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Author Topic: Tumble polishing of copper/brass  (Read 8113 times)
sidecar_jon
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« on: July 22, 2010, 09:34:37 pm »

I've been making small copper pieces, one problem is i'm polishing them on a polishing mop attached to a drill clamped in a vice. Out of ten i make, i usual get eight with two pinging off round the shed never to be seen again or threatening to end up in my forehead.
On investigation on the net i've found that a tumbler might do what i need with little risk. I acquired a Kilo of stainless steel shot, which is all different shapes, planets spheres and pins etc. Thinking i could use an old National Geographic tumbler i found in a charity shop for £4.

However results so far have been very disappointing. The copper coming out a bit cleaner but nowhere near the promised bright and shiny. I think the motor just isn't up to a kilo of shot, its sluggish and the shot doesn't seem to fall on the copper bits, just slosh around.

Proper rock tumblers seem to be about £60, which is a bit beyond me with its unproven usefulness. Anyone tried this method? Any tips? I'm thinking of rigging up one of the various electric power tools i have round to turn a bigger drum a bit faster....
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GreyCorbin
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« Reply #1 on: July 22, 2010, 10:24:08 pm »

I found these sites if you want to DIY.

http://www.ehow.com/how_4964435_make-rock-tumbler.html

http://ktcatspost.blogspot.com/2007/01/diy-rock-tumbler.html

http://www.miim.com/thebside/tumbler/index.html


During the search i noted that there are different grit choices, as well.  You might get different/better effects with different grits.
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« Reply #2 on: July 22, 2010, 10:27:46 pm »

Tumble polishers usually have a soap (not detergent - I used saddle soap) as well as the shot (as it sloshes in the bottom I gather you've got water in)

The different shaped shot (ball, pointed wire) gets into all areas of the brass including holes,etched lines etc.


Depending on how much you're tumbling you could try using polishing grit instead of using the shot, so as the bits of copper rub each other they sand themselves with the grit.

http://www.hswalsh.com/items.aspx?t=132
http://www.ukge.co.uk/uk/grits.asp
http://www.cooksongold.com/Jewellery-Tools/Polishing-Grit-H1-500---Fine-1kg-prcode-999-011&p=gs
http://www.manchesterminerals.co.uk/acatalog/Polishing.html

Different grades of grit are available, as with emery paper, depending on how marred the copper is you may start on course, then medium, then fine.  

I've used one of those national geographic tumblers and they're not too powerful.  How long are you leaving them in the tumbler.  With this bit of kit I found that I used to have to leave stuff in it  for eons.
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Mr. Boltneck
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« Reply #3 on: July 23, 2010, 06:05:29 am »

There are a number of less weighty options out there for part tumbling, including various mild abrasives, ceramic balls, and media like corncob pieces and crushed walnut hulls. Just as an example: http://www.eastwood.com/buffing/vibratory-tumblers.html
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Captain Quinlin Hopkins
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« Reply #4 on: July 23, 2010, 11:40:16 am »

the interesting thing about different grits, is that they eventually break down to smaller and smaller pieces.  So if you left it tumbling for a month or two, you might get an interesting polish.  Problem with stainless metal bits is that they are not going to really wear down.  You are not polishing then, simply cleaning them as would a person who reloads their own ammunition.  You could always try dropping a bottle of brasso or similar and letting it run for a week and see where you get.  The smaller, less powerful tumblers are known to run for weeks at a time to get polish on rocks, can't see why metal would be easier.
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« Reply #5 on: July 23, 2010, 12:33:12 pm »

I have only ever used the stainless shapes for deburing never for polishing. They went into a seberate vibrator with little cones made from the same stuff as oil stones with lots and lots of a liquid polishing compound,came out looking like a mirror!

It took more or less a full shift (12 hours) to get them right and the customer paid more for the polishing than the machining!!!! Like they say its the finishing touches that count Wink
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sidecar_jon
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« Reply #6 on: July 23, 2010, 03:10:08 pm »

Well today ive had the poor old tiny tumbler going all day, i fully expected it to burn out, bt it hasnt yet...i will have alok latter and see what its done...
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sidecar_jon
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« Reply #7 on: July 23, 2010, 03:24:37 pm »

Well ie just had a look and after seven hours of tumbeling (an hour is recomended, but after an hour it had doen nothing) ie produced an impressive amount of yellow froth. Little else though, the copper is dull but has lost its surface blackness, but its in no way shiny. I have now washed it and thinking my soap was wrong im trying some diferent soap....we will see ah!
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Captain Quinlin Hopkins
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« Reply #8 on: July 23, 2010, 04:23:48 pm »

Yes, cleaned is a good step  now a thorough washing and changing out the medium to something finer is going to be a necessary evil.  Talk to someone in the local area who collects rocks and fossils.  you might even be able to borrow a small quantity of tumbling polish if you ask nicely enough.
That stainless is simple not going to break down before you are left with a brass soup.. 
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sidecar_jon
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« Reply #9 on: July 23, 2010, 06:51:38 pm »

Well stainless steel shot is what jewellers use to polish silver and gold items.. Grit etc is for stones etc, though i might give them a try sometime.
 Anyway this time i concluded the stuff i used as an additive was detergent, so i cut a chunk off the bathroom soap bar and with little hope i chucked that in the washed mix. After and hours i was surprised to find that it was indeed producing a much better result. Shiny even!....experimentation continues.
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hardlec
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« Reply #10 on: July 24, 2010, 03:05:42 pm »

Jewelers use shot with a liquid, and there are various kinds of liquid, to polish on gold and silver. 
There is sometimes a series of steps in a tumble polish, and when I did tumble polishing I had 3 different tumbling containers, transferring items from "Coarse" to "Fine" to get a bright finish. It seems the instructions that you got are incomplete and inaccurate.  You may want to access the Rio Grande web site.  Rio Grande sells supplies to jewelry makers. They sell many varieties of supplies for mass finishing.  (I am not savvy enough to post links, sorry.)

You may want to find a gun shop.  Reloaders use a special compound (walnut shells and jeweler's rouge, I think) to clean the brass part of cartridges prior to reloading.  Brass, Nickle Silver and other Copper based alloys use similar chemicals.  A rather different set of products is used for ferrous metal.
 
There is the "good ole" brasso, which is ammonia and chalk dust with enhancers.  It is applied with elbow grease, an often disparaged method, but one that works with awesome regularity.

Your rock tumbler may not be right for the job.  There are sonic and centrifugal "tumblers" now, and they have different requirements. (You may have the wrong shot for your tumbler.)  On the other hand, the old school rock tumblers were intended to use sand, water and the object stones and tumble them for weeks.  Running your tumbler for a few days should not harm it.
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sidecar_jon
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« Reply #11 on: July 24, 2010, 08:32:29 pm »

The idea of shot is to peen and polish, grits etc grind away bits to round off stones. Results so far are good for bathroom soap and stainless steel shot. And surprisingly not very agressive. I left it going all day today and it seems there is little to gain after about and hour of tumbleing. I seems a good technique if you are making lots of bits but for individual one offs, a wheel is better.
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