goldfinger1
starting to spend too much on rocks
Member since November 2008
Posts: 154
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Post by goldfinger1 on Nov 25, 2008 9:04:24 GMT -5
I have a possible project in the future where I may need to polish glass in a vibratory tumbler. Sizes will run from 1" x 1" x 1/4" to 1.5" x 1" x 1/4". Is their any reason to even change the grits since it will break over time down anyway ? It seems wasteful buying different sized grit if all you might need is one plus the polishing agent.
Steve
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rallyrocks
fully equipped rock polisher
Member since November 2005
Posts: 1,507
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Post by rallyrocks on Nov 25, 2008 11:07:14 GMT -5
As people here talk about grit "breaking down", this occurs because many of the stones are nearly as hard as the SiC, but glass is considerably softer and is not going to break down grit nearly as fast as rocks.
For glass you are going to want things to be very smooth before going into polish and I just don't think you'll get there waiting for 120-220 to "break down", my guess is you might even be able to recycle grit, because it probably won't be breaking down enough to warrant discarding after each batch.
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goldfinger1
starting to spend too much on rocks
Member since November 2008
Posts: 154
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Post by goldfinger1 on Nov 25, 2008 11:43:51 GMT -5
I would think since glass is composed of silicon oxide- it would be just as hard if not harder then some rocks. The idea was to start with a real coarse grit like 80 mesh and just leave it in the tumbler until it completly breaks down- then start the polish cycle using a prepolish or perhaps even a polishing agent like cerium oxide.
I know some glass is soft but the type I'm interested is hard with a high silicon content.
Steve
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rallyrocks
fully equipped rock polisher
Member since November 2005
Posts: 1,507
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Post by rallyrocks on Nov 25, 2008 11:55:43 GMT -5
Yes glass is harder than many rocks, but not many that make for good tumbling.
and Silicon Carbide is a lot harder than Silicon oxide.
You are welcome to try, but I think you will grind your glass away to nothing before your 80 will break down much beyond 120-220
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rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
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Post by rollingstone on Nov 25, 2008 12:55:24 GMT -5
On the Moh's scale of relative hardness, glass has a hardness of 5, most stones that people tumble (agate, petrified wood, etc) have a hardness of 7, and silicon carbide has a hardness of 9.1-9.3. Grit will break down much slower with glass than it will with agates. It will still break down of course, because the grit is also grinding against itself, not just against the glass.
The problem with waiting for the grit to break down to pre-polish size is that there is really no way to tell when that has happened. Pre-polish grit is too fine to feel with your fingers, and it would be so mixed up with the slurry that you wouldn't even be able to see it with a microscope. So are you going to wait a few weeks? a few months? a year? Because if you stop it too early, it will never polish. Also, if any grit gets trapped in a crevasse it could be released weeks later, which would mess up the entire batch. By just letting things run for weeks on end you miss out on the cleaning stages between grit changes, when you can identify issues like trapped grit.
-Don
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Post by sparkles on Nov 25, 2008 13:01:51 GMT -5
Absolutely so Don, it's a risky business and not the best course of action, there is also an issue with particles breaking down at different rates, and you only need a few large particles circulating to scratch up your "pre-polished" tumbles and ruin all that good work. Splash out and get a range of sizes, it's much better in the long run.
I have tried the trick myself, and it's not a great plan - my barrels filled with really thick sludge as the tumbles ground down - you can quickly reach a stage where it becomes so thick in the barrel that it "grabs" stones and drops them from the top on to the tumbles in the middle - causing a loud clatter and the likelihood of shatter - not what you want for your precious tumbles.
Cheers,
Sparkles.
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