vera
spending too much on rocks
Member since December 2016
Posts: 259
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Post by vera on Jan 23, 2017 16:45:14 GMT -5
I was looking at some things on the Home Depot website today and ran across some grits that may be worth trying out. One was BLACK BULL Blast Media 80-Grit Abrasive Garnet Sand at the price of $28.19 for a 50 pound barrel. Another was BLACK BULL Blast Media 80-Grit Glass Beads at $24.67 for a 50 pound barrel. These are less than half the price of 80 grit I have seen on lapidary sites. Since I see so many people on the board who do not enjoy paying the high prices of grit I thought I would ask if anyone knows of a reason not to try these.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,562
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Post by jamesp on Jan 23, 2017 17:23:08 GMT -5
Hi Vera. this is petrified coral after about 4 weeks in garnet grit(bottom photo) It puts a sweet shine on petrified coral. You got to have a hard sharp grit like silicon carbide to 'cut' agate. You can use a Knoops hardness scale to compare hardness more accurately. garnet-1340 AO-2100 SiC-2480 quartz-780 Even AO(alumina) will not round agates, it is too smooth to cut much. www.tedpella.com/company_html/hardness.htmCoral, after 4 weeks in 80 grit garnet. Lol, it did not put a scratch in it. It did behave like AO 80 though, and broke down to almost polish.
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vera
spending too much on rocks
Member since December 2016
Posts: 259
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Post by vera on Jan 23, 2017 19:01:10 GMT -5
Thank you James for the explanation. I will go back to the drawing board in finding a less expensive source for grits. ;-)
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,562
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Post by jamesp on Jan 24, 2017 6:33:38 GMT -5
Thank you James for the explanation. I will go back to the drawing board in finding a less expensive source for grits. ;-) Ha ha. Been there done that. Lots of replacement abrasives for the finishing steps. Garnet does great. Cheap aluminum oxide does great, just faster than the softer garnet. For the money, silicon carbide will be the only choice for coarse grinding rocks to shape. Shame they don't sell diamond cheap. Probably 95% of my abrasive costs is coarse silicon carbide. I buy it in 50 pound lots. Finishing grits in 5 pound lots and less often. The best deal to date for coarse silicon carbide is 50 pound lots shipped in a LFRB from Kingsley North. $88 plus shipping. That may be hard to beat. If you find a better deal on coarse silicon carbide please post supplier. I think this bunch on the RTH have checked every nook and cranny for the best deals. Looks to be Kingsley.
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Post by greig on Jan 24, 2017 12:06:05 GMT -5
I was looking at the same thing and almost bought 50 lbs. I was really hoping that I had found a way to save $$ on grit. Darn it. What is being said about carbide grit here makes sense. I guess you cannot avoid the science.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,562
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Post by jamesp on Jan 24, 2017 12:16:07 GMT -5
I was looking at the same thing and almost bought 50 lbs. I was really hoping that I had found a way to save $$ on grit. Darn it. What is being said about carbide grit here makes sense. I guess you cannot avoid the science. I played it smart and called big abrasive suppliers and asked for samples which averaged 1 to 5 pounds. Got a whole shelf full of freebies. Yes, SiC is designed to maraud, like no other for the money. Not so good for finish.
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