Do you think WD40 will destroy a Moly mirror?

This is my situation:

I bought this laser around 2 months ago 2nd hand, it’s around two years old. A few weeks ago I wanted to remove the laser head mirror 3 and clean it. Well, I couldn’t unscrew it to get it off.

So I had to remove the whole mirror assembly, removed all the screws and made a specialised tool (bottom right), but no matter how hard I tried, the mirror backing/holder/retainer thingy would not unscrew.

I actually don’t think it’s ever been unscrewed. I was able to access the front of the mirror and clean it. There was a film of grey coloured filth on there. So I tried lots of chemicals, softly, but ended up not getting anywhere.

At this point I didn’t care anymore, so I used Acetone. Finally the gunk slowly came off!! After about an hour of soaking the mirror face and wiping, I had a nice shiny looking mirror. So it looks like the mirrors in my laser are Molybdenum.

I reassembled-realigned the mirror, but this is not a long term solution because every time I want to clean the mirror, I have to take the whole assembly off, clean it, then re-align it again.

So, finally, I’m thinking, can I take off the assembly and carefully spray WD40 around the thread to remove the mirror? Could WD40 damage the mirror if it got on it? Considering Acetone does no harm, then perhaps it will be absolutely fine?

What say ye?

Mirrors 1 & 2 can’t be accessed or removed properly either, but that’s another story.

Whoops (idiot). Forgot to post the image:

I use a pair of snap ring pliers to remove tough ones. I don’t think your tool is strong enough.

You shouldn’t need to remove the whole thing to get at the mirror.

You clean the mirror it while it’s ‘in’ the head?


WD40 is a moisture displacer but I find its lubricating qualities are limited. Use equal parts of ATF (automatic transmission fluid) and acetone. Put a dab at the base of the treads with a toothpick. And use snap ring pliers.

I’m aware that you should be able to just unscrew the mirror in-situ without removing the whole assembly.

The tool I made is strong enough, but the pins aren’t long enough. But at this point, there is no way I would attempt putting that much strain on the whole mount - even if I had the correct tool.

The snap ring pliers sound like the way to go - after removing the whole mount. I’ll also use a small amount of ATF & Acetone as suggested.

I’m hoping the thread is not crossed - it wouldn’t surprise me considering that one of the spring retainer bolts was bent!! which could only have been done at the factory - not bent at the factory but someone using a faulty component didn’t care.

As far as mirrors 1 & 2 go, I have to cut inspection/access panels in the side of the chassis to properly adjust and remove those - lot’s of fun.

When you get the right tool and have it removed, then you can hang onto it and get it loose. Mine were snug but not really tight.

I’d try to get it loose without using any kind of chemistry, if possible.

My model was a 2021 and has an access panel on the left side. It was real handy when I replaced the motor mount/m2 assembly. It’s also nice as you can get your hand in there and adjust the mirrors more easily.

Good luck


If you do get that unthreaded, clean the threads and put a dab of anti-sieze on the threads. Galling could be a culprit, or the factory used some kind of thread lock compound (in which case some heat might help).

WD40 is a vegatable based compound. You can safely eat the stuff, so I doubt it will harm your mirror.

If you want to use heat to help loosen the screw, I suggest you use a soldering iron to localize the heat.

That’s funny, my WD40 container says “Contains petroleum products… harmful or fatal if swallowed”…


OK! Apparently I was misinformed. I will have to vet this kind of information from now on.

Thanks for the heads up.

Steve K.
Can you message me in any way?
I have some tools for ring removals that don’t fit my current setup.
Happy to pass them on