DIY mic capsule drawing/starting point

[saxtim]

The following picture/drawing is a starting point for my DIY capsule attempts:

http://www.geocities.com/mejafu/miccapsule.jpg

(copy link to new window to open) - If it doesn't let me know, my ISP is being a bit of a pain at the moment and I'm having trouble getting to geocities to confirm it's uploaded correctly.

Anyway, this is, hopefully, a to scale representation of the Neumann KK67 capsule.

I've taken this picture:
http://www.timcampbell.dk/mic/N_KK67_08.JPG

from Tim Campbells site, and then drawn over it to give, what is hopefully, a to scale representation. Now I just need to know the original dimensions of the capsule before I can start.

I've made a couple of assumptions about the capsules construction, Tim C, maybe you could post whether these hold up or not.

I'm assuming that, after viewing the pictures, that the two halves of the capsule are identical, however they are assembled so that one is rotated 45 degrees to the other. (This is how I've drawn it, if you were to rotate the picture on the right 45 degrees counter clockwise it would be the same as the one on the left.) I'm basing that on the various pictures on your site of the capsule deconstruction, and your own clone. Question is, should it be rotated 45 degrees clockwise, or counter clockwise? If you look at this second picture here:

http://www.geocities.com/mejafu/miccapsule2.jpg

This is rotated the orignal capsule counter clockwise, and you can see how it effects where the holes that go all the way through are, when compared to the original picture above where I rotated the one on the right clockwise.


The other assumption I've is that the layout of which holes are drilled right through, and which ones are only half through remains the same on both halves?

Are these correct assumptions?

In order to make the above picture a 1:1 scale picture I simply need to now the diameter of the KK67 capsule - I'm guessing in the 30-36mm range somewhere?

The other information I need is:

1. the depth of the backplate
2. how deep the holes that don't go all the way through are drilled, and if they are all drilled to the same depth?

As I said this is only a start for me. The main thing putting me off diving in at the moment is that I don't have a metal working lathe to machine the parts. Though I'm pretty sure that one of the highschools I teach at has a metal working subject, so hopefully I might find another teacher there that might have access to appropriate tools.

tim

 

[saxtim]

just re uploaded the files - I'd screwed up resolution. hopefully they'll look right now

 

[Marik]

>The following picture/drawing is a starting point for my DIY capsule attempts:

http://www.geocities.com/mejafu/miccapsule.jpg<

In K67 the both halves are identical and look like the pic on the left. On the right, the pic is incorrect.

>Now I just need to know the original dimensions of the capsule before I can start.<

Diameter--33.84mm
Width (thikness)--4.10mm

>I'm assuming that, after viewing the pictures, that the two halves of the capsule are identical, however they are assembled so that one is rotated 45 degrees to the other. (This is how I've drawn it, if you were to rotate the picture on the right 45 degrees counter clockwise it would be the same as the one on the left.) I'm basing that on the various pictures on your site of the capsule deconstruction, and your own clone. Question is, should it be rotated 45 degrees clockwise, or counter clockwise?<

They are rotated clockwise. In K67 there are two plastic pins, which aligns the halves only in one position. However, to me it looks like they could be rotated counterclockwise, as well, with the same effect.


>The other assumption I've is that the layout of which holes are drilled right through, and which ones are only half through remains the same on both halves?<

Once again, both halves are identical (and symmetrical), and the layout on the left pic/first link is right.

 

[saxtim]

Thanks Marik.

I've uploaded another picture with some dimensions. They may not be perfectly accurate but should be pretty close, at least enough to start experimenting. I've got to update the holes around the outer ring where the screws go and make the symetrical, so I've left off the dimensions/diameters for those at the moment.

http://www.geocities.com/mejafu/miccapsuledim.jpg

Some more questions for you, or Tim C or anyone who may be able to answer.

1. I see the plastic posts in you mention Marik that align the backplates in this picture:

http://www.timcampbell.dk/mic/N_KK67_07.JPG

looking from the front from other pictures I can see that these holes don't go all the way through?

2. If you look at my drawing, you'll see that the holes for the screws - there are 3 each at 12, 3, 6 and 9 oclock positions, plus another 4 spaced evenly between them. On the upper left side though, around the 10 to 11 position there is an extra hole. This isn't present on the membrane retaining rings - what is it's purpose?

3. The holes on the backplate, the ones that don't go all the way through, does anyone know what depth they go?

4. I'm looking at the pictures again, and I'm not sure but it appears that the holes have some sort of taper on them. If you look at

http://www.timcampbell.dk/mic/N_KK67_08.JPG
then
http://www.timcampbell.dk/mic/N_KK67_07.JPG

it appears that they are wider on the front and narrow on the back - this may just be an optical illusion?

5. I can't figure out from any of the picture where the electrical connection is made with the backplate? If I understand correctly there has to be a wire from both the front and back diaphragms as well as one from the backplates.

6. In the original KK67, the two backplates are electrically connected by the scews that hold them together yes? How do you connect them electrically when you're using perspex for the outer part of the capsule (where the scews pass through)

7. I'm curious about a dual backplated capsule, like on in the original u87 where the backplates are electically separated. Is it a different design, or is it infact the same capsule? I ask this as with using perspex it would seem easy to keep the backplates separate. This would mean you'd have to make to connections to the backplates though - depending on the answer to no 3, this may not be hard to do?

thanks

tim

 

[adrianh]

Sharing standard CAD files would be usefull here.
Autocad has the biggest market share.
Autocad lite price is not to steep.

OK going out on a limp.
You get a drawing you hand machine it. It works.
You want to make a million of these capsules for your buddies here at the LAB.
If you have it in CAD system like Autocad you go to a
machine shop with CNC equipment they import your drawing into
Ecam and volia the CNC machine can start turning you out capsules as fast
as you can feet it Brass. Well it is a little more involved than that but
the Cad file is woth the time to get it right.
Since finding people to design mechnical stuff are not on every street corner maybe someone here know a mechnical CAD program like the back of their hand. And they could do the drawings.
To point is the software needs to output files that most people can read.
If you are the only person in the world using ZYX cad program then it is not useful.

 

[adrianh]

perki
Had a cad file from someone.
I have not opened it yet.
Ask him he should share?

 

[saxtim]

Sharing standard CAD files would be usefull here.

Yes- my Dad used to lecture at Uni the use of CADKEY (I believe is equivalent to AutoCAD, and I think the can import each others files no?), he has a copy and could show my how to use it. I just did this up on Corel Draw as it's a program I can use.

At the moment I'm only going to use it as a drilling template/basic drawing to get me started, however I do see the use of getting this thing as a CAD file, that way if people wanted to go the machine shop route rather than the hand way they could.

I think the CAD file Perki had was of the U87ai body - at least that's the one I saw. Someone else had posted a CAD drawing of the CK12 capsule in the old DIY capsule thread.

tim

 

[gyraf]

Saxtim,

4 - yes, the holes are tapered, in two steps. Tim C. has the exact measures, but something like 1.5mm from front and 3mm inwards, and then 0.8mm all the way to the back.

Drill the small one first - all way through, then the large diameter ones with a fixed depth stop.

Don't rush the drilling, and use plenty of drilling oil. It's extremely annoying when the small drillbits sticks and break in the brass - they're close to impossible to get out.

Jakob E.

 

[ward]

I have a cad-file for the capsule in the Debenham, Robinson, Stebbings- article.
(And for the U87aibody that's right saxtim)

I can draw out capsules for you guys if you want, that's easy since it's just a bunch of tubes. Just a matter of :guinness: :sam: :guinness: :sam:
I use autocad 14, which is old but probably still compatible with new versions.

Perki (t****t****) = Ward (the lab)

 

[saxtim]

yes, the holes are tapered, in two steps. Tim C. has the exact measures, but something like 1.5mm from front and 3mm inwards, and then 0.8mm all the way to the back.

Thanks, Hopefully Tim C can chime in and give some more exact dimensions. Do the holes that are not entirely drilled through have a taper on them as well, or are they only drilled with the larger diameter?

I think I made an error with the dimensions on the picture I posted, although the scale should be correct - I'm investigating the CAD thing.

If you have it in CAD system like Autocad you go to a
machine shop with CNC equipment they import your drawing into
Ecam and volia the CNC machine can start turning you out capsules as fast
as you can feet it Brass.

I downloaded the software from emachine shop to see how much it would be to machine just the metal part of the backplate (leaving the outer part of the backplate made out of perspex like Tim C has done). It was around $5.50 for 100, though I hadn't included the hole tapers which would push the cost up I'd imagine. Add to that machining the perspex part and the retaing rings, I think you'd run around $20-30 for a run of 50 capsules (remembering that all parts have to be doubled up for one capsule)

I'm still intending to go the hand method, but I thought some people might be interested how much it would cost for CNC machining.

tim

 

[PRR]

An English magazine once published DIY plans for a condensor mike. You might want to see how they did it.

6 Megabyte PDF file, and you will want to keep a copy, so Right/Long-Click here and "Save Target As..." to your machine.

 

[saxtim]

Nearly finished a CAD file for hte KK67 capsule - with guestimated measurements to some extent (see my earlier post). I still hope someone can answer my above questions, but I ahve another one, which is probably most important:

After studying the following picture carefully:
http://www.timcampbell.dk/mic/N_KK67_07.JPG

I think that all the holes on the insides of the two backplates line up with each other - this is not what I first thought, I thought that the patterns where the same, but rotated to each other so that none of them lined up. Looking at the aligning pins though, I can't see any other way it could work, all the holes do infact line up.

There is only 2 holes that don't line up (one on each backplate), which are on the outer ring where the screws hold the capsule together - I have no idea what these are for - see question no 2. I thought maybe it was some sort of venting hole or something, but that doesn't seem to make sense as it would be sealed at ether end presumably by the diaphragm spacer and the backplate spacer.

I'll point it out when I post the CAD pictures - it might be easier to visualise then

tim

 

[scott_humphrey]

[quote author="Tim Campbell"]Dear Tim,
I'd like to also mention here that unlike electronic designs, the work your discussing here is patented. This is why manufacturers designs vary (at least certain dimensions). There's nothing illegal that I know of of making a copy of something you own for your private use. Posting exact dimesions of a capsule for mass production is a whole other situation.[/quote]

I'm not sure how it works in other countries, but I believe that in the USA patents expire after 17 years. The K67 patent should be long expired.

 

[mnats]

[quote author="gyraf"]It's extremely annoying when the small drillbits sticks and break in the brass - they're close to impossible to get out.[/quote]
An old goldsmith's trick - dissolve some alum (aluminum sulfate) in water. Drop the offending piece in. Next morning, the drill bit has dissolved. Sounds implausible but it's true.

Alum is harmless to gold or brass but eats carbon steel. It's used in pickling cucumbers. You eat it when you bite into a Big Mac.

 

[saxtim]

I'd like to also mention here that unlike electronic designs, the work your discussing here is patented. This is why manufacturers designs vary (at least certain dimensions). There's nothing illegal that I know of of making a copy of something you own for your private use. Posting exact dimesions of a capsule for mass production is a whole other situation.

Tim C - I hadn't really thought of that, good point. I'm not going to have exact dimensions, as I've based my layout on a picture, not actual measurements. Still what I might do is post some pictures of the CAD file without dimensions so people can see what I've come up with, then if people are interested further they can PM and I'll send them a file.

I'm on a little tour right now and so I can't contribute until next week.

Cool - I'll hopefully have posted the above mentioned picture by then and maybe you can chime in again with some thoughs to the questions I mentioned above.

tim

 

[saxtim]

Ok, here's a picture of the CAD file I've got going:

www.geocities.com/mejafu/wholecapsule.jpg

(cut and paste all geocities links into a new browser to open)

Its somewhere between Tim C's version and the original KK67 - note I've included the perspex outer rings (red) perspex retaining rings (green) and spacers (yellow)

I think I've managed to answer most of my above questions myself. At first I couldn't figure out how none of the holes lined up when the backplates where placed together (and rotated for correct alignment). After a lot of trying to imagine it, using the CAD program really helped - here is what I've got:

The back of the first backplate:
www.geocities.com/mejafu/backplate1.jpg

(The two red dots are where the alignment pins go)

The back of the second backplated. This is rotated 90 degrees relative to the first one.

www.geocities.com/mejafu/backplate2.jpg

Note that that the alignment pins are a mirror image to first backplate. I'm trying to think of a way to expain why simply, but I can't - basically imagine you have to pick this half up, then flip it over so that it's back can be against the back of the first half. When you flip it over, the pins will line up.

Here's a picture of one backplate and the outer perspex ring:
www.geocities.com/mejafu/backplatecomplete.jpg
(the blue holes don't go all the way through).

The retaining ring also perspex:
www.geocities.com/mejafu/retainingring.jpg

One of the diaphragm spacers:
www.geocities.com/mejafu/diaphragmspacer.jpg

As for the questions I had above:

I think I've figured out the capsule rotation - hopefully someone can check that for me.

The electrical connection to the backplates, and the dual backplate thing - after reading through the original DIY capsule thread again I've got that down too.

Now I still have a couple of design questions (I've got plenty of practical ones, but I'll save them for when I start building).

1. Still wondering about the depth of
a. the holes that don't go all the way through and
b. the depth of the wider diameter part of the holes that go all the way through.

2. With the backplate spacer - should it have a break somewhere along to vent air, or should it be a solid ring? Looking at:
http://www.timcampbell.dk/mic/N_KK67_07.JPG

all the 4 big holes have to go through (as these are for the screws that hold the capsule assembly togehter), what about the other smaller screw holes - I don't think there are holes in the spacer for these?

3. The 4 big holes for the screws that hold the capsule together - I envisage that two go through from one side, and the other two from the other? For example, looking at:
http://www.timcampbell.dk/mic/N_KK67_02.JPG
you can see two holes that appear to have nothing in them - I imagine that these are where the two screws from the other side come through no?

4. The following holes that is circled:

www.geocities.com/mejafu/extrahole.jpg

I know that it appears on the first perspex ring, and not on the retaining ring. Is there a hole for it in the diaphragm spacer as I've drawn? What is this holes purpose anyway? On the spacer between backplates, is there a corresponding hole as well?

 

[saxtim]

Seeing as there were a couple of other threads discussing capsules, I thought I might bump this back towards the top - has anyone got any thoughts on the above questions I posted?

I'd like to get started soonish, but I wanted to get these things sorted to some degree before I dive in.

tim

 

[alk509]

Hey Tim, what ever happened to this?

Peace,
Al.

 

[adrianh]

Great looking work!!!

We need a cad file!
DXF DWG IGS
If we get a real cad file someone here should be able to convert
it so 99% of the people can read it in there CAD program.