Broken Stem in Crown

[Bonefixer]

I bought a 'spares/repairs' Tag Heuer chronograph from eBay to fix up. The watch runs, but was sold as the crown wasn't connected to the movement. 
 

I've fixed it up just fine, new pusher to replace a broken one and a new stem plus generic crown. I'd like to salvage the original Tag Heuer crown with the logo, but I can't see how to remove the broken bit of stem. It's broken flush, and is presumably threadlocked as well. There's no way I'll be able to drill it out, or use a reverse cutting broken screw removal device. 
 

Any suggestions? solvents plus ultrasound? Heat? There's literally nothing to get hold of to unscrew. 

[Neverenoughwatches]

22 minutes ago, Bonefixer said:

I bought a 'spares/repairs' Tag Heuer chronograph from eBay to fix up. The watch runs, but was sold as the crown wasn't connected to the movement. 
 

I've fixed it up just fine, new pusher to replace a broken one and a new stem plus generic crown. I'd like to salvage the original Tag Heuer crown with the logo, but I can't see how to remove the broken bit of stem. It's broken flush, and is presumably threadlocked as well. There's no way I'll be able to drill it out, or use a reverse cutting broken screw removal device. 
 

Any suggestions? solvents plus ultrasound? Heat? There's literally nothing to get hold of to unscrew. 

A popular method is to dissolve the bit of broken stem with acid.  That depends entirely on what the materials are to be immersed. If the stem is stainless steel then i dont think acid will take effect or much of. Any steel in the crown might be damaged. Try other mechanical methods first that you suggested, see if you can drill into the stem bit to make anchoring hole for using a screw removal method.

[Klassiker]

Use potassium alum dissolved in water. Immerse the crown in a small amount overnight. Add more powder to reactivate if necessary. If the crown is stainless steel, it will not be harmed. It might get a cloudy surface which polishes off easily. The remains of the stem will dissolve. This is a much safer method than mechanical means.

[Bonefixer]

I've ordered some Alum powder.  I'll possibly try it on a bit of stem first - the bit I extracted from the movement.

I'll report back!

[Klassiker]

11 hours ago, Bonefixer said:

I'll possibly try it on a bit of stem first

Good idea. Dissolve as much powder into the water as it will take. Keeping it warm will dissolve the stem faster, but isn't essential. The reaction takes hours rather than minutes.

[Bonefixer]

On 3/18/2024 at 6:59 AM, Klassiker said:

Good idea. Dissolve as much powder into the water as it will take. Keeping it warm will dissolve the stem faster, but isn't essential. The reaction takes hours rather than minutes.

Well it worked, but took days rather than hours. Not sure all the broken stem is out, but there’s now enough thread to screw onto a new one.