Locking Paint/Adhesive

I am not interested in anaerobic (Loctite) or 2-part adhesives.

Why not? As an example, the Loctite 248 Medium Strength Threadlocker Stick just requires hand tools to remove. If you want to lock after the joint is made how about locking up the existing nut with another nut, or just adding a drop of glue to the existing nut (or fastener). All of these are suitable for a number of applications, what is your application and special requirements.

Why not anaerobic? Excess anaerobic liquids do not harden, they stay liquid and migrate. A number of years ago, I was designing precision tape recorders. After several months, several tape guide mechanisms became rough. Our chemist found contaminant in the grease. A spectral analysis revealed that it was the Loctite. We had to recall hundreds of tape recorders, disassemble them, wash out all the grease, re-lube the bearings, reassemble, retest. We switched from using an anaerobic adhesive to a 2-part epoxy to secure the small bearings in their bore.

I currently use Loctite-242 to secure most of the fasteners in the electromechanical assembly. There are a few which are very close to optical elements and I cannot afford to have excess migrate onto the optics.

Why not a 2-part epoxy? I want to instill the practice of stripping each fastener as it is torqued. Coming back later and stripping all the fasteners at one time after they are torqued does not meet my criteria. Epoxy cure times are not compatible with the process I want to use.

If you are assembling then that's different. A standard locking washer or nut would be your best option. No mess, no fuss. Standard spring washers, star washers or Nylock nuts (nuts with a nylon insert that act as the locking mechanism) work great on your threaded fastenings, rod linkages, etc. It's only when you have a pre-assembled product or special mechanical fastening where I would suggest some sort of locking compound (for the reasons you have already mentioned), and it certainly wouldn't be a time-consuming two-part epoxy unless there were no other simpler alternatives. I cannot say I would recommend cyanoacrylates for an optics application either. There must be a compound out there that doesn't migrate or gas.

Why re-invent the wheel? Loctite does a bang-up job, and ultimately, isn't that what matters most?

If cyanoacrylates are off-side, then consider the Nord-Lock fastener (usual disclaimer).

http://www.nordlock.de/web/1_23_37.htm

Yes. A prick punch. Put three equally spaced punches around the interface between the screw and nut. I always put them in the nut, but the screw would work also. Put some muscle into this - you're deforming the metal.

Finger nail polish works well on small fasteners. Provides a security seal to show tampering. Dries quickly. Comes in many different colors. And a bonus if you run out while doing a job just ask the women around you. If you can handle the confused stare.

Still looking. I was given the idea of using corona dope, so I've ordered some and will give it a try.

Snave, has the corona dope worked ok for your application? If so could you pass on the product details, as the terminology seems to be different in the UK and I can't find any reference to it with supply houses here?

I would be interested to know why you rejected loctite 7400?

Thanks - Peter

Peter - The corona dope that I bought did not work as well as I was anticipating. Years ago, I had some corona dope that was brick red in color that was very viscous. The stuff I bought was nearly clear in color and not very thick when applied or strong ( resistant to sheer).

I did not look into Loctite 7400 as I was not aware of it. I gave up and modified the design so that there is room in the build up for lock washers.

If you try the Loctite 7400, let me know if it works for you.

To update my result on this topic, we have ended up deciding to use a cellulose based auto finish paint, CGX7 by

http://www.technicalpaintservices.com/

in the UK, as we found long term industry (servicing of rail signalling systems) use of this product for this application.

Peter.

Are you only interested in thread locking or sealing too ?

If it is only locking did you consider wire lock inserts ? These are regularly used by us in critical applications (eg inside Turbines etc where you can not afford the bolts to loosen up (reason obvious) neither can use the sealants at that temperature.

Sizes start from M6 onwards and as far as we have used is may be upto M48 (some times)

Also used as thread protection. Cost is not much and survives abuse, including multiple assembly and dismantling.

Do not have to have much stress in removal too

Think about it (and in case of sealing requirements - we use a second washer - eg copper washer, O ring or silicone rubber washers below the bolt head. (This is as per TRIZ - splitting the requirements into two parts)

I think I now what are you looking for.

Take a look:

http://www.ace-technik.de/schrauben-sicherungslack.4085.html

Regards