Lens Thickness

[Packhorse]

Yep, there is always the step lens design. And I guess you could also machine a few mm from the thread on the head.

The thickness of the lens will always be the weakness in a maglite but also the fact there is no Oring behind the lens, just one in front.

After that the next weakness is the choice of cable gland then ( and its a long way back) the strength of the body.

 

[Flo1]

How about laminating two glass lenses using a clear epoxy?

 

[Packhorse]

I tried that using acrylic glue which is very clear. It didnt stick. Perhaps with the right glue it will but getting a clear glue is hard. I wouldnt bother. I cant see it being significantly stonger than a single piece of glass twice the thickness.

 

[Klem]

Mentioned earlier, glass lenses flex a lot less than synthetic lenses...then they break!

I first started out using 4mm glass, and according to the local glazier 52mm circles are pretty small for his cutter and often the edges were a little chipped. Didn't seem to affect anything once the glue went on however. I then went 5mm thick, 114mm diameter for this larger reflector on a 35W HID and bingo, it cracked and flooded at 20Mts, on its maiden voyage...DAMN!

After that I've been using Perspex ever since. Thinnest they stock at the glazier is 6mm, which I suspect is overkill for the air depths I dive. It is cheaper than glass but with slightly less light transfer they tell me. I can't tell the difference to be honest.

One thing you need to be careful about is heat forward onto the lens, especially when using out of water. With glass it is not an issue. Polycarbonate (Lexan) and vynyl (Perspex) material is similar to other plastics in that they are both poor conductors of heat, and will burn/melt when overheated. Too thick a lens and the heat will not transfer outside fast enough, causing the inside to melt, or as in the factory Maglite Lexan lenses 'brown-out'. It burns your lens permanently a brown opaque colour, like the toilet windows in a cheap night club.

 

[baywatch106]

packhorse, what method of lense sealing do you use? What size oring in front of the lens?

 

[350xfire]

OK, so I've decided to get with a machine shop and see about designing a bezel that will allow for 1/4" lens or for Pack (and the non-USA bunch) 6.35mm... Additionally, I will have the bezel grooved to accept an 1/8" o-ring (3.175mm for Pack)...

Also, design a thicker plug for the barrel to allow the gland to thread without posiibility od stripping the threads. I will also have some custom boro glass cut for this project.

If anyone is interested, I'll get 20-50 sets made. This should make Mag conversions a snap... Kit will have bezel, end cap, o-ring, glass lens.

Have no idea on price yet.

 

[baywatch106]

I would be interested

 

[Klem]

If you want to spend time in the workshop knock yourself out... but as I said, a standard Maglite with 6mm Perspex lens goes to 100Mts and back without leaking.

The only cost and effort needed is replace the switch with a piezo and toggle circuit, the end-cap O ring for a thicker 2.5mm and the other parts get glued together.

Or, if you use a canister, then no piezo, cut past the switch hole and glue. Silastic sealant for the access ports, so it is sealed but can crack it open in a vise if you ever need to (which hopefully you won't).

 

[Packhorse]

How do you get a 6mm lens in a maglite? Mine is abot 3.8-4mm and the bezel only just tightens down fully. Have you machined 2mm off the heads thread?


I simple use the next size up O ring that will fit infront of the lens and around the bezel.

 

[350xfire]

If you want to spend time in the workshop knock yourself out... but as I said, a standard Maglite with 6mm Perspex lens goes to 100Mts and back without leaking.

The only cost and effort needed is replace the switch with a piezo and toggle circuit, the end-cap O ring for a thicker 2.5mm and the other parts get glued together.

Or, if you use a canister, then no piezo, cut past the switch hole and glue. Silastic sealant for the access ports, so it is sealed but can crack it open in a vise if you ever need to (which hopefully you won't).

Thing is I don't want to use plastics for the lens and I want 1/8" o-ring crushed tightly on the lens. I want this thing to look like something that came out of a factory and can be disassembled and repaired easily. I don;t want a hack job that is a pain to work on because everything is glued together.

 

[Flo1]

How do you get a 6mm lens in a maglite? Mine is abot 3.8-4mm and the bezel only just tightens down fully. Have you machined 2mm off the heads thread?

Have a squiz at post #49.. stepped lens..

 

[Klem]

350XFire,
Fair comment, keeping the original access joins as they were meant to be has merit. If your O rings work to the depth you want, and you look after them, not a problem. I'll be interested to see (pickies) and hear how it goes.

Packhorse,
No stepped lens. The full 6mm of lens sits in the bezel and no machining of the threads. The bezel does not screw up as much as narrower lenses and yes, because of that you can't use an O ring. The seal comes from a tube of Silastic being squeezed onto the theads, do the bezel up and wipe off the excess. There's also no O ring in front of the lens. Epoxy putty is pushed into the bezel and the lens then pushed up hard against the lip of the bezel, so you save a little space there. The Perspex comes with protective brown wax paper so the epoxy can't dull the 'clearness' as you push it into place and then leave it compressed in a vise to cure. I cut the disk, put it in the Maglite bezel and run a pencil round from the front. Then carefully cut with a scalpel and remove the paper so the glue can stick (see photo), but the paper protects the lens while you are using messy fingers and vises. Then peel it all off when it is dry.

Here are two maglites with glued lenses; the silver bezel is 4mm glass and the black bezel is 6mm Perspex. You can see the black bezel does not screw up as much, but using Silastic instead of an O ring this is no longer an issue. I've also put some of the epoxy in front of the lens on the black one for a better seal but if you want a cleaner look like the top one just run a knife round and remove the excess. Both are waterproof.

Using Silastic gasket sealer instead of glue allows you to open the bezel from time to time for servicing. I've done this a couple of times. The tedious part comes with completely removing all the old cured bits out of the threads for re-sealing. A wire brush does the trick here. Takes about 20 minutes, so you wouldn't want to be doing this every dive.

 

[Flo1]

Packhorse,
No stepped lens. The full 6mm of lens sits in the bezel and no machining of the threads....

My mistake.. I stand corrected..

 

[350xfire]

Klem, what kind of circuit do you have that can take the piezo switch signal? How does Silastic differ from silicone?
Thanks for sharing your project...

 

[Klem]

Flo1,
I agree with you... A stepped lens would also work. By having some of the lens forward of the bezel lip you reduce the gap between the bezel and head when done up. You could use a thick lens and still have a working O ring on the Maglite head (if you prefer using O rings). And as Packhorse rightly said, machining off some of the head thread also does the same thing.

If however you are happy to do away with the O ring and don't want to machine steps in a lens and/or machine threads off the head then you are mandated to use sealant with lenses over about 3.5mm in thickness.

350Xfire,
Yes, good question...my understanding is they are the same. Silastic is the brand name for a silicone-based sealant. I see in the auto shop there are other manufacturer brands that all do the same thing; liquid gaskets that cure. Silastic was the cheapest!

Technically it's not a glue, or at least a very weak one, so the strength of the join comes from the threads on the Maglite (or the bolts holding a car engine together). That's fine for a Maglite as we don't want glue, only waterproofing; so you can re-open it once or twice in the torches lifetime.

The toggle circuit for the piezo is below.

Some notes;
-Costs around $10 in parts and an hour of soldering.
-The circuit chews a few milliamps so you need to be mindful of this (it will slowly deplete connected batteries over a few days).
-I left longer legs and folded the FET at right angles to save space in the Maglites.
-Different types of FET will work, obviously you need to check their ratings, but whatever you choose I would recommend using a 'Logic' FET, so it's either completely off, or completely on.
-The capacitor across the piezo legs is not mandatory...it just stops it from turning on every time you connect power (more helpful in a HID than an LED torch).

 

[MikeAusC]

CMOS 555 for Piezo Switch

"The circuit chews a few milliamps "

Klem - if you use a 7555, the CMOS version of the 555, the standby current will be much less. All other components should work unchanged.

Where do you get Piezo switches ?

 

[Klem]

Mike,

Thanks for the tip...so no confusion, the circuit uses a 556, not a 555 (see photo). Is there an equivalent to the 556 in CMOS?

As for the piezo, I live in Perth, so use either RS Components or buy online from Farnells in Sydney. RS is selling their Schurter piezo's pretty cheap at the moment (double the price for the same switch as Farnells).
http://australia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4561852

 

[Umibuta]

Klem.

I think the Cmos equivalent for the 556 is TS556. This is the CMOS 556 I am using now.

 

[Klem]

OK, will give it a go on the next build
Thanks