meta7
starting to spend too much on rocks
Member since June 2010
Posts: 164
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Post by meta7 on Apr 5, 2012 12:51:23 GMT -5
I currently use the following silicon carbide grits for my rotatry rock tumbling:
50/100, 220, 600 1500
I assume that these numbers are on the ANSI scale since I am buying them in the United States.
By my calculations, 1500 grit (ANSI) = approx 12.5 microns
I am looking for silicon carbide that is somewhere in the 3000 - 6000 grit range (or 6.5-3.4 microns) to use as the next step/pre-polish.
As I have looked online for these super fine silicon carbide grits, it seems that most or all of them are rated on the FEPA scale. Can someone tell me how to convert from FEPA to ANSI? Also, if only the FEPA measurement is listed and also the microns, will the microns measurement be the same as the ANSI microns measurement? In other words, are all micron calculations the same thing?
Finally, does anyone know of someone that sells this range of Silicon Carbide that I am looking for?
Thanks, :-) Dave
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meta7
starting to spend too much on rocks
Member since June 2010
Posts: 164
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Post by meta7 on Apr 5, 2012 13:19:57 GMT -5
I always hate being the 1st one to respond to my own post, but now (as I am researching all of this on the internet), now I am wondering if these silicon carbide grit sizes that we all talk about (100, 220, 600) are actually micro mesh sizes and not ANSI sizes? Does anyone know what the classification is?
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Minnesota Daniel
freely admits to licking rocks
A COUPLE LAKERS
Member since August 2011
Posts: 891
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Post by Minnesota Daniel on Apr 5, 2012 23:09:06 GMT -5
Microns is microns.
(American Standard) Grit to Micron Conversion It's just approximate, it's not a linear scale. Grit ---- Micron 100,000 - .25 60,000 - .5 15,000 - 1 8,000 - 3 5,000 - 4 3,000 - 6 (Missed it the first time, thanks John) 1,800 - 9 1,000 - 18 500 - 35 220 - 90
It might exist as a raw material (for example, used in the manufacture of sand paper), but I've never seen graded SiC finer than 1,500 or 1,800 grit offered for sale in any lapidary context.
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Post by johnjsgems on Apr 6, 2012 8:36:31 GMT -5
Why not just run it longer? It breaks down finer as it works. It isn't rocket science. You could probably run 600 for 2-3 weeks and have same result as doing all the fine grit steps. By the way, missing from the chart above is 3000 grit which is 6 micron.
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Post by johnjsgems on Apr 6, 2012 8:37:58 GMT -5
Also, most of the "tumbling grade" aluminum oxide polish compounds are in the 3-4 micron range.
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meta7
starting to spend too much on rocks
Member since June 2010
Posts: 164
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Post by meta7 on Apr 7, 2012 9:34:17 GMT -5
John,
I have not experimented that much with tumbling extra weeks to break down grit and get a finer finish, but the times that I have tried it with the 1500 SC on quartz, it did not seem to make that much of an improvement. (even when I tumbled for 3 weeks on 1500 [after the 60/90, 220 & 600 steps]
I have a feeling that one more step of SC (past 1500) will make a difference because once I transition to aluminum oxides (after the 1500), the polish gets better, but they do not remove the scratches that the 1500 made. They only seem to polish over the rock. Even when I use my coarsest AO (8 microns).
As far as the different rating systems go, I am still trying to figure out the ratios between micro mesh, ANSI and FEPA. And also try to determine which products are rated on which scale. I called Lortone and they did not even know! The tech guy (who was very helpful) e-mailed me back later and said that it was on the FEPA scale for >= 240 grit, and on the mesh scale for < 240 grit.
I still have a lot of figuring out to do with all of this because all of the info I have gathered (mostly on the internet) is very ambiguous.
Also, I am going to order some of this finer SC on Monday and just experiement with it and let my eyes determine how much finer it is.
I will post my results in a few weeks when I have tumbled with these finer grits.
:-) Dave
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Post by johnjsgems on Apr 7, 2012 12:21:58 GMT -5
Just a guess but I think the 1500 doesn't put scratches in but rather shows scratches from earlier steps. If the finer grits don't make a real improvement then the 600 you run has broken down to something really fine. If it looks worse after 1500 you are going backwards. Back when I was home more and tumbled I ran 600 for one week and then polished. The cooperative rocks always came out fine. Softer stones would be helped with a tripoli pre polish.
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jspencer
freely admits to licking rocks
Member since March 2011
Posts: 929
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Post by jspencer on Apr 7, 2012 22:42:44 GMT -5
I must say that I didn`t even know s/c was made using that high of grit count. 1000 is the finest I have ever used followed by a a/o prepolish then on to polish. I agree also that it may be the scratches just become more apparent as they smooth. :2cents:
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