Help: casting vintage mic

N

nomuse

Sr Member
RPF PREMIUM MEMBER
I've got a rush job for three non-functional prop mics. I also have a (vintage) Shure55 lying around. I could throw it in a box of Oomoo and make a couple of quick pulls from that, but I can't figure out how to keep the silicone from oozing into the grill. I don't want to wreck the mic, either.

My best thought so far is to use something like paint or white glue as a sealant -- something I could rinse out of the grill with warm water (I'm taking the original microphone apart to try to repair the electronics, anyhow, so now problem to dunk the shell in a tank and soak it for a while). The grill is metal, and attached to the shell with either brazing or some sort of industrial epoxy; it is hard to tell, but it isn't going to come out easy.

Any thoughts?


(We're opening next Friday, and I've got no time for carving or 3d modeling to print it -- or even time for a mail-order replica to arrive. Our fall-back is throwing together some found-object fake mics with silver spray paint and hot glue. Which is what we're rehearsing with right now anyhow.)
 
Hmmm, I was thinking you could back it with chavant clay but that would be a real pain to clean out after the fact. Residue could be dissolved with orange oil cleaner but I have no idea what it would do to any finish. White glue is waterproof after it's dry. I'd stay away from it. I wouldn't trust paint either. You could try gobbing on lots of Vaseline behind the grill and jam some shaped Styrofoam or flexible foam behind that. With that thought... a stuffed sock as a backer and vaseline to seal the grill. Then box it and rtv (oomoo).

I have a fairly hi-res model I did of that mic from a 3D print project I did for a client years ago. It's got the client logo on the base so it would need additional modelling to remove. I'd have to dig up the file as well. I think I archived it a long time ago so that's probably a long shot.

I think the vaseline and a backer of some kind would be the most straight forward solution. I've done this before to build a block mould with RTV. So I know it won't react with your silicone. Only thing you'd need to be sure of is that you sealed the grill with enough vaseline to be sure it didn't leak at all.

Cheers!
mattermaker.
 
Last edited:
Check out maskol made by humbrol.

Its a UK product but I'm "shure" you could find an alternative where you are.

It will peel right off after you're finished.

Not sure what you intend to use to make the mold so maybe brush some petroleum jelly to stop the mold material sticking to it.
 
I would use Saran-wrap on the inside with a ball of clay that presses onto the saran-wrap. The Saran wrap stops the silicone to get into the mic and stops the clay from sticking into the grill.
 
Contec said:
I would use Saran-wrap on the inside with a ball of clay that presses onto the saran-wrap. The Saran wrap stops the silicone to get into the mic and stops the clay from sticking into the grill.
Click to expand...

Great idea, I have no idea why I didn't think of that!!

mm.
 
About two years ago I did a custom American Idol mic for FOX. The outer ring is a slice from a large (8") PVC pipe coupling. The springs came from the hardware section at lowes, along with some common eye screws. The mic body is a short section of PVC pipe, with the grill from a cheap harmonica mic. I used silver rattle can spray paint on everything but the grills and mic "can" , which got nickel paint- also from a rattle can. The call letters were cut with our CNC router. The stem is a piece of metal conduit (emt). We welded a nut to a washer, then welded that to the inside of the conduit. We put a stove bolt through the outer ring and just screwed on our conduit handle. Total parts cost was about $100. It shipped 30 hours after we got the call, so it was a quick build. Having done this one, it would probably take about 5 hours to make one (now that we figured out the design). It's a different style than the shure55 so I'm not sure if you can use any of this for your current piece, but I hope it helps. BTW FOX paid 3k for the mic, so trashing brand new harmonica mics just for the grills was an easy decision for time saved.
 

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nomuse said:
I've got a rush job for three non-functional prop mics. I also have a (vintage) Shure55 lying around. I could throw it in a box of Oomoo and make a couple of quick pulls from that, but I can't figure out how to keep the silicone from oozing into the grill. I don't want to wreck the mic, either.

My best thought so far is to use something like paint or white glue as a sealant -- something I could rinse out of the grill with warm water (I'm taking the original microphone apart to try to repair the electronics, anyhow, so now problem to dunk the shell in a tank and soak it for a while). The grill is metal, and attached to the shell with either brazing or some sort of industrial epoxy; it is hard to tell, but it isn't going to come out easy.

Any thoughts?


(We're opening next Friday, and I've got no time for carving or 3d modeling to print it -- or even time for a mail-order replica to arrive. Our fall-back is throwing together some found-object fake mics with silver spray paint and hot glue. Which is what we're rehearsing with right now anyhow.)
Click to expand...

How did this turn out?
 
Pippspriller said:
How did this turn out?
Click to expand...

Well, the disassembled 55 is still on my workbench. We ended up with three cheap dynamics (the kind they throw in as a bonus when you buy an "On Stage" brand mic stand at Guitar Center). Which was totally fine as the scene was dark and full of hazer anyhow.

I have "Poppins," "Hairspray," "Charlie Brown," and "Fiddler" coming up and none of them will need a prop mic. Well, "Fiddler" might -- that director is famous for his creative setting. We did "Narnia" as Russian Expressionist, and "Pirates of Penzance" as diesel-punk.

Still a worthwhile project, but I'm prioritizing something else; a theatrical version of the "Blaster Core" -- trying to make a portable, battery-powered, and remote controllable 10-watt RGB source (or RGBA) for theatrical props and lighting effects. Deep in the literature now on boost converters and constant-current LED drivers. Fortunately, the Arduino-compatible sequencer and the XBee wireless link are all things I've used before.
 
I think the laser will be constantly on but the sound trigger idea is freakin brilliant. I'm trying to find a relatively inexpensive laser that has a function that can oscillate rapidly between two points I can define (width control). All the cheap-ish stage lasers only seem to run preset patterns... I just want to paint a flat plane.
 
Pippspriller said:
. I just want to paint a flat plane.
Click to expand...

Something that does that should be pretty easy to find, I have a thing I picked up at our annual antique radio conference
where we have a "end of swap" auction where stuff that left over that didn't sale in the flea market and other stuff that's donated
to be sold for the club. I think it's made by Ryobi, it's used for laying out things on walls, it makes a wide flat laser beam, don't know
if it's 180 degrees or what, but it's a wide flat beam, you can change it from horiz to vert and has adjustments for leveling,
I think I paid $5 for it :)

73, Ron w4ron
http://radioheaven.homestead.com/
Ron in Radio Heaven.jpg
\
 
Apparently you can find a galvo for under a hundred bucks. Or even cheaper, if you make your own out of a speaker or similar. Or hack a already-built stage laser; pull out the controller (leave the laser driver alone!) and replace with Arduino or similar so you can write your own patterns.

Yeah, my memory is that it was always on, but there was a distinct sound when you broke the beam, which changed when the area broken was larger (aka a whole body instead of just a hand). But I also recall seeing a "scan line" drifting through the sheet of light, which gave it some of that interesting character. If you were actually painting -- aka with a laser mirror -- both the static flat plane and some superimposed relative intensity shifts are both easy to program.


(Still deep in the documentation for my project -- even power MOSFETs can get a little complex if you are trying to do it right. And the constant-current sources with PWM are proving a huge pain for me to work out. Plus I'm too broke this month to have PCBs made or even purchase components).
 
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