rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Dec 14, 2011 2:00:47 GMT -5
I have some WAY cool agates from Kazakhstan that I'm trying to polish in my 20" Lortone vibe lap. They are like 8-10" across and probably weigh 2-5lbs each. I'm pretty sure the agates are flat - did the pencil test on all 3 grits, 120, 220, and 600. Problem is that there are areas near the center or to one side that aren't getting as shiny as the rest of the rock. Anybody have any experience with vibing really big agates/t-eggs?
Here are some of my guesses, though they might all be wrong:
1) The matted areas SEEM to correspond to portions of the rock that aren't as thick as the rest. Now, I've done slabs where I had to put more weight on one end because of it being ground down to take out saw marks or those dadgum NUBS(!!!) most sellers leave on them with the usual furrow dug in just before it. Might I have to put some weight atop the thinner part of these 2 nodules to get it all shiny?
2) Might the polish be getting pushed away by the outer edge or the "leading edge" of these guys? These dudes are half again to 3x as big as the rest of the ones in the pan and so they go wherever they want. Eventually, they find their "happy place" and end up always at the edge of the pan and in the same orientation/direction. Might I need to periodically dump a spoon of polish directly under these huge agates so that the light areas don't get "starved"?
3) Might my pad be starting to get kinda thin and these rocks can't sink into it? I'm thinking this might not be the problem because on of the big aggies was in the first batch i did with a brand new Kingsley polish pad.
What do y'all think? Any ideas or tips on doing really big nodules. Hope so because I have some 8-12" slabs I wan't to do, as well. Thanks! Rick
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Post by jakesrocks on Dec 14, 2011 9:46:16 GMT -5
Try grinding a shallow bevel around the outside of the nodules. As they grind flat, the sharp edges tend to push the grit away, instead of letting it get under the piece.
Those sound plenty heavy enough. You shouldn't need any more weight. Don
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Post by johnjsgems on Dec 14, 2011 20:41:35 GMT -5
The bevel also helps prevent tiny pieces breaking off the edges and becoming scratch makers. I had a Lortone vibe lap that always frustrated me. Out of four big flats at best two would come out nice. I never had a better quality lap but never had a non-uniform finish if the surfaces were completely flat before polish. I used cerium on the lap but have heard since that nothing works as well as tin oxide.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Dec 15, 2011 17:29:22 GMT -5
Yeah, I had already beveled the edges. But some areas were hard to reach - concave - without possibly gouging the rocks with the edge of my spinner lap. I did one and it turned out somewhat better (19hrs) but it still needs more time in the pan. It's about 9" x 5" and point and lighter on the pointy end. Maybe 5-6lbs. It's still a little dull right in the middle.
I put in a Kentucky agate that's roundish and very uniform thichness like 9" and maybe 7-10lbs that had turned out dull in the middle when I first started doing this stuff a few months ago but it didn't improve a whole lot. I had even applied grit to the center agout 3hrs into the vibe.
The other Kazakhistan agate turned out a good bit better. It's *only* 7" and roundy. What I did with it was tape a good size rock over the thin side of it. Might be also because it's not as far from the edge to the center of it, though. The long, pointy Kazakh always gets itself running longways around the edge of the pan, occasionally swapping which end is leading so the center of it is always being starved of polish(?) Maybe I can figure some way to make it go sideways.
More later - and thanks! Rick
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Dec 15, 2011 17:35:36 GMT -5
Oh yeah - The new pad I ordered just showed up so I'll try it out. Might wait and see if I can find a piece of carpet as was recommended since that is thicker. Tin Oxide ain't cheap! BTW - Why the heck is it that just because China was pissed at Japan and raised/limited THEIR supply of rare earths the prices jumped in the US, too? Doesn't sound right as China didn't include us in that bit of nastiness...
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Post by Jack, lapidaryrough on Dec 15, 2011 18:32:10 GMT -5
rykk.
you should face sand with glued grit paper or disk, same as your last grit used on lap. loose grit grinds are very hard to get a good polish on. i to run large laps. ( 24" & 20" )and found out the hard way. Though i only use 220 grit on all my laps. though i well face sand and grind a bevel as needed. After lapping with 220 grit, I`ll face sand with 320. and a worn out 600 grit belt. Then i use a 24" lap. The lap i use has 1/4 inch lambs wool carpet on it. i polish with cerium oxide.
Oh to add i use a Fulmer 20" lap only for the polish stage. Both of my Highland-Parks 27" are for 220 grit only.
And for the bumper rings i use seal rings from irrigation pipes 4" - 6" - 8". Many ideas out their for bumper rings.
Jack
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Dec 18, 2011 0:59:06 GMT -5
All I have is an 8" Inland spinning lap and the 20" Lortone. I grind the nubs off (hate those!!) and try to knock down the saw marks with a 100 grit diamond lap and then do 120, 220, 660, and then tin or cerium oxide. These 3 rocks are/seem WAY too big to do on a belt/expando.
Where can you get lamb's wool carpet? Or how can you tell what it is? I was thinking of using some outdoor pile carpet like is in some boats or like is used on covered porches (not the astro-turf kind). Would that be any good?
I won't get the big guys back into the pan uintil Sunday. Had to do a lot of cleaning and acetone soaking to get the contact cement from the old pad off and I'm letting the new one set up good b4 I try it out. It really does seem like either the centers of rocks over 5-6in wide are either not getting polish like the outsides do or, God forbid, it might be the same "physics" problem that seems to keep anything over cab size from polishing the middle on a spinning lap. Or maybe it's because they are just so darn heavy? Reckon all I can do is keep jiggling them untill the centers shine up. C-ya, Rick
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Post by jakesrocks on Dec 18, 2011 11:54:36 GMT -5
If you have an RV repair or supply place near you, look for the material they line the basement storage cabinets with. It's some sort of synthetic felt. Does an excellent job of polishing, and lasts a long time. They may even give you their offcuts, just to get rid of them.
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Post by Jack, lapidaryrough on Dec 18, 2011 13:18:16 GMT -5
rykk.
Forgot to add this. Most important when using a lap ( vibrating ) that the pan is covered to maximum. if the rocks stop moving - take one smaller stone out. the material should move slowly in a one direction. You may know this, I`ll say it though. Don`t use to much water lapping stone. Some material i only use 220 grit & white tooth paste for slurry mix. with very little water. per-mixed then added to plate. Not to wet / or dry.
friction is best - though too dry the stones well walk over each other and out the door.
most carpet stores sell lamb wool carpet. reason its good to use is the wool is carbon and hold the polish better then plastic or oil base fibers.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Dec 18, 2011 23:25:49 GMT -5
Jack - Thanks. You just reassured me that I wasn't overfilling the pan! lol That said, I DO only fill to maybe 90% and the rocks tend to orbit the pan fairly fast and do a lot of swapping of positions. Except the huge ones that claim their spot and tend not to change orientation very often. I'll experiment with this. I'm thinking maybe it's better to have all the rocks close to the same size, too, because it's the little ones that get shoved around and tipped over by the bigger guys. I just put in lots of different sizes because A) That was my habit from tumbling and B) Well, those were just the ones that were ready for whatever stage.
I'll see if I can't round up enough good size nodules to slow these 3 giants down some. (fixing to be 4 - I just picked up another Kazakh "Maizkhoje" chunk) I'm, also, thinking that I might even rig something to hold the biggies still in the middle of the pan and just dump a teaspoon or so of TiO2 under the dull areas every few hours and see if that doesn't help.
Jake - I think I know, now, what kind of carpet/felt you're talking about. I'd read your tip about it elsewhere here but your description now tells me what the stuff is. Though it's gonna cost me having to get yet another pound of polish, I think I might find some at a van customizing shop or - being in "rockhound hell, Florida" - maybe a boat marina.
Gonna go and reload the pan with the new pad now - I'll let y'all know what happens. Thanks a TON for the help! Rick
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Dec 22, 2011 0:11:53 GMT -5
Ok, so the two big guys turned out well. The giant Kentucky could maybe wiggle for another 8 hrs but it looks fine. The big, long Maizkoje agate turned out perfect. At least rated against my results - lol.
I used a brand new pad and jiggled them for 2 days. What worked for the 9in long Kazakhistan Maizkoje agate was to crowd the pan so much that he couldn't move far from the orientation I chose for him which was perpendicular to the edge of the pan rather than his usual spot orbiting long ways around the pan.
The 10 or 11" Ky agate is roundish and almost pentagon shaped and maybe 3 1/2' thick tapering to a sharp edge all the way around. All I could do with him was to lift one side every now and then and dump a little extra TiO2 under the middle.
Not sure if it was these things, the new pad, or just a bunch of time in the pan but all's good, now. I would have expected them to take less time than the smaller, lighter rocks but they ended up taking a long time. When this pad wears out, I'll swap in a piece of carpet. Maybe the thickness will help with these monster rocks. I have an even bigger Kazakhistan agate coming that I lucked out on at ebay and I'll see how that one goes.
Thanks y'all and Merry Christmas! Rick
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Post by johnjsgems on Dec 26, 2011 18:05:56 GMT -5
I guess it is too late now but if the pad fits snug in the pan you don't need to glue it down. The outer bumper ring will hold it down (and the rocks).
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