# Metal experts: I asked for copper, I think I got brass...



## minisystem (Jun 5, 2012)

I've been getting heat sinks machined for LEDs. I've had several designs made by one machinist where I specified C101 or C110 copper. These alloys are supposed to be >99.9% pure copper and they look and feel like copper: orange-reddish in colour, brown oxidization - just like a penny. I recently had a new machinist make a heat sink where I specified C101 or C110 copper but got back a heat sink that really looks like its made of of brass or some other yellow copper alloy. It is yellow gold and doesn't have the same feel, smell, sound of the copper heat sinks I've had made in the past. The machinist says he ordered the material I specified specially from the metal supplier. Here's a picture:







The new heat sink is on the left, the old one, which I know is C101 or C110 copper, is on the right.

Can someone tell me I'm not crazy? Or are there slight variations in pure copper stock that would give them a yellow gold colour? I'm baffled, but don't have enough experience to say definitively that the new heat sink is brass.


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## derfyled (Jun 5, 2012)

Based on the color, I would also tend to say it is brass. Brass is an alloy of copper and zinc. The more zinc there is, the more yellow it will be. Copper is a softer metal than brass, you could maybe try to scratch the copper heatsink with a knife and then try on the suspected brass one, you might be able to feel the difference.


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## Tofty (Jun 5, 2012)

It can't be pure copper, it must be an alloy.

If you know the heatsinks volume and mass you should be able to work out what the material density is.

Brass is 8.47 g/cm qubed
Copper is 8.94 g/cm qubed

(it would be easiest if the machinist did this with the stock round bar)


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## precisionworks (Jun 5, 2012)

> The machinist says he ordered the material I specified specially from the metal supplier.


All reputable metals suppliers (even those on eBay) will supply a cert upon request. Have him contact the supplier & get a cert - that is the only certain way to know what he got.


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## nfetterly (Jun 5, 2012)

precisionworks said:


> All reputable metals suppliers (even those on eBay) will supply a cert upon request. Have him contact the supplier & get a cert - that is the only certain way to know what he got.



We had an 11" shaft shear at work 2 years ago - sub-supplier hadn't heat treated it. Just saying mistakes happen along the way. Damned if I cannot find the photo - it was pretty impressive.


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## minisystem (Jun 5, 2012)

precisionworks said:


> All reputable metals suppliers (even those on eBay) will supply a cert upon request. Have him contact the supplier & get a cert - that is the only certain way to know what he got.



Yes, good point. He did say that if I was sure it wasn't pure copper that he'd contact the supplier. I convinced there was a mistake now and the wrong material was used.


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## unterhausen (Jun 6, 2012)

I've never machined copper, doesn't it machine totally differently than brass?


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## StrikerDown (Jun 6, 2012)

unterhausen said:


> I've never machined copper, doesn't it machine totally differently than brass?



Yup, Copper seems gummy by comparison.


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## Justin Case (Jun 6, 2012)

Tofty said:


> It can't be pure copper, it must be an alloy.
> 
> If you know the heatsinks volume and mass you should be able to work out what the material density is.
> 
> ...



The Archimedes method is an easy way to do this.


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## minisystem (Jun 6, 2012)

Alright, well it turns out *precisionworks *had the best advice: the supplier admitted to substituting brass for the C101/C110 that was specified on the order, which is pretty shoddy. Needless to say, the machinist expressed his annoyance about the substitution.


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## will (Jun 7, 2012)

minisystem said:


> Needless to say, the machinist expressed his annoyance about the substitution.




Umm - I would think that most machinists would be able to tell the difference between copper and brass. They machine differently, they look different....


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## precisionworks (Jun 7, 2012)

> the supplier admitted to substituting brass for the C101/C110 that was specified on the order


At least there's any easy way to make this right. The supplier ships out C101 or C110 at no charge for material or shipping. And the supplier pays for the cost to machine a second part. They made the mistake & this gives them the opportunity to fix it.


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## eebowler (Jun 7, 2012)

I think it's a bit sad that the machinist didn't realize he wasn't working with copper.


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## minisystem (Jun 7, 2012)

Yes, I agree it would've been nice if the machinist had known that they were machining brass when it was supposed to be copper. I was dealing with the manager, so it's possible the actual machinist that did the job was handed the files and the bar stock that was ordered and just did it, assuming he was given the right material. Anyway, they're getting the correct material and will make it again.

Thanks for telling me I'm not crazy!


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## fyrstormer (Jun 7, 2012)

Is there any chance the copper was ChemKoted? That kinda looks like the color of ChemKote.

The only way to be absolutely sure is to measure the density of the item. Measure its weight, then fill a glass completely full of water and carefully put the item into the water. Catch the spillage and measure its volume. Divide the weight by the volume and check online to see if it's closer to the density of copper or brass.


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## precisionworks (Jun 20, 2012)

Just slightly OT ...

I wanted to make a 5# brass hammer & needed roughly 2" diameter x 5" long. Called my friend who has a great scrap pile & he had a 10" piece that I could buy half of. Warned me that this was "full hard" (H04) and wasn't easy to work. Clamped the rod in the band saw & expected the new blade to slice right through ... and five minutes later it finally finished cutting 

Planning to add a Ti-6-4 handle & maybe a few trits


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## PEU (Jun 20, 2012)

trits for a hammer? :thinking:


Pablo


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## darkzero (Jun 20, 2012)

PEU said:


> trits for a hammer? :thinking:
> 
> 
> Pablo



So he can work in the dark.


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## Th232 (Jun 20, 2012)

I'm wondering more about how much shock absorption you'll need for the trits to be honest.

That said a brass/Ti hammer would look plenty cool.


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## darkzero (Jun 21, 2012)

Th232 said:


> I'm wondering more about how much shock absorption you'll need for the trits to be honest.
> 
> That said a brass/Ti hammer would look plenty cool.



I think they'll hold up if done right, especially in the handle. I have one of Pablo's trit bezels on a light I use for work. While it doesn't nearly get exposed to as much impact as a hammer would, I've banged & dropped it plenty of times without break a trit or falling out. But then again I have replaced broken trits a number of times on Pablo's bezels for people.

Ever since I made the brass/alumn hammer in shop class, I've always wanted to make a fully Ti hammer. Nothing large though & of course I wouldn't want to use it where I could start fires. The risk of lathe fires is bad enough. 

Now those Marsh Ti War Hammers & Ball Peen Hammers are badd ***! I would love to have a few of them.


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## PEU (Jun 21, 2012)

darkzero said:


> So he can work in the dark.



In that case I would put trits at my finger nails 


Pablo


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## precisionworks (Jun 21, 2012)

IMO the coolest way to make the handle is to bore out the end for 1x18650 & fit a titanium twisty head on the end. But a titanium hammer-light might not be the most practical thing in the world. Either a belt sheath or a backpack would be needed for EDC. That said, you'd be ready for any project that needed a little extra persuasion 

I may drill & bore out the end of the handle to shift the center of balance forward. IMO trits would have a long life as long as they are located far from the brass head.


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