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ScubaLawyer
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First Name: Mark
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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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Fibonacci
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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
'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling

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ScubaLawyer
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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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Fibonacci
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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/
'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling

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ScubaLawyer
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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

Vancetp
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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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