Removing extremely stuck screws

[AshF]

This is starting to sound like you sending me for a "long weight" or a "left handed screwdriver".

[praezis]

Surely no joke. Working agent is phosporic acid, a maior ingredient of Coke.

Frank

[nickelsilver]

Surely no joke. Working agent is phosporic acid, a maior ingredient of Coke.
Frank

I mentioned to my old boss that phosphoric acid is in coke and he laughed and bet me 100 bucks I was wrong. He grabbed a bottle of phosphoric out of his chemical cabinet to show me how degraded the label was, no way we ingest that. Easiest 100 bucks I ever made.

I stick to water and beer for ingesting.

[Nucejoe]

With the exception of jewel- chaton and hairspring, I soak all else in coca cola. diet cola is prefered for the lack of suger since suger will crystalize inside the chatons.

The coke penetrates like oil and if brushed with powdered detergent cleans incredably well.

Try it on a scrap movement to see the diference. 

You will be surprised.

[AshF]

2 days of soaking and they're still stuck.  I've just ultrasonically cleaned it (whole) so will now leave it in essence of renata overnight to displace any water.  Luckily, I removed the balance and pallet.  It's the barrel bridge, train bridge and screw for setting lever that are stuck.  So, a little bit of heat next right?  Then I get my drill out.

[Nucejoe]

This makes I the surprised party.  Trying other solutions wont hurt.

Heat is to be applied directly to each screw by soldering gun and  immediately followed with a quench in liquid of your choice, I drop in ice water, reheat to get rid of all moisture , reapply penetrating oil.

No tapping on the screw, only if you get to the very last resort( alum) in case screw head pop off and replacement screws are available.

Good luck pal.

 

[rodabod]

I’ve never heard of anyone quenching a screw after heating it for the purpose of loosening it. You shouldn’t be heating it to the point where you can quench it to set the temper. Unless you are maybe suggesting that the sudden change in temperature helps to break down the bonding between the screw and screw hole. 

[Nucejoe]

I guess you first interpreted my statement by metalurgical definition of quench.

The later part of your statement well expresses what I had in mind, we are seeking an expansion/ contraction through quick temperature change of the screw itself.

[rodabod]

Ah, ok. I understand what you mean now. I don’t have any experience of doing that - I will remain sceptical, but I’m open to new ideas. 
 

The way I normally work these days is to try getting the screw out perhaps with the aid of penetrating fluid, sometimes a light tap with a hammer, etc. But ultimately, I find that if they are completely bonded with corrosion then there are times when they simply will not unscrew.

What fills the extremely small void between the screw head and screw hole (iron oxide) cannot be removed, so you end up with what cyclists occasionally encounter with bike seat posts being bonded into the frame seat tube with no option but to destroy the seat post. 

 

[Waggy]

I have had good results using a penetrating oil - this product is built for the task of removing stuck screws and bolts, unlike coke or WD40 or....??? just apply a small amount using an old oiler and let it soak into the screw/hole overnight. You may need to apply several times but eventually it will do the job without stressing the components and reducing the risk of shearing off the screw head. You can buy a big can of the stuff for only a few $$, so a good investment, why make life hard for yourself, use the proper tool for the job.

I have seen the effects of coke on parts, whilst it does attack the rust that binds these parts together it also attacks the base metal of the entire part, I have used a scanning electron microscope (SEM) on parts after soaking in coke and they look like the surface of the moon where the acid has arbitrarily eaten into the steel. Maybe you can't see this with regular magnification or the naked eye, but over time they are initiation sites for future pitting/stress corrosion and picking up debris = erosion. Why would you risk this if there are better options out there?

There is a phenomenon called galling where a thread is damaged (usually) by a small amount of debris or manufacturing defect, this initiation point then further damages the thread causing a chain reaction and heat - finally reaction results in a process called cold welding where the steel essentially fuses together, then the parts are irretrievably 'stuck' together. Galling is seen in high Cr steels - so stainless steels (Cr >12%) are a prime suspect for this (note 316L SS is +/- 16% Cr) and sometimes this is why these threads are coated with copper or other softer metals to prevent galling.

Therefore, if the screw in the original post is rusted in place then the best option would be several attempts using penetrating oil, if this is not successful then there is a good possibility that the thread is galled and nothing will help you other than drilling out the screw if this is an option.

By the way, I am basing the above from the perspective that I am Chartered Mechanical Engineer and Fellow of the Institution of Mechanical Engineers with over 25 years of Engineering experience.

Edited February 28, 2023 by Waggy

[Carlo]

So... I stumbled upon this thread as I have a rusty dial foot screw embedded in a ladies FHF movement. As of the moment I have cleaned the rust from the slot and filed the screwdriver to best fill the slot. I've tried penetrating oil (PB Blaster) and heating a probe that I held against the screw (don't know how much heat that actually transferred to the screw). Since the dial, cannon pinion, center wheel, and everything else on the dial side remain attached to the main plate soaking in cola is not a option (as delightful as that sounds). 

Is galling (as described above) seen between disparate metals -- ie, between a steel screw and a brass dial foot, or the nickel plated brass of a main plate? Or is it more of a galvanic type corrosion? 

In any event I had to buy a new soldering iron with a tip small enough to get to the screw head recessed into the main plate. That'll be tomorrow's game, let the penetrating oil work another night. 

Any other ideas out there?

[Waggy]

Galling and galvanic corrosion are different things. Galvanic corrosion is an electrochemical reaction between 2 dissimilar metals, whereas galling is a physical reaction between two similar or dissimilar metals. I think heating the screw was the opposite of what you should be doing, this would cause it to expand making it (temporarily) tighter. In the past I have put a watch case into hot water from the kettle in a coffee cup (inside a plastic bag to keep it dry) then used an ice cube on the stuck case back, thereby enlarging the female thread on the case and shrinking the male thread of the case back allowing me to unscrew it. You could heat the part as I describe, but an ice cube wouldn't work in your case... But thinking maybe one of those freeze skin tag pens you get in the pharmacy could cool the screw and shrink it??? Never tried this and only just thought of it, so let's see what others think?? Maybe the cooling pen idea would be too cold and make the screw too brittle and prone to shear off the head??

Perhaps you could place a metal rod in the freezer to cool it, then hold the rod against the screw to transfer the cold? Or even put the screwdriver in the freezer for the same effect, but maybe the screwdriver would have too little surface area to transfer enough cold before it returned to room temperature??

Something like this:

[Carlo]

I would try cold but since there's no way of securely holding the main plate other than with my fingers I am reluctant to go this route.

Another night of penetrating oil and heat this morning provided no results. My Bergeon screwdriver's shaft was flexing and torquing so I fabricated a much stronger one from an old cheapie eyeglass screwdriver. Still no luck. 

At this point I see no other option than to drill out the dial foot. It's staring at me. At least I can support the movement adequately for this operation. 

[canthus]

Quite often penetrating oils are simply very thin oils with perhaps a metal de-activator additive or also de-rust agent.  The thinner the oil the more it may be able to penetrate the gaps.  I have used de-odorised kerosine with success. Readily available as bbq lighter fuel!

I also understand that a fine pointed solder iron tip does not transfer heat very effectively and normally requires a high heat setting to get it to melt solder.  A more robust tip would impart more heat, but over a greater area.  What about putting the screwdriver in the freezer and then using it on the hot screw.  The screwdriver would tend to draw the heat from the screw first and hopefully contract it enough to loosen it up.  Just an idea.  Being able to push down hard on the screw often helps. Not easy with a dial foot screw!

[Carlo]

#70 drill bit in a pin vise. Took all of 90 seconds to drill out enough of the dial foot that I could get the dial off. Still have a decent amount of dial foot remaining, probably enough to stabilize the dial. 

I might leave the screw in place but I may alum it out, just to teach it a lesson.

[Nucejoe]

If you had access to the free end of dial feet, tapping on it has always worked. 

[Carlo]

I did have access, and I did try pressing on it, but I probably couldn't get enough force on it. Anyway it's done, thanks to all who offered suggestions!