Dissolving broken screws

[skridlov]

I have a couple of bridges that need screws removing and know of, but haven't yet tried, a warm alum solution. Are most/all bridges steel-free or are some alloyed in such a combination that there's a risk to the bridge itself? Additionally I saw a reference to the use of concentrated citric acid (often used for removing accumulated limescale in washing machines etc) for the same purpose. Has anyone tried citric acid?

Thanks

Roy

[RyMoeller]

Never tried citric acid but I have dissolved several screws using alum, it works very quickly provided you keep the water warm.

Most bridges are plated brass but not all.  You can usually tell if a bridge is made of steel because it will be the same color as the steel components within the watch (pinions, ratchet wheel, screws, etc.).  Steel bridges are typically thinner than brass bridges and in my experience are usually found on the dial side (typically for the calendar works).

[transporter]

Yep ive used alum before, I set it next to the hot water pipe in an airing cupboard, left it overnight, (longer than needed) and screws were totally disolved 

[skridlov]

Thanks for the useful information.

"You can usually tell if a bridge is made of steel because it will be the same color as the steel components..."

That usually gives me pause for thought! I once used caustic soda to clean up an animal skull. It dissolved.

Roy

 

[rodabod]

I need to remove a screw from an IWC Cal 83 main plate. I've inspected the plate and believe that the banking pins are also steel..... I was considering only submerging part of the plate into the alum, but am led to believe that this will case a "tide mark" on the plate.

Is there a way I can safely seal the banking pins (in shellac for example?) or am I best just living with a tide mark?

[RyMoeller]

 

I need to remove a screw from an IWC Cal 83 main plate. I've inspected the plate and believe that the banking pins are also steel..... I was considering only submerging part of the plate into the alum, but am led to believe that this will case a "tide mark" on the plate.

Is there a way I can safely seal the banking pins (in shellac for example?) or am I best just living with a tide mark?

I've done it both ways without any issues.  Once I suspended the plate with a bit of copper wire so that only half of the plate was submerged in the alum bath in order to dissolve a screw without risking damage to a post which I was sure was steel.  The plate was silver plated brass and the alum bath didn't leave any marks on the plate.  In fact I've used the alum bath method on three occasions and it hasn't ever stained the plate.

Usually if there is a bit of steel on the plate which I don't want to be dissolved by the alum I'll cover the steel with silicone calk (like you would use to seal around a sink).  Since the calk is water proof, the alum solution will not be able to get at the steel underneath.  I usually apply the calk with an oiler under the stereo microscope.  It's important to make sure the steel bit is completely encased though because if it's not then the steel will be ruined by the alum bath.  The calk can be removed fairly easily with a bit of pegwood after the bathing is complete.

[rogart63]

Have a seiko 6117 plate in the alum bath right now. Did it the hard way and removed all steel parts before i dipped it in alum. So before i can put the movement back together again i have to put the threads back on the movement plate. I removed the balance jewel so hope i could get it back in the right position again. 

The threads for the trainwheel bridge are special inserts that are pressed into the movement plate. 

Can take some pictures. 

Have never seen any tide mark or something to the plates. But clean very good after as the crystal from the alum can still be there. 

Edited June 26, 2017 by rogart63