Materials for DIY capsule

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saxtim

Well-known member
Joined
Jun 4, 2004
Messages
88
Location
Melbourne, Australia
I've finished drilling and assembling my first attmept at the capsule described in the Debenham article . (Pictures soon to follow). I'm now ready for attacking the harder part of sourcing diaphragm material etc.

The article describes cutting away material from the brass part of the capsule, but I think it will be easier to make a separate spacer from mylar. Any suggestions what a good thickness would be? Grafixarts have a .001 gauge (24 micron) material - would this be ok?
(http://www.grafixarts.com/dura-lar.htm)

The biggest headache I have is trying to find the metallized PET film. Have many people sourced this with success? I'm going to try emailing Sheldahl, but failing that I don't know where else to look. I did find this however:

http://www.modelresearchlabs.com/using_mylar_covering_materials1.htm

They have metalized silver Mylar in .00025 (by my calculations 6 microns). Right thickness, but I'm not sure if this material would be ok - I have no idea if there are other factors that would make one PET film useable and another not? The also have a range of regular mylar in different thicknesses that could be useable.

I'm also experimenting with building a K67 type capsule - Does anyone have the thickness of A. the diaphragm spacers and B. the spacer between the backplates?

tim
 
[quote author="saxtim"]... describes cutting away material from the brass part of the capsule, but I think it will be easier to make a separate spacer from mylar. Any suggestions what a good thickness would be? [/quote]

Tim Campbell measured the spacer in KK67 when we took that apart - I think it was around 35 micron. Definitely much thicker than the membrane, that may have been some 8-12 micron.

Jakob E.
 
Neumann capsules use the diaphragm as an insulator as well - the ring that has no gold on it - so if you're going to build the backplate as Neumann does (out of a single piece of brass instead of the split piece as used in the Debenham capsule) you'll really need the gold evaporated diaphragm. Or you'll need to 'etch' the metalization off of precoated mylar. I was looking at this too, and decided to build a metal evaporator for this purpose.
 
I am searching for metal covered mylar right now.
I just found this Q and A on
http://www.gefell-mics.com/q_and_a.htm#capsules

Q: What is the difference between PE, Mylar and Hostaphan?
A: They are all the same. Polyethylene is a plastic derivative that is robust and tough. Because of it?s strength it can be made very thin. Mylar and Hostaphan are name brands just as Kleenex is a tissue paper.

I hope that I am not the only one that didn't know.

Patina

:shock:
 
[quote author="dale116dot7"]you'll really need the gold evaporated diaphragm. Or you'll need to 'etch' the metalization off of precoated mylar.[/quote]

Are you sure? I think the mylar they sell for model airplanes is only metallized on one side. Even if it isn't, running some FeCl3 on one side should fix it right up.

The website posted above (modelresearchlabs.com) supposedly has it. These guys also seem to have it:

http://www.samsmodels.demon.co.uk/

Peace,
Al.
 
OK, so I just got a reply from Curt at Model Research Labs, regarding the metallized mylar stuff:

One side only, very diffuclt [sic] to do both sides as it has to go thru the machine twice.

So no need to etch anything... But he did say he only has .0005" thickness for sale (that's almost 13µm). I haven't contacted Sams Models in the UK yet....

Is anyone still reading this thread?

Peace,
Al.
 
I contacted Model Research labs around 3 months ago and found out more or less the same thing - the .00025" stuff wasn't in stock and they weren't sure when they'd have it again.

I ended up using aluminium coated mylar from a motor start capacitor as suggested by Tim and Jacob - there's enough in one probably to do 10's, if not 100's of diaphragms.

I did also find this though, you may be interested:

http://www.wes-technik.de/English/foils.htm
 
[quote author="saxtim"]http://www.wes-technik.de/English/foils.htm[/quote]

Sweet, they got 4µ Al coated mylar foil for 4euros/m! Taking a 2 inch square to do each diaphragm, that's about 250 diaphragms per meter! :shock:

How's your capsule coming, Tim?

Peace,
Al.
 
hey guys. i just got a idea. i saw something on tv a while back. people making ultralight model airplanes/gliders. they are only a few inches big, and weigh less than a couple of ounces with a motor. i think they have some sort of film stretched between the supports, so it might be a lead on where to find some really thin material.

just an idea, could possibly turn up for just another source or something. oh well.
:?
 
ahhhhh....i love that. respond to the post without checking the above link out, then go there and its exactly what i was describing. failure at its finest. :cry:
 
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