Can help with things that look impossible.

I recently received a brass caseback from a desk clock that one of our members thought I may be able to repair.
The upper and lower hinge pins of the door had been sheared at some stage, and an attempt to drill the steel pins out of the brass plate had not been all that successful.
So I had to get the remaining steel pins out of the brass without doing any more damage.
The pins were only 1.4mmØ, and although I had drill bits of the correct size I was unwilling to repeat the previous restorer's attempt. Any deviation of the drill bit would only cause further damage

Then a light bulb moment.

I remembered a couple of earlier posts by one of our watchmaker mentors where steel screws could be dissolved out of brass watch plates etc using a saturated solution of alum. So off I went.

I mixed up some block alum (after pounding it to a powder) and did a test dip for about 15 minutes.

A quick look showed that the bright steel had already gone black and the surface had started pitting.

Upper pin:



Lower pin:



So back into my home made alum bath (one of Annie's porcelain ramekins ) over a heat lamp to keep the solution warm. In the shot below you can see where the steel has disintegrated and is falling out.



So a good 48 hours with some cleaning of the holes every couple of hours and the result is nice clean holes ready for further repair.





Sorry I couldn't light up the holes any more than that, but they're only 1.4mmØ remember .

Thanks to @Archer for the original posts and for a couple of tips during the process.

 

Awesome!!

 

Glad it worked - it does take some time certainly, but I'm not in a rush with these things. I always have other watches in the shop I can be working on while a pesky part is being dissolved away.

 

I have used this method often. I use goldsmith’s pickle solution which does the job just as well. Most recently on a French crystal regulator. The owner found that the coiled iron gong was rasping on the glass case back. The coiled gong was sweated into a heavy brass block. He tried to bend the iron gong to clear the glass, and it broke off inside the brass block. It took about ten days for the iron stump to corrode away. After that, it was an easy fix.

 

Darn. I measured my drill bits ready to drill deeper holes and don't have any 1.4s so I had to order some more today so the project goes on for another day or two. Had to order the pivot wire anyway so no real time lost.

@Canuck, I'm interested in your "goldsmith's pickling solution". Any recipes?

 

First, you take Annie's ramekin and now, her pickles are in jeopardy!

 

This is bought (usually) in crystal form from sources that supply goldsmiths. It is dissolved in water. Goldsmiths use the solution to clean precious metal items after soldering. I use it to pickle gold items that have tarnished in areas that are difficult to get at with jeweller’s rouge and bristle brushes. Doubles for dissolving broken steel screws, pins, and whatever. It doesn’t harm non-ferrous metals, but leaves them nice and shiny.

 

So that was just about the coolest thing I've seen this week.

 

If you haven't seen it actually happen, here's a video that shows the alum doing it's job...

 

What, no cool soundtrack to go with that?