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Removing barrel dent on a Schoeps CMC5


MattPadden

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Hi,

My first post here, so a friendly wave to you all.

 

I have a Schoeps CMC5 mic in here for repair just now. Its main issue is a lack of output (turns out there’s a regulator capacitor gone short) but the bigger issue is a shallow, oblique dent in the barrel that makes extracting the mic’s innards very difficult. Attempting to reinsert the innards looks to be impossible without putting excessive strain on the circuit board, so I need to find a way to ease out the dent. Has anyone tried this, and with any measure of success? I’ve tried running a very tightly shimmed screwdriver handle into the barrel, but no success. I can’t compress or clamp the barrel without risking damage to the exterior finish. Image attached for detail.

 

many thanks,

Matt

 

827A6518-82A7-4118-A79C-DC064E1E7FE6.jpeg

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Way back in college I took a brass instrument repair class. It was just intro/basic stuff but this is the kind of repair we worked on.

 

To remove a dent from a tube, we inserted a mandrel (a solid metal cylindrical rod) slightly smaller than the tube diameter and hammered out the dent with a soft mallet – leather I think.

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You can buy a new barrel. There are two lengths available so be careful to get the correct length. They used to be available for a really reasonable price, but like many things, they've gone up over time.

 

Here in the U.S., Redding Audio is the distributor, and on their Schoeps replacement parts page (https://www.reddingaudiostore.com/replacementparts.html) they only list the 99mm version. Their price for the Gray finish (CMCg) barrel is $66, and for the nickel version is $99 (CMCni). I don't know who the nearest dealer to Glasgow would be.

 

I recall that price being more than twice what I paid for a nickel sleeve -- yep, it's been a good while since I replaced one.

 

 

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I too have a CMC with a dented tube  (purchased used but sounds great) and simply want to make it look less beat up. I cannot extract the guts to pound out several dents because the indents disallow extraction of the guts.

 

This Schoeps tube must be thinner walled than my numerous Sennheiser tubes. They are many years old and no dents. Of course i dont drop them but i have had boom ops smack them on props from time to time.

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5 hours ago, Shastapete said:

Way back in college I took a brass instrument repair class. It was just intro/basic stuff but this is the kind of repair we worked on.

 

To remove a dent from a tube, we inserted a mandrel (a solid metal cylindrical rod) slightly smaller than the tube diameter and hammered out the dent with a soft mallet – leather I think.

This is what I was trying with the shimmed screwdriver handle. I’ll try thickening the shim slightly; I’m using drinks can aluminium so another turn of the stuff may work. A replacement barrel is out of reach financially so I will keep working on it. 

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Matt, please go cautiously. You can dent it in the other direction and make things worse. Normally, dent work like this is done with a backup on the opposite side of the mandrel to prevent mis-shaping. As said, ideally, the mandrel has a slightly smaller radius than the inside diameter. On the outside, there should be a backup mandrel with a soft protective layer (leather) to help keep the shape.

 

I like to fabricate. I have a mill and a lathe. I would be more than entertained to make the mandrel and backing mandrel for you at no charge. Hey, I have time on my hands and I need to stay busy. So don't hesitate. If interested, I need a fairly precise measurement of the inside diameter and outside diameter.

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21 hours ago, Paul F said:

Matt, please go cautiously. You can dent it in the other direction and make things worse. Normally, dent work like this is done with a backup on the opposite side of the mandrel to prevent mis-shaping. As said, ideally, the mandrel has a slightly smaller radius than the inside diameter. On the outside, there should be a backup mandrel with a soft protective layer (leather) to help keep the shape.

 

I like to fabricate. I have a mill and a lathe. I would be more than entertained to make the mandrel and backing mandrel for you at no charge. Hey, I have time on my hands and I need to stay busy. So don't hesitate. If interested, I need a fairly precise measurement of the inside diameter and outside diameter.

 

Paul F, that's extremely gracious; thank you for the offer and I understand totally the risks you describe. The only potential hurdle is that I'm in Glasgow, UK; naturally I'd be happy to pay the shipping cost of course.

 

Let me establish the inside and outside diameters and I'll get back to you.

 

 

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FWIW, Redding Audio is only selling the 99mm Schoeps barrels these days, the 96MM (?) are all sold and NLA.  They will work on the older Schoeps but you'll need to remove the little S/N ring to make them fit.

 

https://www.reddingaudiostore.com/catalog/item/8157888/8838860.htm

 

Also possible that Jerry Bruck who owns Posthorn Recordings might have some 96mm sleeve in his collection although I am not sure how current his inventory is.  He is getting along in years and may be out of the Schoeps game by now.  The price list on the web says 2009. :(

 

D.

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Lol, i thought about the old dry ice trick to contract the metal and raise the dented areas on my tube like the hail damage guys do on automobiles, for about 2 seconds. The problem is I can't extract the guts because of the dents. Repeated applications of heat and dry ice would not be good on the electronics.

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On 7/13/2020 at 10:39 AM, PMC said:

This Schoeps tube must be thinner walled than my numerous Sennheiser tubes.

 

I'm curious about this. I measured an Octava and it has a 2mm wall thickness. I tried a test on an aluminum and a copper tube that both have the same wall thickness. I placed a needle nose pliers on the tube and struck it with a hammer pretty hard,  I can only scratch the aluminum. I can make a small dent in the copper (nothing like shown in Matt's picture). Even with the small dent, the tube is already out of round. It now has a slight oval shape.

 

 

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5 hours ago, tourtelot said:

FWIW, Redding Audio is only selling the 99mm Schoeps barrels these days, the 96MM (?) are all sold and NLA.  They will work on the older Schoeps but you'll need to remove the little S/N ring to make them fit.

 

https://www.reddingaudiostore.com/catalog/item/8157888/8838860.htm

 

Also possible that Jerry Bruck who owns Posthorn Recordings might have some 96mm sleeve in his collection although I am not sure how current his inventory is.  He is getting along in years and may be out of the Schoeps game by now.  The price list on the web says 2009. :(

 

D.

noyz boyz in NL has 96mm tubes on their website: https://www.noyzboyz.nl/en/sleeve-cmc-96mm.html

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14 hours ago, Paul F said:

Very good. Also, please tell me the tube wall thickness. I want to try to duplicate the problem and test the mandrel.

 

OK Paul F, here are the dimensions. I used a digital caliper; the measurements below are an average in each case from three readings taken around the circumference:

 

External barrel diameter 20.04mm

Internal diameter 18.92mm

Tube wall thickness 0.50mm

 

As far as I can establish the dent itself is around 0.5mm depth.

Note that the barrel isn't clear all the way through; there is a reinforcing ring in the last 4mm of the threaded (capsule) end which reduces the inner diameter slightly. However the dent is not in this region, so getting a mandrel in shouldn't be an issue.

 

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16 hours ago, MattPadden said:

 

On 7/13/2020 at 10:39 AM, PMC said:

 

 

I made a .5 mm walled tube out of copper and one out of aluminum (I don't have brass). I struck a flat putty knife edge with a hammer on the tube. It required quite a whack to get it to dent the same amount. It also distorted the tube into something of a oval shape. I'm thinking your tube is also distorted.

 

The sketch is what I propose. The internal mandrel will be made of steel. The outer mandrel will be made of aluminum and lined with moleskin (is moleskin understood in the UK? It's a soft, thick fabric with adhesive on one side to be used on foot sores). The internal mandrel will have a slightly smaller radius than the I.D.. It will be ground down on the sides (dotted line) to make it easier to fit in the tube and get past any distortion of the tube. The end will be filed and sanded down (not shown) to provide a soft radius to prevent a sharp edge from being made inside the tube.

To keep the mandrel flat, there are two support mandrels. One is under the tube. The other is on the far end of the internal mandrel. I have them drawn backwards. The longer outer mandrel should be under the tube. The shorter mandrel will .5 mm taller to compensate for not having a tube under the far end of the mandrel. Once set up, you strike the flat surface of the mandrel with a hammer.

 

Do you see any issues with this? I will test it to see if it does any good. Having seen how much force it took to make that dent, I'm hesitant about success.

20200715_163244.jpg

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4 hours ago, Paul F said:

 

I made a .5 mm walled tube out of copper and one out of aluminum (I don't have brass). I struck a flat putty knife edge with a hammer on the tube. It required quite a whack to get it to dent the same amount. It also distorted the tube into something of a oval shape. I'm thinking your tube is also distorted.

 

The sketch is what I propose. The internal mandrel will be made of steel. The outer mandrel will be made of aluminum and lined with moleskin (is moleskin understood in the UK? It's a soft, thick fabric with adhesive on one side to be used on foot sores). The internal mandrel will have a slightly smaller radius than the I.D.. It will be ground down on the sides (dotted line) to make it easier to fit in the tube and get past any distortion of the tube. The end will be filed and sanded down (not shown) to provide a soft radius to prevent a sharp edge from being made inside the tube.

To keep the mandrel flat, there are two support mandrels. One is under the tube. The other is on the far end of the internal mandrel. I have them drawn backwards. The longer outer mandrel should be under the tube. The shorter mandrel will .5 mm taller to compensate for not having a tube under the far end of the mandrel. Once set up, you strike the flat surface of the mandrel with a hammer.

 

Do you see any issues with this? I will test it to see if it does any good. Having seen how much force it took to make that dent, I'm hesitant about success.

20200715_163244.jpg


Paul F, this seems clear. Moleskin over here is the same as over your way too, so all good. Let me know how your tests go. 
 

As a variant on the idea, I had a thought for the inner and outer mandrel to be full rounds (the inner thus a circular peg piece with a tapered end, the outer thus a round hole in a square block). In this way the outer could be held in a vice, the mic barrel resting in the hole, and the inner peg hammered carefully in to bring out the dent. I guess the issue would be how the outer in this arrangement holds the barrel snugly enough. 
 

 

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Success! I managed to reassemble the CMC5 with some extremely careful compression around the shoulders of the dent while I 'milked' the capsule mount past. Slow and steady work, but all is now well and the mic is a happy mic. The dent is still there of course, but I'm tempted not to tempt fate here.

 

Paul F, if you've already made the mandrel then I will with gratitude cover shipping costs to the UK and it can lie in wait for future 20mm barrel dents.

 

Thanks all for your advice and cautions; all were valuable.

 

 

J323 mic reassembled.JPG

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