Thread: Remove machining marks in brass?
18th Oct 2007, 01:40 AM #1
Remove machining marks in brass?
How do I remove machining marks in brass, and go on to a mirror finish?
I have just completed a brass component, basically it looks like a Gent's ring, 40mm in dia, 6mm thick, with a large hole in the centre. It's not a ring, but a frame for a rare coin.
The finish on the OD was finely serated, left by the carbide tool. I figured a quick lick with 800 wet and dry would do the trick, but not so.
It now looks like it's been sanded, so, what else do I try?
Some thoughts are polish the OD with fine valve lapping paste, then finish up with Brasso. Or may be an automotive cutting compound?
This frame will be gold plated as the final finish. Perhaps I should just leave it the plater's to polish.
Any comments are welcome, the art of metal polishing is something I would like to know.
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18th Oct 2007, 07:22 AM #2
Marks in brass
I have had success in using a scotchbrite kitchen scourer on brass and aluminium after wet and dry ,used wet while item was still in the lathe.
I used a mix of Brasso and abrasive hand cleaner as that was what was available at the time.
18th Oct 2007, 07:46 AM #3
Perhaps I should just leave it the plater's to polish.
That's probably not a bad idea. I've had a few aluminium components anodised and I can't match the polishing they do.
18th Oct 2007, 08:32 AM #4
Try toothpaste.Its got a very fine abrasive agent in it.
18th Oct 2007, 10:47 AM #5
Err . . . . what's wrong with a buffing wheel and buffing compound?
If it's only 6mm thick the cloth wheel should be able to lick the inside of the ring to polish it.
18th Oct 2007, 11:38 AM #6
Umm, do you really want to place a rare coin into a brass mount, best way to destroy value of the coin after cleaning. "Ex-mount" coins are worth around 10% of book value.
Brass is the same as wood and everything else, work your way through the sand paper grits up to 2000 odd then hit it with a metal polish.
18th Oct 2007, 07:10 PM #7
100 mm dia. aircraft alloy ,I used the finest feed and highest speed for a nice finish .
Then polished it by starting with 600 wet and dry and kero as the lube went to 800 then 1000 and 1200 then finished it with Eagle mag wheel polish and a piece of rag .
It looks like it's chromed .
The young bloke was wrapped ."Outside of a dog a book is man's best friend ,inside a dog it's too dark to read"
18th Oct 2007, 11:44 PM #8
Spent a few years in metalwork prep and polishing. We made a range of furniture frames etc. Some jobs were a circular base of round brass tube with numerous uprights of smaller brass tube with a 3mm steel topplate which uphoslered chair mounted to, all chrome plated after fabrication. Circle bases ranged from 400mm dia to 2m dia, material 12mm dia 1mm wall to about 25mm dia.
We could get a good plating finish from tube rolled to correct circle size with a 3hp polisher driving 250mm sisal mops with standard polishing compounds, before circles were trimmed to size and brazed, without distorting the overall preformed shape.
This is done handheld freeform (with leather gloves over knitted cottons for heat protection) for the base rings and uprights. Average about 2m polished in a minute. For small items as you describe, I would use a mandrel and spin the item lightly pinched betwen finger and thumb for braking (leathers over cotton again).
If you need to polish inside and out, make male and female mandrels out of wood and polish interior with a small mop in a dremel, exterior with a mop on polisher or grinder. Polish the least critical part first, then mount on that surface and polish the most critical.
Haven't done anything for gold plating, but for chrome our platers preference was a very lightly crosshatched pattern, rather than a true mirror finish, but check with your plater for their preferences.
Don't use an abrasive belt at all, it will flatspot the job very quickly. For the radial marks, spin on mandrel about 30 degrees accross the mop edge, the radials will disapear very quickly.
Do not try this with bare hands or just cuttons or just leathers. Bare hands will blister in seconds, cottons will wear through and then blister exposed part of hand very quickly. Never polish like this with just leathers either, they have the abrasion resistance to survive but heat up quickly, and retain heat for a long time. By the time your hand warns you that the inner surface of the leather is burny hot, you will be blistered before you can get the gloves off. For long period of polishing I often run double layers of cottons inside leathers.
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