# My designs, about to go to machinist - Please comment!



## MrNaz (Jul 5, 2009)

I am about to have a machinist make the parts needed for a flashlight design that I've been working on for a few weeks now. I think I have the design finally ready, and would like comments on it from the experts in CPF. You can see the designs here:

http://static.mrnaz.com/permjunk/divelight.pdf

The light will run on a 3P2S array of 18650 batteries. The LEDs will be an array of 4 Cree R2-WG emitters using Ledil LC1 optics from Cutter arranged in 2P2S, overdriven using a P7 driver from Kaidomain that can deliver 3A. This should give about a 2.5 hour run time, which, given the output of ~1000 lumens, is great.

The switch will be a reed switch, there will be a magnet stuck inside the switch ring (shown on page 4)

What I really need advice on, though, is the body design. The machinist has these drawings and can make the body immediately, however I don't want to go ahead with that and find out that I've made some silly mistake. Here are the specific bits that I would like comments on:


46mm diameter battery tube. Is this too big? It's larger than a D sized Maglite, which is already a big beefy light. I was considering even having a 4P2S array, which would result in an outer diameter for the body/tube of 51mm, but that's definitely too big for my small hands.
Body o-rings: Is my use of 2.68mm o-rings in a 1.9mm deep groove with a groove width of 3.5mm suitable for a dive light that has to withstand pressure up to 10 bar? I am concerned that the o-rings I've used may be too thin. Can anyone comment on this?
The design of the bezel seal (last page) calls for a compression seal using 2x 2mm o-rings compresssed against the glass's edge with a 25% compression ratio. This design *seems* to be sound to me, but can anyone look it over and ensure that it's OK. There are two o-rings per ingression path on the bezel, so to my eye the design should provide redundancy.
Overall strength of the design. It will be made out of 6061 Al, and I want to know if this design will stand up to the sort of abuse it's likely to get as a dive light rolling around the decks of dive boats and in the trunk of cars amongst scuba tanks.
Overwall waterproofness of the design. This is going to be a dive light, so I need to know how well it will stand up to pressure. Is a 3mm thick polycarbonate lens sufficient for a diameter of 60mm resting on a 2mm lip? Are the o-rings thick enough?
Any other comments are most welcome, I would like as much feedback as I can get before I send this off to the machinist.


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## jeffosborne (Jul 5, 2009)

Hi MrNaz! I am no expert on a design like this, especially the watertight aspects, but I have a thought to share. This light, above water, would be heavy enough to warrant a neck-strap. My Hydra-2 light weighs 1.3 pounds, and needs the strap. Too heavy to put in a pocket, and too big anyway. And underwater, I expect that at least a wrist strap would be good in case you accidently let go of it, so it does not end up in 'the abyss'. So some small loop holes somewhere in the body for attachement of a carry strap is my suggestion. Cheers, Jeff


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## blesbok (Jul 5, 2009)

Hi MrNaz,

I too am working on an LED dive light, but every time the design is 98% complete, I decide to completely change it. One year on, the light is still mostly designed.

Overall your design seems sound and I have just a couple minor comments.

- You have a radius on the bezel, good idea. How about the tail cap too.

- The machined edges where the tail cap and circuit housing are sharp as drawn. Make sure to break these edges or they could (will) slice an o-ring. 

- The o-rings are definitely not "too thin" if used properly. There are plenty of references to check your groove dimensions. Sealing surfaces usually have a roughness called out.

- The double o-ring arrangement for the lens will likely work, but it doesn't sit quite right with me because they are not completely captive. The rings could squirm around a bit when tightening the bezel. Consider adding a step at the end of the circuit housing and an undercut inside the lip of the bezel.

- The lanyard/wrist strap is a great idea. Make sure the machinist knows the "large hole" should not go through the cap, into the housing. 

- If you plan to change batteries in the field, consider making the tail cap thread internal on the body tube. Either way, one part will have external threads, but the tail cap is much lighter and less likely to be damaged when dropped.

Good luck on the build.

Cheers,
Brent


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## A123Powered (Jul 14, 2009)

Will there be some detent on the switch ring? Seems like it could spin freely unless that is the plan. Also, as this is a dive light, maybe a means of gripping the ring with gloves on is necessary?


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## wquiles (Jul 14, 2009)

MrNaz said:


> I am about to have a machinist make the parts needed for a flashlight design that I've been working on for a few weeks now. I think I have the design finally ready, and would like comments on it from the experts in CPF. You can see the designs here:
> 
> http://static.mrnaz.com/permjunk/divelight.pdf
> 
> ...



I like the overall design very much - it looks a lot like the Barbolight diving lights that I have been customizing.

The ONE problem I see in your design, is that you have not specified tolerances in ANY of the dimensions. It is impossible, even for a CNC machine setup, to hit all of those dimenssions precisely, even more so when done by hand. You HAVE to specify tolerances as it is no possible to achieve perfect cuts with the exact values you are using. 

For example, length of the battery tube is listed as 140mm - it probably should be something like 140mm +/- 0.5mm (just an example - you really need to work with your machinist on what he/she can achieve with his/her equipment).

This applies to every single measurement you have. Sometimes you can "afford" a part to be slightly larger, but not smaller, so you would then do like: 140mm +0.5mm/-0mm.

If you ask a moderator to move this on the Machining sub-section, you will see what I mean as we have very experienced machinist that participate actively in that forum.

Best of luck 

Will


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## DM51 (Jul 15, 2009)

Moving to MMM...


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## gadget_lover (Jul 15, 2009)

If the size seems large, I would suggest that you make a mockup from cardboard, wood, clay or whatever materials work for you. Add weight to approximate the weight of the real thing. Then try holding it while wearing gloves, while picking up your other gear, etc.

I'll glance at the PDF after work tonight.

Daniel


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## MrNaz (Jul 15, 2009)

gadget_lover said:


> If the size seems large, I would suggest that you make a mockup from cardboard, wood, clay or whatever materials work for you.



Thanks. I've since found out that it is in fact fine, I've held an object roughly the same diameter and it is easily well within comfortable size bounds, even with my tiny hands.

The design has changed a bit since those were drawn up, but the overall design is more or less the same. Any comments you may have would be much appreciated.


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## meatshieldChris (Jul 15, 2009)

I know you were looking for advice, but can I ask a question too? What kind of reed switch did you find that would handle the currents of a P7 in a form factor that would fit a flashlight? I'm really interested in this method of switching for flashlights.


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## 65535 (Jul 15, 2009)

It's possible to wire a relay or transistor to switch the unit on. A small reed switch could then be used to switch any amount of power into the megawatts.


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## meatshieldChris (Jul 15, 2009)

65535 said:


> It's possible to wire a relay or transistor to switch the unit on. A small reed switch could then be used to switch any amount of power into the megawatts.


oohh yes, that makes sense. What about resistance to impact?


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## 65535 (Jul 15, 2009)

Reed switches are pretty tough aside from over current.


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## gadget_lover (Jul 15, 2009)

They are known to weld themselves shut on occasion if there is a hefty current when the contacts close. There are premium reed switches that have coatings to avoid that problem.

I see your callout for the threads is 1mm pitch, 1mm deep. If you want an ISO thread, the depth is predetermined by the pitch. There is a formula for the ratio of pitch to depth. That may influence some of your dimensions.

If I remember correctly, the depth for a 1 mm pitch is .866mm, but a proper ISO thread cuts off the top 1/8 of the screw's thread (the crest) and 2/8 of the nut's thread.

NIce drafting, BTW.

Daniel


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## darkzero (Jul 15, 2009)

wquiles said:


> The ONE problem I see in your design, is that you have not specified tolerances in ANY of the dimensions. It is impossible, even for a CNC machine setup, to hit all of those dimenssions precisely, even more so when done by hand. You HAVE to specify tolerances as it is no possible to achieve perfect cuts with the exact values you are using.
> 
> For example, length of the battery tube is listed as 140mm - it probably should be something like 140mm +/- 0.5mm (just an example - you really need to work with your machinist on what he/she can achieve with his/her equipment).
> 
> ...


 
Will has a good point there. With some of the local machine shops I've used (non flashlight related), the tighter the tolerances the higher the cost to machine.


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## MrNaz (Jul 15, 2009)

meatshieldChris said:


> I know you were looking for advice, but can I ask a question too? What kind of reed switch did you find that would handle the currents of a P7 in a form factor that would fit a flashlight? I'm really interested in this method of switching for flashlights.


 
I'll be using a reed switch+resistor from the battery to put 5V through the gate of a power MOSFET, through which the main current (about 2.5A) will flow. This ensures that only a trickle of current goes through the reed switch.

Physically, reed switches are pretty tough. I'll be using epoxy to mount it to the inside of the circuit housing, and a magnet embedded in the switch ring to operate it. This is a pretty common switching mechanism, Packhorse does it all the time on his canisters.



darkzero said:


> Will has a good point there. With some of the local machine shops I've used (non flashlight related), the tighter the tolerances the higher the cost to machine.



I've already spoken to a machining shop, they have looked over the designs, made a few changes and we've discussed where the tolerances matter and in which direction. Yes, this is something I knew zero about, and chatting with them was very informative.



gadget_lover said:


> I see your callout for the threads is 1mm pitch, 1mm deep. If you want an ISO thread, the depth is predetermined by the pitch. There is a formula for the ratio of pitch to depth. That may influence some of your dimensions.



Yes, I've since discovered that threads have a standard angle of cut. I was guessing when I did those plans, and the machinist has since suggested a 1.25mm thread which is slightly less than 1mm deep, which is good as it increases the minimum thickness of the walls.

I've also switched from AS-568-1xx standard orings (2.62mm) to metric orings, 2.0mm in cross sectional area. That should be sufficient, all tables I've seen state that given the tolerances that the machining shop is able to do, the orings should stand up to well over the necessary pressure.


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## PEU (Jul 15, 2009)

I see problems with the orings, the lens cover ones will move around, the one at the head meets body has too wide space, it will move and not seal properly.

Download: *Parker oring handbook*. Tons of good advise about how to use them. Oring compression should be around 10-20% you may want to be on the 20% side since this is a dive light. Consider double set of orings per junction.

Will advised you about tolerances, unless you can be next to the machinist while the part is being made, specify them, and always remember:

- its far easier to remove material than puttting it back
- assumption is the mother of all ****ups 




Pablo


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## MrNaz (Jul 17, 2009)

PEU said:


> I see problems with the orings, the lens cover ones will move around, the one at the head meets body has too wide space, it will move and not seal properly.



This has been redesigned to a seat type seal.



PEU said:


> Download: *Parker oring handbook*. Tons of good advise about how to use them. Oring compression should be around 10-20% you may want to be on the 20% side since this is a dive light. Consider double set of orings per junction.



Great resource!

All orings are compressed to 25% give or take a % or two. Is this too much? Must sources say between 10 and 30% is allowable, and I've aimed for the higher end of that bracket. Apparently 40% can be used on a static seal. I've read so many conflicting opinions on this that I don't know if I'm doing the right compression ratio. Is 25% ok?



PEU said:


> Will advised you about tolerances, unless you can be next to the machinist while the part is being made, specify them, and always remember



Addressed. The machinist is keenly aware and has spent a long time with me, and fully understands the needs of the design.

Many thanks for your input!


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## PEU (Jul 17, 2009)

Compression will determine how easy/hard will be to open the unit, I assume its not a twisty, keep in mind pressure may build up inside the unit and make things difficult when you try to open it to replace batts.

Im guessing here, but if its going to be used for recreational diving (less than 130ft) I don't see the need of going much more of 20~25% compression of the (dual) orings.

IMHO, this should be tested before putting the electronics into the unit, go dive with it and get some real experience with the flashlight, if everything goes OK, then assemble.

Good luck!


Pablo


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## gadget_lover (Jul 17, 2009)

Thanks for bringing up the subject of pressure. 

Dive lights tend to be set up as water and air tight....
Batteries tend to outgas.
Add internal pressure to a light that is well sealed and things get interesting. 

You might end up with enough pressure that it's difficult to open. Some batteries outgas hydrogen, and there are reports of tightly sealed flashlights that popped when the tailcaps were removed.

A small one-way valve is often the cure.

Daniel


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## MrNaz (Jul 17, 2009)

gadget_lover said:


> A small one-way valve is often the cure.
> 
> Daniel


We have added a one way valve and a recessed cavity to house it on the tail cap to ensure that if a large pressure does build up, it does not cause an explosion.


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