jamesp
Cave Dweller
Member since October 2012
Posts: 36,371
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Post by jamesp on Jun 8, 2018 6:18:25 GMT -5
Thats right. Should be the same for rocks. I primarily tumble small flats of glass in coarse grit at 30 or 80 RPM. Over and over and over. It only takes 1 to 3 days and coarse stage is done. About 50 loads in the past 4 months. 30 RPM makes pendant sized flat pieces get thinner in thickness. 80 RPM makes them lose edge material.
I melt glass in a kiln and glass always free melts to 6mm to 7mm thick. A bit thick for pendants. Even if you start with 3mm thick glass in kiln it will shrink in surface area to 6 to 7mm thick when melted. The nature of molten glass.
My tumbling theory is the pieces slide across each other on their flat faces at slow speed. Less tumbling and more sliding in barrel. And strike each other on the edges more so at higher speeds where more tumbling motion is created.
The reason I have had to run coarse on glass at 30 RPM is because of the warmer temperatures recently causing more gas build up. Even overnight. At 80 RPM the gas was being created quickly and blowing the caps off my barrels in 24 hours in these recent hot temps. Two blow off's in three days last week. 30 RPM wears slower and cuts thru less glass bubbles where the high pressure gases are. Gives me a chance to burp them daily before caps blow. Substantial loss in thickness when opening two barrels yesterday running glass with SiC 60 at 30 RPM. Seen this several times. A repetitive outcome. This is good news because I often need to thin my glass without reducing the silhouette area.
Barrel speed has a big influence on grinding speed in coarse stage. Higher speeds way increase abrasive breakdown and conversely rock wear. No doubt about that. But how it shapes flat material never registered till recently.
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tkvancil
fully equipped rock polisher
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Member since September 2011
Posts: 1,546
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Post by tkvancil on Jun 8, 2018 7:45:20 GMT -5
Perhaps this is one reason larger commercially produced barrels are multi-sided.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,371
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Post by jamesp on Jun 8, 2018 8:21:01 GMT -5
Perhaps this is one reason larger commercially produced barrels are multi-sided. Never thought about hex barrel effects Ken. These were run in round barrels for what it's worth. But the hex barrel may induce more sliding. I think I read where hex barrels can rotate faster with less damaging action than round barrels. I could not understand why I was losing the widths on my pendants when wanting to reduce the slower thickness dimension. It was causing me to make the pendants bigger to make up for the loss of widths. Took a while before the light turned on. Actually disconnected that 80 RPM set of shafts, they were shrinking my product.
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