikipedia.org/wiki/Alum
 
#13 ·
Not tried Vissin because i don't see the point in throwing money at Bergeon when the chemistry involved is understood well enough to take your pick of household chemicals.

Essentially, it doesn't matter what liquid you use, if you have a combination of steel and most other metals used in watchmaking in contact with each other and submerge them in an electrolyte the steel will corrode and the other metal won't be affected. It all depends on their relative position in the Galvanic series.

All metals and certain non-metals have an electropotential. This is a measure of their willingness to either give up or receive electrons. The galvanic series rates them from "most positive" to "most negative" and, in the situation above (in contact and submerged in electrolyte) the more negative metal will corrode.

The electrolyte used doesn't affect that much - the order can change slightly in different solutions but not enough to affect us with watch parts. So you can use vinegar (acetic acid), any of the alums, something like sulphuric acid, or even salt water. The only difference will be the speed of the reaction - obviously sulphuric acid will react a LOT faster than seawater!

Alum is popular because it's easily available, cheap, safe, and reacts at a reasonably controllable rate.

Ordinary carbon steel is pretty low on the list - below all precious metals, copper, the various brasses, and stainless steel. So it'll corrode leaving any of those unharmed. The only exception you might come across with watches are aluminium crowns - don't try these because the'll corrode before the steel!

Science, don't ya just love it? :)
 
#14 · (Edited)
I'm not sure how to determine if the crown is aluminum or if it's stainless steel? Your saying that vinegar will not effect (etch) either aluminum or stainless steel but alum will etch aluminum? I've purchased the correct stem but haven't attempted dissolving the broken stem yet. I'm thinking if vinegar is used for even 2 weeks to dissolve the metal stem then soaking the crown in baking soda would neutralize the vinegar traces then blow it out and soak it in rubbing alcohol to remove all the moisture followed by blowing out again? I'm just not sure what vinegar will do to stainless steel or aluminum and this is a signed crown that I have to preserve?
 
#15 ·
I've just bought a super rare Pulsar with the YM62 movement and its the one with the intricately engraved case and super massif "UFO" crown which appears to have snapped.

Now to find out if the crown itself is safe to alum or not as stems are easy to acquire.
 
#17 ·
I've got a rotary tool and various drills but nothing so fine. I take it that a tap 8 means its a 0.8mm diameter? I have asked Seiko UK if they can let me know if the crown is full stainless steel as I would like to do the alum trick.

Am super pleased with this crazy looking Pulsar, its super rare in the chocolate and that futuristic overengineered look which made me snap it up almost under a minute it showed up in my ebay feeds.

15929255
 
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