jamesp
Cave Dweller
Member since October 2012
Posts: 36,561
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Post by jamesp on Jul 11, 2014 9:11:38 GMT -5
This conversation came up with rockpickforever Check out the absolute hardness. mohs 1,2,3,4,5,6..... scale is comparative and deceptive. The absolute hardness is accurate. Notice diamond is 16 times harder than quartz and 4 times harder than the next softer rock ruby. Ain't that something. And just because a crystalline quartz will scratch a quartz agate, it may require more force to scratch one vs the other. And the scratch may be way deeper in one vs the other. Point being, diamonds laugh at all forms of quartz, but some are 'tougher' or may pull harder on the diamond. And may pull the diamond particles out of the binder. If you run the blade on slow speed feed the coral about has no wear effect. The old fellow that got me into coral split thousands of large corals over 30 years on his 24 Highland using the same blade. He just put the feed on slow. Same as making cabs, guessing that pushing lightly would save the diamond wheels. Mohs hardness Absolute hardness Image 1 Talc Mg3Si4O10(OH)2 1 Talc block.jpg 2 Gypsum CaSO4·2H2O 3 Gypse Arignac.jpg 3 Calcite CaCO3 9 Calcite-sample2.jpg 4 Fluorite CaF2 21 Fluorite with Iron Pyrite.jpg 5 Apatite Ca5(PO4) 48 Apatite crystals.jpg 6 Feldspar KAlSi3O8 72 OrthoclaseBresil.jpg 7 Quartz SiO2 100 Quartz Brésil.jpg 8 Topaz Al2SiO4 200 Topaz cut.jpg 9 Corundum Al2O3 400 Cut Ruby.jpg 10 Diamond C 1600 Rough diamond.jpg Read more: forum.rocktumblinghobby.com/thread/66556/quite-indonesian-coral-close?page=2#ixzz37AXdqUmN
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Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,487
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Post by Sabre52 on Jul 11, 2014 11:54:14 GMT -5
Very interesting post. A soft touch on diamond wheels and a slow feed on diamond blades absolutely has a huge effect on wear. I personally find that, though all quartz gems are pretty similar hardness, toughness is definitely a factor. Don't know exactly why but, for me, quartz gems with an organic component ie. Pet wood and especially palm root, seem to be way tougher to cut than something like a banded agate. That has always seemed odd to me because included quartz gems like jasper or jasp-agate seem to be easier to cut than banded agates. I'd think the jasper and the wood /root would cut about the same, but not for me .
Then you get into things like jade and rhodonite. Some jades cut easy and some really hard even though they are softer than agate. And, rhodonite is a booger that seems to pull the steel over the diamond in a heartbeat. Then there are the materials like rhyolite that seem to suck the coolant up and dry out the cut, no matter how hard they are and how fast your feed. Definitely more than just absolute hardness to consider when doing lapidary work......Mel
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Post by fantastic5 on Jul 11, 2014 12:04:22 GMT -5
This thread helps me understand a few things. When I was first shown how to use my Genie I was told to press hard enough to indent the soft wheels so that they cup the stone. I don't have the chance to cut and polish very often (work and family take precedence) but I have already had to replace the first soft wheel on my Genie 3 times in 5 years. Is this because I am applying too much force and that a softer touch would better suit the diamond wheels?
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quartz
Cave Dweller
breakin' rocks in the hot sun
Member since February 2010
Posts: 3,352
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Post by quartz on Jul 11, 2014 12:21:06 GMT -5
I made a living as a machinist and millwright for over 40 years, and have been playing w/rocks about half of that. Also had the opportunity to do a little teaching. I've ground lots of different things. The one thing a person has to develop when grinding anything {and sawing a rock is actually grinding a slot in it} is a feel for what the grinding tool {wheel, disc, or blade} will do. Pushing beyond the capability of the tool doesn't speed the process much, but sure wears the tool quicker. After learning this for myself, I've always encouraged people to start out soft and work up, the machine will tell you when it's at a practical limit.
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QuailRiver
fully equipped rock polisher
Member since May 2008
Posts: 1,640
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Post by QuailRiver on Jul 11, 2014 13:11:38 GMT -5
Very interesting post. A soft touch on diamond wheels and a slow feed on diamond blades absolutely has a huge effect on wear. I personally find that, though all quartz gems are pretty similar hardness, toughness is definitely a factor. Don't know exactly why but, for me, quartz gems with an organic component ie. Pet wood and especially palm root, seem to be way tougher to cut than something like a banded agate. That has always seemed odd to me because included quartz gems like jasper or jasp-agate seem to be easier to cut than banded agates. I'd think the jasper and the wood /root would cut about the same, but not for me . Then you get into things like jade and rhodonite. Some jades cut easy and some really hard even though they are softer than agate. And, rhodonite is a booger that seems to pull the steel over the diamond in a heartbeat. Then there are the materials like rhyolite that seem to suck the coolant up and dry out the cut, no matter how hard they are and how fast your feed. Definitely more than just absolute hardness to consider when doing lapidary work......Mel I agree, the amount of friction does play a big role in wear. And there is definitely a big...No, HUGE difference in the hardness or toughness of various agates. Kentucky Agates are very difficult to saw compared to most other agates I've cut. I'm not sure if it is the type of crystal structure, the presence of a certain element or mineral that is not common in other agates, or if they are just denser and have a more compact crystal structure. Maybe even it has something to do with having had the weight of two or three hundred feet of limestone bearing down on them for a couple hundred million years? Ky Agates have a lot of internal stresses and many times after slabbing pieces, after a period of time I've had slabs crack on their own, days or weeks after slabbing. But the toughest agate I have ever tried to slab was a piece of Stromatolite last year. I've sliced several pieces in the past without issue but I bought a piece last year that was about 4" thick by 7" long. Even with clean oil and a freshly dressed blade it would stall my 18" saw and trip the thermal switch. I finally gave up on trying to slab it. Larry C.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,561
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Post by jamesp on Jul 11, 2014 13:28:12 GMT -5
Hardness and toughness are difficult properties to put numbers on in many materials. If it cuts or grinds slow, like Larry says, take it slow. Or the cutting tool will suffer.
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