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Copper Polishing.

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Copper Polishing.

Unread postAuthor: Mpeddlesden » Tue Jul 13, 2010 4:29 am

Hi, im building a 400+psi QEV bolt action copper rifle, with a oak stock.
4x32 scope. ammunition Holder, and bi-pod.

The gun it's self is about 60% completed and i just finished polishing the 3/4 copper chamber but the soldered weld's remain and i believe that
"If your not happy with it it's not finished."

So what would be the best way to remover them?
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polishes 3/4 chamber with ugly weld's.
Sidebysideview.jpg
3/4 chamber with 1/2 barrel running alone length.
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Unread postAuthor: Technician1002 » Tue Jul 13, 2010 5:04 am

The light coating of solder and coper oxide from heating can be easly removed by using 0000 steel wool. After the surface is clean, then proceed to polish with your favorite metal polish. A buffing wheel and jewler's rouge works well and so does Brasso.

You can pre polish with 600 to 1200 grit sandpaper to remove the scratched appearance you already have and polish to a mirror finish.

Initial sanding produces a scratched appearance.
Image

When you move to fine sandpaper, the larger scratches vanish and the metal starts to get a fine shine that can be finished with polish. The pipe below was only sanded. It is not polished yet. The smooth finish is for a valve. The pipe on the left is what the pipe looked like before I started.

Image

Copper can be polished to a fine shine.
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Unread postAuthor: Crna Legija » Tue Jul 13, 2010 5:49 am

maybe you could use the stuff that you clean the weld marks off stainless steel, i think its called pickle juice. its a mix of nitric and hydrofluoric acid.
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Unread postAuthor: inonickname » Tue Jul 13, 2010 8:07 am

-_- wrote:maybe you could use the stuff that you clean the weld marks off stainless steel, i think its called pickle juice. its a mix of nitric and hydrofluoric acid.


Hydroflouric acid? Don't. Just don't.

Just use fine sandpaper (wet + dry), then finish up with a foam scotch pad or steel wool.

Unless you know what you're doing, don't use any chemical solution. Especially hydroflouric acid. You can think you can handle it, but I can nearly guarantee you can't. I have a bottle of it. It's been opened once, and it's definitely THE scariest chemical you can use. Above the most sensitive of high explosives.
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Unread postAuthor: ramses » Tue Jul 13, 2010 10:29 am

Is it really a HE? I thought it just ate through glass fast enough to boil itself.

EDIT: Wow. I need to learn to read.
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Last edited by ramses on Tue Jul 13, 2010 12:03 pm, edited 1 time in total.
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Unread postAuthor: Ragnarok » Tue Jul 13, 2010 10:38 am

ramses wrote:Is it really a HE?

No. He said it's scarier to use than high explosives - and I have to agree. It's fething dangerous stuff.

Never used it, and pretty much hope I never have to.
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Unread postAuthor: metalmeltr » Tue Jul 13, 2010 11:08 am

Why do you have hydroflouric acid? I have hydrocloric acid, but you can buy that at home depot
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Unread postAuthor: jimmy101 » Tue Jul 13, 2010 6:33 pm

What are you going to coat the copper with? Without a coating the sanding and polishing is waste of time, the copper will oxide within a few weeks.

IIRC, lacquer and tung oil are often used as protective coatings on copper.
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Unread postAuthor: Hotwired » Tue Jul 13, 2010 6:54 pm

jimmy101 wrote:Without a coating the sanding and polishing is waste of time, the copper will oxide within a few weeks.


Plenty of time to get the camera out the then :P

jimmy101 wrote:IIRC, lacquer and tung oil are often used as protective coatings on copper.


I've coated none of my cannons but it might be of interest that the JustForCopper stuff used for creating the joins forms a protective transparent layer. There's strips around the joins which are as shiny as several years ago.

Can't say for sure what it is but I've heard that variations on the theme of cyanoacrylate are not uncommon for some kinds of pipe joining.

Bit expensive for coating something in mind.
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Unread postAuthor: Clarke » Tue Jul 13, 2010 7:58 pm

Just a wire wheel on and angle grinder or drill with a bit of silvo FTW.
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Unread postAuthor: inonickname » Tue Jul 13, 2010 10:39 pm

metalmeltr wrote:Why do you have hydroflouric acid? I have hydrocloric acid, but you can buy that at home depot


I do amateur chemistry..simple. It's uses are limited...but still.
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Unread postAuthor: Mpeddlesden » Wed Jul 14, 2010 7:50 am

I only used steel wool and ran it from top to bottom a few time and it seems like it weld marks really don't wanna go.
And i want to finish it and get it on here a.s.a.p Because it So Beautiful.
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Unread postAuthor: Crna Legija » Wed Jul 14, 2010 8:03 am

i use that stuff all the time to clean the burn off ss after i weld, why is it so bad?
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Unread postAuthor: paaiyan » Wed Jul 14, 2010 8:35 am

I would think it all depends on the molar concentration of the acid. In low enough concentrations it's unlikely to do any damage.
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Unread postAuthor: inonickname » Wed Jul 14, 2010 8:58 am

-_- wrote:i use that stuff all the time to clean the burn off ss after i weld, why is it so bad?


I'm gonna put it out there that it isn't hydroflouric acid. I know how much of a PITA it is to get.

Edit: I found some, you can get it with hydroflouric acid..but it's at 0.5%, with the average you'd use for chemistry being at about 70%. So, considerably less dangerous. Concentrated hydroflouric acid, just don't.

You aren't using "that stuff". You're using an extremely weak, dilute solution of it someone's prepared to be safer. If it was concentrated HF, it wouldn't be "that stuff".

Hydrofluoric acid is an extremely corrosive liquid and is a contact poison. It should be handled with extreme care, beyond that accorded to other mineral acids. Owing to its low dissociation constant, HF penetrates tissue more quickly than typical acids. Because of the ability of hydrofluoric acid to penetrate tissue, poisoning can occur readily through exposure of skin or eyes, or when inhaled or swallowed. Symptoms of exposure to hydrofluoric acid may not be immediately evident. HF interferes with nerve function, meaning that burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury.[8]

Once absorbed into blood through the skin, it reacts with blood calcium and may cause cardiac arrest. Burns with areas larger than 25 square inches (160 cm2) have the potential to cause serious systemic toxicity from interference with blood and tissue calcium levels.[9] In the body, hydrofluoric acid reacts with the ubiquitous biologically important ions Ca2+ and Mg2+. Formation of insoluble calcium fluoride is proposed as the etiology for both precipitous fall in serum calcium and the severe pain associated with tissue toxicity.[10] In some cases, exposures can lead to hypocalcemia. Thus, hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca2+ that sequesters the fluoride ions. HF chemical burns can be treated with a water wash and 2.5% calcium gluconate gel[11][12][13] or special rinsing solutions.[14][15] However, because it is absorbed, medical treatment is necessary;[9] rinsing off is not enough. In some cases, amputation may be required.
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