jamesp
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Member since October 2012
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Post by jamesp on Aug 17, 2014 13:29:28 GMT -5
Been grinding it to pre-tumble pebbles w/super grinder. About 2/3rds finished. Learned a bit. This time I used the outside edge of the wheel. It is fast and controllable. And found that those wheels thread onto a bench grinder. Will turn an old bench grinder 90 degrees and mount the wheel to one side. And mount a pulley driven by motor on the other side to slow it down(retire the bench grinder motor). Set up a table so that hand can rest while pushing the stone to the outside edge of the wheel. Similar to a lapper, but using the edge of the wheel. Can also use the grooved diamonds on the flat surface on top, but it is bad about chipping. Will show photos of system when done. Will be safer than 4 inch unit at 3600 RPM. Will be similar to a ganged saw shaper. The grit is coarser and these wheels are cheap. They have a full one piece 3/16 inch thick sintered diamond plate welded to the face. Chinese make good sintered diamond material. Will run dry as I always did w/the 4 inch unit. Here is what is left of the fine obsidian: Dry Wet Old 30 grit 4 inch wheel that has shaped many a tumble New 30 grit 7 inch wheel to be mounted horizontal and slowed to 1000-1800 RPM Obsidian dust, these are run dry with breathing protection
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Post by Toad on Aug 17, 2014 14:31:57 GMT -5
Looks like a lot of work, but should speed up the tumbling process significantly.
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jamesp
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Member since October 2012
Posts: 36,154
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Post by jamesp on Aug 17, 2014 18:37:26 GMT -5
Looks like a lot of work, but should speed up the tumbling process significantly. By the time I change coarse grit several times the time may balance. Surely get quicker and prettier results. I know the grinding is faster using the outside of the wheel.
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jamesp
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Member since October 2012
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Post by jamesp on Aug 19, 2014 16:58:03 GMT -5
These have been in the tumbler 48 hours and are about ready for 220. Will leave them longer. Am tumbling them w/tumbled pea gravel sized glass, about 35% by weight. Hoping to avoid deadly frosting impact. So far, so good. But all grind scratches are gone. This stuff is fast. Turning fast at 60 RPM, but barrel 7/8 full. Removed and put on 35 RPM shafts thru to final polish. fingers crossed.
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Post by connrock on Aug 24, 2014 6:25:59 GMT -5
James the "grinder" is super but I'm more excited about the size and shape of the pieces of rough obsidian.How the heck do you break up your rough obsidian to get such nice,thick,well formed pieces? Every time I've broken obsidian rough I end up with more "flakes" then anything and the pieces I do end up with for tumbling are sort of flat rather then rounded like yours??? You may "tawk" a bit funny but you sure do know your way around rocks fella! LOL connrock
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Deleted
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Post by Deleted on Aug 24, 2014 6:43:32 GMT -5
To get more uniform tumbles i cut really thick slabs like 3/4" thick then break them up Dave
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Post by washingtonrocks on Aug 24, 2014 11:46:01 GMT -5
I thought I was the only one who used an old bench grinder to shape my tumbles. lol I can't wait to see what you come up with for your "home made" lap!
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jamesp
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Member since October 2012
Posts: 36,154
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Post by jamesp on Aug 25, 2014 2:16:12 GMT -5
James the "grinder" is super but I'm more excited about the size and shape of the pieces of rough obsidian.How the heck do you break up your rough obsidian to get such nice,thick,well formed pieces? Every time I've broken obsidian rough I end up with more "flakes" then anything and the pieces I do end up with for tumbling are sort of flat rather then rounded like yours??? You may "tawk" a bit funny but you sure do know your way around rocks fella! LOL connrock Dave1 sent hose fine obsidians Tom. They were already broken to size(or collected that size). I picked the ones easiest to shape. I did use a tile saw to 'fix' some of them. Never took a hammer to them, because of what you said. it shatters and is uncontrollable. The grinder does shape them quickly as it is much softer than agate. I am curious if using small pieces of tumbled glass is going to make good filler for rotary tumbling them. The coarse grind has really made a lot of gas. Hoping the finish stages will not build so much pressure. I will say that when grinding obsidian with the coarse diamonds small chips fly off if you feed unground material to the grinder. if you feed ground obsidian into the grinder it just cuts powder off. Like a glass cutter on smooth glass starts a deep fracture. So to shape it fast, feed smooth obsidian, which will throw small chips. To fine shape it, feed ground obsidian into the grinder- the scratches dissipate the fractures causing the small chips. I have watched knappers making arrowheads use a grinding wheel to abrade the surface before pressure flaking to control the size of the flake removed. A virgin piece of glass is one of the strongest substances on earth to resist slow breaking by bending. But fine scratches reduces it's strength 1000's of times. Glass/obsidian a crazy material.
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jamesp
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Member since October 2012
Posts: 36,154
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Post by jamesp on Aug 25, 2014 2:21:06 GMT -5
To get more uniform tumbles i cut really thick slabs like 3/4" thick then break them up Dave Great idea Dave. I often saw the round/oval corals in 1.5-2 inch 'slabs' to do the same thing. Or collect the flat shapes.
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Post by connrock on Aug 25, 2014 7:58:16 GMT -5
PHEW,,,,I thought that after all these years I missed something on how to break obsidian without it flaking on me! A long time ago I did cut slabs of different types of obsidian from about 1/2"-1" thick into square and rectangular shapes. If memory serves me right(LOL) I only roughed them in a rotary for a few days to round off the edges a bit and finished them in my vibe.They came out very nice and I gave the whole 10 lbs of them to a friend down in TN cuz she LOVES obsidian.I had a huge jar with a mechanical type lid,,,,,like a canning jar but huge.I got the jar from my mom many years previous and always wondered what I'd do with it! LOL
I don't know of any obsidian that is naturally in small nodules,other then Apache Tears.Do you? connrock
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Fossilman
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Post by Fossilman on Aug 25, 2014 9:41:06 GMT -5
PHEW,,,,I thought that after all these years I missed something on how to break obsidian without it flaking on me! A long time ago I did cut slabs of different types of obsidian from about 1/2"-1" thick into square and rectangular shapes. If memory serves me right(LOL) I only roughed them in a rotary for a few days to round off the edges a bit and finished them in my vibe.They came out very nice and I gave the whole 10 lbs of them to a friend down in TN cuz she LOVES obsidian.I had a huge jar with a mechanical type lid,,,,,like a canning jar but huge.I got the jar from my mom many years previous and always wondered what I'd do with it! LOL I don't know of any obsidian that is naturally in small nodules,other then Apache Tears.Do you? connrock Glass Buttes here in Oregon has such a thing....Mostly from the weather changes and people breaking up the bigger pieces to take home,leaving the little guys....
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jamesp
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Member since October 2012
Posts: 36,154
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Post by jamesp on Aug 25, 2014 10:14:05 GMT -5
I think nature makes the best obsidian tumbles like Fossilman mentioned. That is my guess. I have heard that it is laying around in mass at Glass Buttes; but us easterners can not imagine such.
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