Double heat: Loosen screws secured with adhesive

Andreas Thaler · Mar 17, 2024

You often come across screws in cameras and lenses that are additionally secured in the thread with adhesive.

The manufacturer wants to ensure that the connection holds and is durable, for example on the bayonets of the camera and lenses.

As useful as this measure is, it is difficult to loosen such screws without damaging the screw head profile by overtightening. In the worst case scenario, the screw can no longer be loosened.

Loosen the adhesive bond

Common methods to loosen the adhesive bond are to use solvents such as alcohol and acetone, which are dripped onto the screw head, seeping into the thread and dissolving the adhesive.

Another method is to heat the screw, such as with a butane flame or the tip of a soldering iron. The bond then dissolves with heat.

However, the butane flame also heats up the surrounding area, which can have negative effects.

With the soldering iron tip, heat transfer to the screw is a problem because only part of the tip - however shaped - rests on the screw head. The heat transfer then takes a long time or does not occur at all.

Double heat

A solution for this can be solder. It creates a complete connection between the soldering tip and the screw head in a very short time and therefore transfers the heat without loss.

It is then removed with desoldering braid, which means a second heat transfer which supports dissolving.

Process

Apply solder to the screw head with the soldering tip.
Then remove the solder with desoldering braid soaked in flux and the soldering tip.
The screw can hopefully now be unscrewed easily with the screwdriver.
Even if the solder does not bond with the screw head, the resulting solder ball should transfer heat to the screw head.

I will try this on the next occasion

+++

All information provided without guarantee and use at your own risk.

BrianShaw · Mar 17, 2024

For clarification, please: is this a hypothesis or a proven technique?

Andreas Thaler · Mar 17, 2024

BrianShaw said:
For clarification, please: is this a hypothesis or a proven technique?

I will try this on the next occasion

The former

I just thought of it while I was dozing.

But it follows what happens when soldering.

BrianShaw · Mar 17, 2024

The reason I asked is that posting hypothetical and unproven methods are quite contrary to the philosophy of building an archive of proven repair methods. This is one way that internet rumors begin.

Andreas Thaler · Mar 17, 2024

BrianShaw said:
The reason I asked is that posting hypothetical and unproven methods are quite contrary to the philosophy of building an archive of proven repair methods. This is one way that internet rumors begin.

I do not think we are building an archive here, at least I'm not.

Rather, methods are presented, discussed and it is up to everyone whether to imitate it or not. This responsibility should not be taken away from anyone, see also my standard disclaimer.

And what are proven repair methods anyway?

You will find few, there are pros and cons for almost everything.

Take a look at the technical forums, e.g. electronics, rarely are there such fierce arguments.

Rumors on the Internet:

Your own practice and knowledge can help against this. Basically you have to verify every piece of information, there is no authority in place that tells you what is right or wrong.

Andreas Thaler · Mar 17, 2024

By the way, I also think it is necessary to critically examine tips and advice even from recognized experts. They may be wrong or may not know what my specific local conditions are.

For example, in a recent project I followed the advice in an - excellent - tutorial to remove a gear. This meant that the mechanism was no longer usable.

I didn't have to do it, it was my own decision.

BrianShaw · Mar 17, 2024

As you wish. Good luck with this experiment. I look forward to your report on the efficacy of your idea.

Andreas Thaler · Mar 17, 2024

BrianShaw said:
As you wish. Good luck with this experiment. I look forward to your report on the efficacy of your idea.

What do you think of this suggestion? Where do you see advantages/risks?

I would be interested in your opinion on this.

BrianShaw · Mar 17, 2024

Well, thanks for asking. My first thought was that if this was a viable option then it would have been already a recognized technique. I didn’t want to be rude and uninvitedly offer skepticism.

It’s not obvious to me that extending the duration of lower heat level, which seems the mechanism of this proposed technique, is sufficient to break the bond. Two applications of a soldering iron (without the solder) might be just as, or more, effective. I generally use solvents since they work quite well. Heat is a more “brute-force” technique in my opinion.

On another note, though… it’s quite amazing what our brain does as we sleep. My best ideas came in dreams. Some of my worst ideas, too.

Andreas Thaler · Mar 17, 2024

BrianShaw said:
Well, thanks for asking. My first thought was that if this was a viable option then it would have been already a recognized technique. I didn’t want to be rude and uninvitedly offer skepticism.

It’s not obvious to me that extending the duration of lower heat level, which seems the mechanism of this proposed technique, is sufficient to break the bond. Two applications of a soldering iron (without the solder) might be just as, or more, effective. I generally use solvents since they work quite well. Heat is a more “brute-force” technique in my opinion.

On another note, though… it’s quite amazing what our brain does as we sleep. My best ideas came in dreams. Some of my worst ideas, too.

But no, I'm happy when there are reactions to my posts

Using heat to loosen screws secured with adhesives is not a new idea and has already been discussed here. Also using a soldering iron for this.

I don't think I'm the first to think of solder for better heat transfer. But it is obvious that a soldering tip together with solder transfers the heat better to the soldering point, in this case the screw head. Because the heat transfer area is significantly larger. In addition, the heat is mainly limited to the screw and its threads.

Andreas Thaler · Mar 17, 2024

BrianShaw said:
It’s not obvious to me that extending the duration of lower heat level, which seems the mechanism of this proposed technique, is sufficient to break the bond.

On the contrary.

Of the approximately 340 degrees Celsius (644 degrees Fahrenheit) soldering tip temperature, the majority of it should reach the screw head when adding solder.

„Hotter, but shorter“ is the motto. Metal is generally a good conductor of heat.

250swb · Mar 17, 2024

I've used heat from a soldering iron to remove stubborn screws with no ill effects. Screws on cameras are generally gummed up rather than corroded and rusty, and some gentle heat can soften the gummy old grease or glue long enough to get the screw out before the gum sets again. Heat and then a drop of WD-40 can also work. However common sense is required not to use heat near plastics and paint, and it doesn't need to be at a high soldering temperature, in fact using a low melt solder on the tip lowers the temperature used and transfers the heat faster as per the idea in the OP's original post. I've not had solder actually stick to the screw though, that is curious as generally speaking steel doesn't solder, the solder just bobbles off it.

BrianShaw · Mar 17, 2024

I think you'll find that the tempreature of solder generally is under 200 degrees Farenghiet and the temperature range of therad sealant is quite a both more, as is the temperature of a soldering iron. Your hyposthsis seems to be that you can get more localized or better heat transfer. That might be so but the heat might (probably?) will not be sufficient tfor the task at hand.

EDIT: see post #14!

BrianShaw · Mar 17, 2024

Andreas Thaler said:
On the contrary.

Of the approximately 340 degrees Celsius (644 degrees Fahrenheit) soldering tip temperature, the majority of it should reach the screw head when adding solder.

„Hotter, but shorter“ is the motto. Metal is generally a good conductor of heat.

We were typing at the same time...

Then what is the benefit of putting solder on and taking it off?

Andreas Thaler · Mar 17, 2024

BrianShaw said:
I think you'll find that the tempreature of solder generally is under 200 degrees Farenghiet and the temperature range of therad sealant is quite a both more, as is the temperature of a soldering iron. Your hyposthsis seems to be that you can get more localized or better heat transfer. That might be so but the heat might (probably?) will not be sufficient tfor the task at hand.

EDIT: see post #14!

Sorry, but I can't melt solder at 200 F when soldering.

From 644 F for lead-free solder, approx. 464 F for lead-containing solder.

I haven't had any other experiences.

Light Capture · Mar 17, 2024

As always, try acetone first.

Heating the screw head is a proven method that works in two ways. If screw is stuck there's almost certainly something between the screw and the thread.
1. If there's rust, it will expand the screw at different rate compared to the metal it's screwed in.
2. If there's some kind of the thread locker, there will be different expansion rate plus softening of the thread locker.

There has to be efficient heat transfer involved. If there's no efficient heat transfer, heat will transfer slowly and spread in surrounding material without causing expansion.
Strong soldering iron with a tip that will transfer maximum heat in short time is recommended. When done right you can hold the surrounding material with your fingers without any excess heat.
Heating for a long time won't do much. If done properly and there is rust or thread locker you'll be able to hold even a couple of cm parts to release screws from them.
With this in mind, cheaper soldering irons have tremendous temperature falls at first contact with larger mass. It can be longer than 15-20s. This will result in poor release performance since the surrounding mass temperature will catch up.

If someone used stronger thread locker on it it could need 350-450C for release.

If everything fails there's hot air soldering station. With it temperature and air flow as well as the shape of the airflow can be regulated. You can also match it to metallurgical properties of the material if it's sensitive.
If you heat it too high it will temper the material and it will change color. All sensitive parts have to be removed. This is usually done on larger bolts and nuts.
On the other hand if you need 150C it will get there easily and keep that temperature without overheating. The same method at lower temperature that won't damage surroundings is helpful for leatherette and adhesive removals. Most of them soften at lower temperatures but if heat gun is used there's no good temperature control.

Last resort is to drill out and thread on the milling machine.

There are screw extractors for watchmaking but they can't be used on cameras most of the time since they're very small.

Either method takes time and patience and most of the time several tries.

Proper screwdrivers and screwdriver maintenance/sharpening will also prevent many of these secondary methods.
For example one should have a few of 2mm (or any other required sizes) sharpened differently. Also made from different materials. It makes all the difference.

Andreas Thaler · Mar 17, 2024

BrianShaw said:
We were typing at the same time...

Then what is the benefit of putting solder on and taking it off?

If I have solder on the screw head that has bound, I can no longer insert the screwdriver into the screw head profile. So it has to go.

If I do this with desoldering braid and flux, it's thorough and quick, with the advantage that heat once again comes onto the screw. You can also use the desoldering suction pump.

BrianShaw · Mar 17, 2024

Andreas Thaler said:
Sorry, but I can't melt solder at 200 F when soldering.

From 464 F for lead-free solder, approx. 644 for lead-containing solder.

I haven't had any other experiences.

Yep... solder is not a unitary thing; there are different types with different chanracteristics.

Andreas Thaler · Mar 17, 2024

Glued bayonet screws in MF Nikkors are well-known examples.

Richard Haw wrote a tutorial about this:

Repair: Nikon Bayonet Screws (Video)

Hello, Everybody! Spring is here! It is definitely getting warmer and while that is definitely good news, the bad news is hay fever is also in season! I suffer from hay fever just like many people …

richardhaw.com

BrianShaw · Mar 17, 2024

Additionally, it's not just expansion/contraction that breaks the bond... it's also bringing the thread locker to a temperature where the bond fails or using solvent to fail the bond. So that depends on the characteristics of the thread locker, too. Collateral damage is always a concern, with heat as well as with solvents.

What did Richard Haw write that supports this hypothsis? Yes, thread lockers are used and can be a challenge to un-do. I seem to recall him recommending solvent solution rather than heat. And good/proper screwdrivers.

Andreas Thaler · Mar 17, 2024

Andreas Thaler said:
Sorry, but I can't melt solder at 200 F when soldering.

From 644 F for lead-free solder, approx. 464 F for lead-containing solder.

I haven't had any other experiences.

Correction, I swapped the values.

Andreas Thaler · Mar 17, 2024

BrianShaw said:
Additionally, it's not just expansion/contraction that breaks the bond... it's also bringing the thread locker to a temperature where the bond fails or using solvent to fail the bond. So that depends on the characteristics of the thread locker, too. Collateral damage is always a concern, with heat as well as with solvents.

What did Richard Haw write that supports this hypothsis? Yes, thread lockers are used and can be a challenge to un-do. I seem to recall him recommending solvent solution rather than heat.

You can't always get anywhere with solvents. Not even with heat. But both methods double your chances.

At least that's what happened with my lens repair projects where screws refused.

Sometimes nothing works at all.

BrianShaw · Mar 17, 2024

Andreas Thaler said:
You can't always get anywhere with solvents. Not even with heat. But both methods double your chances.

At least that's what happened with my lens repair projects where screws refused.

Sometimes nothing works at all.

You are not alone. That's why I'm looking forward to yorr experiments and report on the double-heat solder technique.

Andreas Thaler · Mar 17, 2024

BrianShaw said:
What did Richard Haw write that supports this hypothsis? Yes, thread lockers are used and can be a challenge to un-do. I seem to recall him recommending solvent solution rather than heat. And good/proper screwdrivers.

If a screw is difficult to remove, use a soldering bolt, heat the screw until it is too-hot for you to touch. Doing this will soften the compound and this will enable you to unscrew it without damaging the head.

Fundamentals: Screws and Drivers (1/3)

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richardhaw.com

For me, Richard is an expert as I see his instructions confirmed by my own experiences.

BrianShaw · Mar 17, 2024

The older Nikkors have the tendency of having excessive amounts of Loctite used on the bayonet screws (and elsewhere) and you should be very careful when working with these. There will be times when you would need to put a drop of acetone on the screw to soften whatever they have used and just apply the correct pressure and torque to loosen them. I sometimes heat the screw with a butane torch to burn whatever sealant they used on the screw but since I started using the longer shafted VESSEL drivers, I don’t find this necessary anymore. This screw burning practice is a very common hack for auto mechanics (specially on rusted screws). There will be times when the only way to loosen a screw is to heat it but keep that to a minimum.

He also says (added for increased clarity). I agree that he generally has great advise.

I don't see him recommending soldering and unsoldering... that is specifically what I was asking.

Double heat: Loosen screws secured with adhesive

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