unc2three
off to a rocking start
Member since August 2017
Posts: 8
|
Post by unc2three on Sept 9, 2017 11:37:38 GMT -5
Hey everyone, I'm new to the board and new to polishing geode slabs in general. I have done lot of research on how to do it etc. I can't really afford a lapidary machine so I started with a car buffing hand rotary machine. The slabs I bought were already cut and were already very smooth with slight saw marks. I attached 600 grit sandpaper to the wheel and sanded for about 10-15 minutes. I then went to 800 grit and it was starting to get shiny, the edges are polished perfectly but I'm not getting the shiny polish look all over the rock, just the edges. I then used 1200 grit and it was a little better. But I don't understand why the edges are polished and the rest of the rock isn't. The slab is flat and even with the polishing wheel so it's not favoring the edges. Any help is appreciated. Thanks
Chad
|
|
illusionist
starting to spend too much on rocks
Member since August 2017
Posts: 137
|
Post by illusionist on Sept 9, 2017 14:20:29 GMT -5
If the rotary machine pad is bigger than the geode slab, it might be cupping over it(especially when rotating), thus focusing on the edges even though it appears flat?
|
|
|
Post by coloradocliff on Sept 9, 2017 15:34:48 GMT -5
Good morning Chad and welcome to the family. If you stick around a few hundred posts you'll really learn some cool and inexpensive ways to get your rocks shiny. Know that the polish we generally polish with is at is even finer. The finer the polish the better the shine is on most materials. Stay coarse till the saw marks are ALL gone. Get over a 1000 on the grit and that will help the shine a lot.
|
|
unc2three
off to a rocking start
Member since August 2017
Posts: 8
|
Post by unc2three on Sept 9, 2017 20:24:05 GMT -5
Thanks for the reply Colorado cliff. I went back down to 120 grit but that apparently wasn't enuf, what would you recommend for a course grit? 80?
|
|
|
Post by coloradocliff on Sept 9, 2017 21:16:46 GMT -5
Thanks for the reply Colorado cliff. I went back down to 120 grit but that apparently wasn't enuf, what would you recommend for a course grit? 80? 80 might be coarse enough. If that's what you got use it. Might take a bit longer but you'll get there.
|
|
unc2three
off to a rocking start
Member since August 2017
Posts: 8
|
Post by unc2three on Sept 10, 2017 5:51:40 GMT -5
If the rotary machine pad is bigger than the geode slab, it might be cupping over it(especially when rotating), thus focusing on the edges even though it appears flat? That makes sense illusionist, it is bigger than the geode, thanks for the reply. I'm new to this and don't really know what I'm doing yet lol
|
|
Enigman
starting to spend too much on rocks
Member since December 2013
Posts: 163
|
Post by Enigman on Sept 11, 2017 22:55:58 GMT -5
If the rotary machine pad is bigger than the geode slab, it might be cupping over it(especially when rotating), thus focusing on the edges even though it appears flat? Even if it wasn't cupping, the edges would still process faster than the center. It's basic Mechanics 101. Given an abrasive surface equal to or greater than the surface being polished with applied pressure, edges will act as a stress riser and will "feel" more pressure than open surfaces and therefore will abrade faster. If you want to hand polish the slab and get results on the inner parts of the surface, then use a polishing disk smaller than the slab and move it around to affect all areas. This affect isn't observed as much on a rotary lapping machine since the hand pressure is applied to the middle of the stone and the abrasive surface is very hard, Vibrating lapping tables don't do it much either since no pressure is being applied other than gravity and again the abrasive surface is rigid.
|
|