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ScubaLawyer
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Re: Question on reproduction silicone diaphragms

Sun Oct 07, 2018 7:24 pm

Hi Phil,

A mold of a cast from a mold just compounds any imperfections. 

The exhaust diaphragm does rest with some slight pressure against the rim of the exhaust horn. When you exhale, the diaphragm lifts just enough to allow air to flow over the lip of the horn and escape. My silicone casts seem to seal a whole lot better than the original diaphragm. It appears the silicone has greater elasticity memory than the original diaphragm, seats better, and pops back into place more readily after the air is exhausted. You may be correct that I have nothing to worry about but the slickness of the silicone (at least the batch I currently made up) just concerns me that one good hard exhalation might pop the flange on the diaphragm out from under whatever is used as a retainer. A good glue might prevent that but i would like to have some redundancy in holding power. I think I'm on to a good thing here but I got a bunch more 'spiramentin to do.

All suggestions welcomed.

Mark.
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

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Re: Question on reproduction silicone diaphragms

Sun Oct 07, 2018 9:17 pm

Looks like you are having a lot of fun... but I can't help but think you are taking the hard path if you want to do limited production runs of these diaphragms.

If you can get a NOS diaphragm (making sure it hasn't shrunk over the years!) and either measure it carefully or get it 3D scanned to generate a 3D CAD model you can use relatively low cost soft tooling and get them produced by injection moulding via a rapid prototyping (RP) company.

Xometry is an example of the type of company I mean... I have no connection to them but their website illustrates the range of RP services available.
They have just added Injection Moulding:
https://www.xometry.com/injection-moldi ... f1EALw_wcB
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Re: Question on reproduction silicone diaphragms

Sun Oct 07, 2018 11:18 pm

Fibonacci wrote:
Sun Oct 07, 2018 9:17 pm
Looks like you are having a lot of fun... but I can't help but think you are taking the hard path if you want to do limited production runs of these diaphragms.

If you can get a NOS diaphragm (making sure it hasn't shrunk over the years!) and either measure it carefully or get it 3D scanned to generate a 3D CAD model you can use relatively low cost soft tooling and get them produced by injection moulding via a rapid prototyping (RP) company.

Xometry is an example of the type of company I mean... I have no connection to them but their website illustrates the range of RP services available.
They have just added Injection Moulding:
https://www.xometry.com/injection-moldi ... f1EALw_wcB
3D printing a prototype and Injection molding likely would be the easiest route for a production run. However, I have zero interest in producing any for commercial sale. Plus, I'm cheap. In fact, I will be very happy to make one or two for myself and maybe a couple of more for a few friends. Plus, I'm a dinosaur. I still shoot black and white film with (gasp) chemical developing. I did look into the possibility of 3D printing a exhaust diaphragm but the material used for printing just didn't seem right for this application. No worries, all good. Keep the ideas comming!
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

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Re: Question on reproduction silicone diaphragms

Mon Oct 08, 2018 12:01 am

Fair enough :D
But there are now a range of silicone rubbers available for direct 3D printing, a process which lends itself to 1-10 units

https://www.aceo3d.com/3d-printing/
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Re: Question on reproduction silicone diaphragms

Mon Oct 08, 2018 12:46 am

Fibonacci wrote:
Mon Oct 08, 2018 12:01 am
Fair enough :D
But there are now a range of silicone rubbers available for direct 3D printing, a process which lends itself to 1-10 units

https://www.aceo3d.com/3d-printing/
That looks really interesting. Thanks for the info. I've already invested in the "analog" version of this project but I'll definitely keep it in mind for the future. Mark
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

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Re: Question on reproduction silicone diaphragms

Wed Oct 10, 2018 1:39 am

ScubaLawyer wrote:
Sun Oct 07, 2018 7:24 pm

The exhaust diaphragm does rest with some slight pressure against the rim of the exhaust horn. When you exhale, the diaphragm lifts just enough to allow air to flow over the lip of the horn and escape.
Interesting. The third "rubber band" valve some Scubas had was added to allow exhaust to escape from extra drillings in the event the exhaust diaphragm stuck to the horn and prevented or restricted exhaust from escaping the end of the horn. They must have experienced this sticking (or had nightmares about it) for them to go to the extra trouble of adding this feature.

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Re: Question on reproduction silicone diaphragms

Mon Jan 20, 2020 2:22 pm

Bumping this thread for an update from Mark.
A sincere THANK YOU to all at VDH who make this wonderful resource available and to all the thoughtful contributors.

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Re: Question on reproduction silicone diaphragms

Mon Jan 20, 2020 3:13 pm

couv wrote:
Mon Jan 20, 2020 2:22 pm
Bumping this thread for an update from Mark.
I got sidetracked with repairs to my house after last winter's storms. I'm currently engaged in massive trial prep activities on a case and just haven't gotten back to it. I do intend to do so but real life has intruded into my play time. I'll be sure and update once I come up for air (so to speak) :)
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Re: Question on reproduction silicone diaphragms

Mon Jun 22, 2020 2:02 pm

In my continuing efforts to duplicate a HW SCUBA exhaust diaphragm, I took two new approaches. The first approach had me stretching pantyhose over the exhaust orifice, holding it in place with an o-ring, and mixing a silicone polymer with a shore hardness of about 40.

My first attempt failed miserably because the o-ring prevented the silicone from coating the sides far enough down to make a sealing surface against the side of the exhaust portal. However, the finished material was super strong.

Image
Image

My second attempt involved me going back to my original mold, using the same silicone mixture, but laying pantyhose material inside the mold. The results were terrific. The new diaphragm is a duplicate of the original and the sides are plenty sturdy to hold the clamp and not tear.

Image
Image
Image

Not so fast, however. The added thickness of the pantyhose, while making the nylon impregnated silicone very sturdy, made the diaphragm too thick along the top edge to properly seat down on the metal exhaust flange (lip). The result is that the sides do not extend down far enough for the clamp top secure it. So it is back to the drawing board. Going to try a thinner more sheer nylon next time. Fingers crossed!

Mark
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

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Re: Question on reproduction silicone diaphragms

Mon Jun 22, 2020 3:18 pm

Good to see you are trying again. That looks like Industrial Strength pantyhose, so I think you are on the right track using the shear leg material. That's what I have been using with good results. It gives the silicone something to stick to and helps keep the shape while still being soft and stretchy. The thin material shapes to the mold and regulator contours easier too. At least that works for me.

In an odd coincidence, I happened to be experimenting on the same item today! "Great Minds...." :D
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Re: Question on reproduction silicone diaphragms

Mon Jun 22, 2020 3:30 pm

antique diver wrote:
Mon Jun 22, 2020 3:18 pm
Good to see you are trying again. That looks like Industrial Strength pantyhose, so I think you are on the right track using the shear leg material. That's what I have been using with good results. It gives the silicone something to stick to and helps keep the shape while still being soft and stretchy. The thin material shapes to the mold and regulator contours easier too. At least that works for me.

In an odd coincidence, I happened to be experimenting on the same item today! "Great Minds...." :D


In all gratitude to Bill, my approach is entirely his idea so I do not take any credit! 8)
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

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Re: Question on reproduction silicone diaphragms

Wed Jun 24, 2020 5:38 pm

I do believe I done did it!

1. Laid the thicker pantyhose material over the exhaust flange.

2. Cinched a thin zip tie around where the wire clamp would normally go.

3. Painted on silicone (Shore Hardness of 40).

4. Let dry and removed the zip tie.

The secret was using the zip tie to hold the fabric against the exhaust flange. My previous experiments already showed the nylon impregnated silicone was strong enough to hold up to clamping. The problem was that with the nylon in place, there was nothing to hold it against the curve of the flange when the silicone was applied so (1) it would not seal, and (2) the outer surface to be clamped was not flat. I tried an o-ring to hold the material next to the flange but that only held it in one small line around the curve. The flat zip tie solved that problem. An now, the big reveal:

Image
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Re: Question on reproduction silicone diaphragms

Wed Jun 24, 2020 7:23 pm

That really looks good Mark, and I think it shows sign of some hope. I'm wondering if using your procedure over the form I made instead of inside the reg would work and allow more room for zip tying the fabric down further so it could be brushed further down, and then be trimmed to the desired length after removing the new diaphragm from the form. Just wondering. I think this issue is definitely getting close to being resolved. :D
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Re: Question on reproduction silicone diaphragms

Wed Jun 24, 2020 7:26 pm

Great job! I'm glad you kept after it instead of giving up.
I ran into problems with the one I made, and seems to be at least in part due to the #10 hardness of the silicone mix I used. It is way too soft to hold its position. Looks like I will need to find a way to thicken it or order some heavier stock.

What did you use to modify the hardness? I don't know much about this stuff since I didn't purchase it. It is some left-over from Jerry M's stash, and surprisingly cures properly. It's just too soft for this application, and it turned out way too soft for the Trieste diaphragm I was attempting.
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Re: Question on reproduction silicone diaphragms

Wed Jun 24, 2020 7:30 pm

Vintagediver wrote:
Wed Jun 24, 2020 7:23 pm
That really looks good Mark, and I think it shows sign of some hope. I'm wondering if using your procedure over the form I made instead of inside the reg would work and allow more room for zip tying the fabric down further so it could be brushed further down, and then be trimmed to the desired length after removing the new diaphragm from the form. Just wondering. I think this issue is definitely getting close to being resolved. :D
I like your idea of making a form with extra room to work on the skirt! I'm going to use your idea for my next attempt at that item. It's what I've been doing on demand regulator diaphragms, but I thought I would save time by just using the reg body this time... I was wrong.

Thanks for the info!
The older I get the better I was.

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