DIY safety signal mirror

[emoreira]

Hi, just to share with you my DIY safety signal mirror.
Done with a 304 stainless steel plate 100 mm x 70 mm (4" x 2,75"), 1 mm thick.
Done a center hole 8 mm (5/16") and a corner hole 5 mm (3/16") for the lanyard.
The reflecting side was sanded with 150 sand paper and then polished with Autopolish(R).
I can see my face reflected in the reflecting surface.
Tested at home in the street and can be seen 100 mts away ok.

 

[Captain CCR]

I find a cd or dvd is just as good , easy to replace

 

[emoreira]

Yes, could be, but it's not so comfortable to carry in your BCD.

 

[CheddarChick]

Very nice...

 

[D_B]

I find a cd or dvd is just as good , easy to replace

That's been tested and CD's make very poor mirrors , they may be better than nothing but that's hardly a recommendation to use one instead of a mirror


emoreira ... good work! ... I have a polished piece of stainless in my truck much like what you have made (in my BC I have a plastic mirror)

Aiming .. you make a V with two fingers of one hand, hold arm out and put intended target between them, and flash reflected sunlight on/between fingers .. flashes are aimed squarely at target

 

[reefduffer]

Three comments: First, I echo D_B, this has been discussed a number of times here on SB, a CD is not a good substitute for a real signal mirror.

Second and third, to the OP: Here is a real signal mirror, it happens to be the one I own: Signal Mirror $6.00. I note you're in Argentina, and that price is ex shipping, but still... How much work do you put into a DIY substitute for a $6 piece of safety equipment that works better than what you're building?

Which brings me to the third point. This signal mirror, and others like it, have some non-obvious technology called a "retroreflective aimer" that makes them more effective than it might seem until you understand it. There is more to it than just a sighting hole.

When you have your little mirror at arms' length, looking through the sight hole at that plane or boat a mile or ten away, and when it's actually reflecting the sun at the target, the bevel ring around the hole will flash brightly back at you. This feedback makes a very substantial difference in whether you can actually do that sighting alignment effectively, compared to just a sighting hole.

The military etc. abandoned "foresight aiming" mirrors when the retroflective ones become available. See Signal Mirrors - Page 4 - Hammock Forums : Your Number One Hammock Community among other descriptions.

Does your DIY mirror have that property?

 

[D_B]

Mine does, and it's remarkably effective but it does have the drawback of looking through that little hole
... and, it's not absolutely essential using the V finger aiming technique (thanks for that Walter)

 

[emoreira]

Three comments: First, I echo D_B, this has been discussed a number of times here on SB, a CD is not a good substitute for a real signal mirror.

Second and third, to the OP: Here is a real signal mirror, it happens to be the one I own: Signal Mirror $6.00. I note you're in Argentina, and that price is ex shipping, but still... How much work do you put into a DIY substitute for a $6 piece of safety equipment that works better than what you're building?

Which brings me to the third point. This signal mirror, and others like it, have some non-obvious technology called a "retroreflective aimer" that makes them more effective than it might seem until you understand it. There is more to it than just a sighting hole.

When you have your little mirror at arms' length, looking through the sight hole at that plane or boat a mile or ten away, and when it's actually reflecting the sun at the target, the bevel ring around the hole will flash brightly back at you. This feedback makes a very substantial difference in whether you can actually do that sighting alignment effectively, compared to just a sighting hole.

The military etc. abandoned "foresight aiming" mirrors when the retroflective ones become available. See Signal Mirrors - Page 4 - Hammock Forums : Your Number One Hammock Community among other descriptions.

Does your DIY mirror have that property?

I've been searching those type of mirrors here in Argentina with no luck.
Safety signal mirrors are not diving exclusive. They are also used for general nautical use.
Not only the "almost the same mirror" I've done can be purchased here but also the price is within 30 to 50 US$ here.
I've done mine with a piece of Stainless steel I had at home in less that 3 hours.

If it happens I can go again to the US in the future, I will try to get one.

 

[knowone]

Just polish yours every so often emoreira.

Very good.

Don't the cd players get rusty?

 

[reefduffer]

I've been searching those type of mirrors here in Argentina with no luck.
Safety signal mirrors are not diving exclusive. They are also used for general nautical use.
Not only the "almost the same mirror" I've done can be purchased here but also the price is within 30 to 50 US$ here.
I've done mine with a piece of Stainless steel I had at home in less that 3 hours.

If it happens I can go again to the US in the future, I will try to get one.

Emoreira,

If I had to pay $30-$50 for a "real" signal mirror, I might consider alternatives as well. I thought Argentina was a little more ... first world ... than that. If you can get scuba gear and air fills ... I'm not trying to pick on you, just a little surprised. Do what you have to. A polished piece of metal, or a CD, is better than nothing.

I'm posting again I had time to do a little more looking around the web for references, found some good stuff, and thought I'd capture it here for future reference. Scubaboard being what it is, the question will arise again (and again, see below).

Here is a discussion of how a retroreflective signal mirror works, in the context of pretenders: WARNING: Phony Glass Signal Mirrors - EQUIPPED TO SURVIVE (tm)
Besides a very accessable explanation, with diagrams, this has a pointer to a pdf version of the 1951 US patent of Hunter, 2557108, "Signal Mirror". (If that equipped.com site goes away someday, you can get online access all US patents for free at US Patent Full-Text Database Number Search ). The Hunter patent seems to be the basis of most modern retroreflective designs, but there are earlier designs referenced within the patent.

For those who want it easier than reading a linked article, and for posterity, my simplified summary, no diagram: There's a loose grid of fine wires surrounding the sight hole, bonded to the rear surface of the mirror. Bonded to the wires are numerous small retroreflective beads, like the ones on safety tape. These result in a reflected beam back towards the sun. A fraction of that reflected beam bounces off the interface between the front surface of the mirror and the air. The geometry is such that that re-reflected beam is colinear with, but in the opposite direction of, the main mirror reflection of the sun (the one you'd like pointed at the search plane). So if you can see the plane through the hole, and at the same time see the bright flash of the re-reflection around the hole, you're aiming the main reflection at the plane.

That same site has a discussion of signalling devices in general, and mirrors in particular, at EQUIPPED TO SURVIVE (tm) - SIGNALING GROUP . Some excerpts from that relevent to previous discussions in this thread:

In tests a CD proved .... not even 50% compared to a small 2 x 3 mil-spec plastic signal mirror. ... Report of ... Civil Air Patrol, the conclusions were, "that "victims" who had never used a signal mirror (with the aiming hole in the middle) were able to use them effectively, while CD's (AOL etc.) are useless as signal mirrors."

There's also discussion of the negatives of polished metal mirrors, too long to excerpt, but basically, not as reflective, corrodes over time, either heavy or subject to distortion, and has no retrorefleflective aimer.

In searching scubaboard, I found that this equipped.com site has been referenced here before, in 2004 http://www.scubaboard.com/forums/ba...a-scuba-items-dont-leave-home-without-em.html and 2007 http://www.scubaboard.com/forums/accessories/179678-signal-mirror-evaluation.html . Who knows, maybe more. The retroreflective property has definitely been mentioned many more times than that, but I didn't really see an explanation of it.

That's the nature of scubaboard ... What to wear under a wetsuit? ... Do I need a knife? ... How can I use less air? ... . My purpose here is first to answer this one one more time, and be a reference to point to quickly the next time, and the one after that. And maybe add a little value by providing some more detail.