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Thread: Pits in metal after barrel polishing

  1. #1
    Join Date
    Mar 2021
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    Default Pits in metal after barrel polishing

    Hello Everyone!

    I was wondering if you could help. I recently purchased a tumbler to tumble my brass and sterling silver jewellery. I'm using mixed stainless steel shot and a bit of washing up liquid and tumbling my pieces for about 30 mins. I'm using it both to work harden (after soldering) and give a shine to the metal and am buffing to 1200 grit before tumbling.

    Whilst my pieces are coming out shiny, they're also coming out covered in tiny pits. How can I stop this from happening?

    I've been reading forum posts from others and can confirm that the metal is not pitted before being placed in the tumbler (and that it's not just a case of me being unable to see the pits because of sanding marks).

    Someone suggested putting pebbles in the tumbler and running it for a few hours to blunt the ends of the pin shaped shot (which could be causing the pitting) but I'm worried about ruining my tumbler/shot. Has anyone tried this?

    Any input/solutions would be super, super appreciated!

    Thank you!

  2. #2
    Join Date
    Jul 2017
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    459

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    I'd just take out the pins to be honest. I just use round steel shot, a mixture of 1, 2 and 3mm balls and putting is never an issue.
    There's also a fair bit of evidence that tumbling doesn't work harden, maybe a few microns of the surface but that's all.

  3. #3
    Join Date
    Jul 2009
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    Tumblers are designed to polish rocks/stones (hence rock tumbler) so they certainly won't do any harm, but it might take a while to blunt your pins if that's the problem. I have pins in my preferred mix, but they're over 10 years old, and were very high quality in the first place, so don't mark anything.

    You can either take the pins out completely, or take them out and polish off the end of each one (not as bad as it sounds). Alternatively, you could get another shot mix.

    I agree very much with the above, tumbling doesn't really harden anything, but it should be giving you a decent shine.

  4. #4
    Join Date
    Mar 2021
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    Hello again!

    Thank you for your help.

    I spent an hour or so fishing out the pins and then ran a piece in the tumbler but the texture is still odd, more even but still a pitted texture (the shine is definitely there though). It's subtle-ish but I'm still not terribly happy with it in comparison to a good old polish with a pendant motor. I might just stick to the pendant motor with my new found knowledge that barrelling doesn't actually work harden either.

    Also about running rocks in the tumbler, I can't believe I didn't think of the fact it's actually meant for rocks! What a muppet.

    Maybe the pitting is to do with the fact I'm tumbling flat pieces and not textured pieces? I can imagine it would give a nice finish on something very textured but the pitting (however slight) is just very noticeable on larger flat surfaces. Just a thought.

    Anyway, thanks again!

  5. #5
    Join Date
    Dec 2009
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    Central London
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    Several things spring to mind.

    Firstly, your barrelling time is rather short. About three hours is what it would take to get a good finish.
    It also allows the pinpricks to multiply to the point that they coalesce and show less. however wire work and textured pieces fare best.

    Secondly, washing up liquid should be the most basic, without additives, but I am still convinced that a dedicated barrelling soap gives superior results.

    Rotary barrels have been in vogue for a long time, but magnetic polishers which work by a rotating magnet in the base, are said not to have this pitting problem.
    Their price was rather high originally, but they are now more affordable. Dennis.

  6. #6
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    I hadn't spotted the time - Dennis is absolutely right, thirty minutes really is a bare minimum - I tend to run a tumbler overnight (it's quite safe - they're designed to run for weeks on end). I do wonder about your shot mix if you're still having problems though - I don't think mine could leave pits in anything if it tried, it's far too smooth.

    I use a magnetic polisher as well, but the finish is always very slightly matte compared to the tumbler.

    I use a liquid brightener for both machines - our water is too hard to work well with barrelbrite, but I also think I get better results than from using even the kindest of washing up liquids.

  7. #7
    Join Date
    Oct 2016
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    103

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    Quote Originally Posted by mizgeorge View Post
    I hadn't spotted the time - Dennis is absolutely right, thirty minutes really is a bare minimum - I tend to run a tumbler overnight (it's quite safe - they're designed to run for weeks on end). I do wonder about your shot mix if you're still having problems though - I don't think mine could leave pits in anything if it tried, it's far too smooth.

    I use a magnetic polisher as well, but the finish is always very slightly matte compared to the tumbler.

    I use a liquid brightener for both machines - our water is too hard to work well with barrelbrite, but I also think I get better results than from using even the kindest of washing up liquids.
    What is the liquid brightener that you use , I am also in a hard water area

  8. #8
    Join Date
    Jul 2009
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    cotswolds
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    Quote Originally Posted by J Allison View Post
    What is the liquid brightener that you use , I am also in a hard water area
    This one:

    https://bettsmetalsales.com/brighten...elling-machine

    Excellent for both machines, and needs literally drops. I decant it into a smaller bottle with a pipette lid to avoid using too much.

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