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Post by cabby on Sept 21, 2024 14:02:37 GMT -5
The first thing I plan to be lapping is thundereggs and geodes. Ready to start making magnetic discs for it but have TOO many options! I primarily have tri-m-ite silicon carbide paper. Listing all of my options below. With using just these (or very little additional expense), what would you recommend for my process be for thundereggs and geodes? * denotes things I have more than a dozen sheets of tri-m-ite sc papers: 80*, 100*, 120, 180, 220, 240, 280, 360, 400*, 600 also have 60 and 100 crystalite discs and a 220 diamond resin disc.  Edit: forgot to mention that I have a lot of different polishes and pad options, so would like input on final polishes too! |
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Post by cabby on Sept 21, 2024 15:22:27 GMT -5
Whoops! The crystalite discs are off the table! Didn’t know that they are specialty faceting discs and almost fainted when I saw the prices! Not gonna use those to grind down rough rocks lol
So basically just down to silicon carbide papers and whatever else I should buy.
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rockbrain
Cave Dweller 
Member since January 2022
Posts: 3,167
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Post by rockbrain on Sept 21, 2024 16:16:26 GMT -5
I'd just be guessing at the grit but I know a big determining factor is going to be how they are cut. If they have some decent saw marks I'd think you'd want to start in the 80 area. If not probably more like 120 or 220.
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Post by cabby on Sept 21, 2024 16:35:30 GMT -5
My tester was 80, figured I would want that for grinding down the nubs on slabs if nothing else. Clueless after that! Made up a 220, 400, and 600 now as well but no clue how many grits are ok to skip, or how many stages are best overall. Guessing I will need to buy finer grits as well, such as 1200 and 3000?
Honest have no clue why he had so many grits, but I only have some experience sanding wood or leather.
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herb
spending too much on rocks
Member since November 2011
Posts: 473
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Post by herb on Sept 22, 2024 8:55:20 GMT -5
My tester was 80, figured I would want that for grinding down the nubs on slabs if nothing else. Clueless after that! Made up a 220, 400, and 600 now as well but no clue how many grits are ok to skip, or how many stages are best overall. Guessing I will need to buy finer grits as well, such as 1200 and 3000? Honest have no clue why he had so many grits, but I only have some experience sanding wood or leather. As rockbrain mentioned. Where you start depends on how rough the saw cut is. What you setup is a good progression: 80, 220, 400, 600. You don't have to use every grit you have. Generally roughly doubling the grit every step is a good rule of thumb. 400 to 600 is kind of a small step, but that is ok. The next level would be 1000 or 1200. I dont know if you have one, but a polishing buff would be the final step. If you dont have a buff, 3000 grit as the last step would get you a fairly decent finish |
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Post by cabby on Sept 22, 2024 9:09:49 GMT -5
herb I definitely have polishing things! A mind boggling amount for someone that has never done this before! I haven’t seen any grits higher than 600 so I think this is when he went to the powders. I should probably make myself a master list of what “grit” all of these are and what materials to use them on… This is the thread of the powders: forum.rocktumblinghobby.com/thread/105912/mystery-powders
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Post by cabby on Sept 22, 2024 9:15:56 GMT -5
If I am ending at the 600 grit for silicon carbide, what order would I go through for things like levigated alumina, Tripoli, iron oxide, etc? Still wondering what that “first lapping compound” is but maybe that’s the next step lol
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Post by cabby on Sept 22, 2024 10:16:27 GMT -5
Been trying to look up approximate grit size of my various powders and realized that a lot of them come in a huge range, so will have to test mine to figure out what microns they are and will just save them for future tumbling.
Instead I will buy 1200 and 3000 resin discs for lapping. That leaves me with the final polish… have read that tin oxide is best but that’s something I don’t have (I think). Any good substitute, or just buy that along with the resin discs?
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herb
spending too much on rocks
Member since November 2011
Posts: 473
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Post by herb on Sept 22, 2024 12:47:17 GMT -5
If I am ending at the 600 grit for silicon carbide, what order would I go through for things like levigated alumina, Tripoli, iron oxide, etc? Still wondering what that “first lapping compound” is but maybe that’s the next step lol I think the levigated alumna would be the next step after 600. It should be somewhere around 1000 grit or so. After that you could use Tripoli for the final polish. I think the iron oxide is only used in metal work, but am not certain. It will take some experimentation to see how long you need to grind at each step before moving on to the next. With my vibratory lap, to check if a thunderegg is done at the current grit, i take a pencil and put lines across the face in a checkerboard pattern from edge to edge and the run the lap for a few more minutes. If all the lines are gone or they are all the same level of faintness then its done. If there are parts where lines are visible and others where they are not, its not done. That method should also work for your rotary lap. At the finer grits, 600 and above, you can also hold the thunderegg towards a bright light and look at it at a sharp angle. If looking straight down at the face is 90 degrees and looking at it from the side so you can barely see the surface is 0 degrees, you want to be at like 20 or 30 degrees. If you hold it right, you will see the reflection of the light source off the face of the thunderegg and be able to see the reflection looks duller for areas that need more grinding |
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