rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Feb 15, 2012 23:21:42 GMT -5
Hi, y'all - I've been polishing some Montana Agate slabs and a fair sized end slab of Mahogany Obsidian (around 5"' across, square-ish, maybe 3/4' thick) in my 20" Lortone "jiggle pan". I used tin oxide polish. After 2-3 days in the pan, the obsidian was shiny but it has a sort of "orange peel" type texture if you look close at it. Is obsidian a harder rock than most agates and does it, maybe, require a different polish than SnO to get a smooth finish? My sequence is 120/220/600/polish with SnO.
For grins, I ran it and a few other rocks I've not been pleased with for a little under 20 hours using some 1000 grit aluminum oxide I had from when I was tumbling. Haven't gotten a chance to try to rerun it in the tin oxide yet, though, because the big crown bearing that takes alll the abuse when the motor runs just started making way too much racket, so I had to order a new one from Ace along with the flanges it mounts with. Should show up Thurs. Thanks, Rick
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Post by Woodyrock on Feb 16, 2012 1:03:13 GMT -5
Rick
Obsidian is much softer, and more brittle than agate. I know nothing about vibrating polishers, so someone else will have the answer to the orange peel. Jade, is notorious for orange peel when polishing with oxides. Diamond polished jade very nicely without orange peel. Getting orange peel on obsidian is most likely due to the softness. Generally, you try to keep all stones in the same batch the same hardness. Combining obsidian, and Montana is having one very hard stone, and one very soft. You need to take the obsidian out well before the Montana. Woody
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Post by Hard Rock Cafe on Feb 16, 2012 13:29:31 GMT -5
The mixed hardness shouldn't be a problem with a vibrating lap. I can't help with the orange peel, though.
Chuck
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Feb 17, 2012 1:25:37 GMT -5
Thanks - I saw a lapidary site, once, that mentioned it but can't seem to find it amongst the 100s I have. Rick
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Post by johnjsgems on Feb 17, 2012 13:57:17 GMT -5
I've never heard of it on a vibe lap. On a hard felt wheel I had on my first machine I would get it with cerium on soft stones. By the way, cerium was always the preferred polish for obsidian but don't think the tin oxide caused the orange peel. Maybe the felt pad?
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sticksinstones
starting to spend too much on rocks
Member since February 2012
Posts: 117
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Post by sticksinstones on Feb 22, 2012 11:05:56 GMT -5
I think the first thing you need to try is to dramatically shorten the polish time. What was the last grit stage you ran before you put it in to polish it, or did you?
Obsidian will polish faster than the agates, but I don't think I ever ran the polish stage that long even on agates. The idea is to get the stones ready to polish in the finer stages (I usually ran 600 grit as the last stage before polish) so you don't need so long to try to lift a polish. I'd check it every couple of hours to see if it's done.
Are you putting any weights on the stone? That will speed polishing considerably if you're polishing slabs.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Feb 23, 2012 3:28:57 GMT -5
Yeah, I'm putting rocks on top of the smaller ones and also any that are fairly flat even if big. Can't seem to find a tire store that doesn't sell their used weights to the local recycler. Usually quartz "river rocks" from my landscape - as big as will fit without making the smaller nodules top heavy. I, also, load 1 or 2 on top of the Montana agate slabs I'm trying to do. I picked up some slate at the local plant nursery/landscaping shop that works nice for slabs.
This last batch just seemed to take that long to get a good shine. 600 was the last grit before the polish. It might be that the 600 stage might have been too short? It did shine up nice after like 3 days in tin oxide. A caveat, though - I only had less than 1/2lb of SnO and so I started mixing in a bunch of the polish that comes in the Thumler's grit kits because that's all I could get locally without waiting for online stuff to be mailed. Don't know what that stuff is, but it is sure SLOW going with that stuff. Worked great in a tumbler but that was like a week and a half of rolling. 24 hours of that stuff barely affected the dull, 600grit finish on the Montana slabs!
I'm starting to think part of my problem may be the motor I have on my 20" Lortone. (or maybe just impatience!) The original seized up a day and a half after I got it. VERY used. I remember my very first batch rough ground with that motor flattened out in less than 20 hours. Had a real hard time finding out the specs of the motor but did find an old page on the web where the guy said it was 1/15hp, 1500rpm so I picked one up at Grainger. I didn't have a decent amount of time to watch the first motor, but it *seems* that the vibration was less dramatic with the new motor. I've had the new on since summer. Maybe it needs to be slower? The new motor doesn't have an internal fan like the old one, so I had to strap a 6", 12V high velocity rack fan to the bottom of the motor, blowing up thru it and at the temp sensor to get it to not trip the thermal protection in the heat of the Florida summer after 30 minutes. Maybe that is acting as a counter-weight and hosing up the vibe excursion at the pan? Hard to remember my physics after so many (aaargh! lol) years...
I ran everything in this batch for a day in some 1000grit aluminum oxide I had laying around but am still waiting for some TXP polish I ordered last week to show up before I try to re-polish. Cheap price - hope it works! The obsidian was real shiny but not "glassy" smooth before the 1000. And Montana agates I have yet to get a glassy smooth shine on, so I'm hoping they will all shine up more glass-ily when I redo them. Thanks, Rick (cyborgsam at ebay)
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sticksinstones
starting to spend too much on rocks
Member since February 2012
Posts: 117
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Post by sticksinstones on Feb 23, 2012 23:51:02 GMT -5
If you've dampened the action on the motor with the fan then I suspect you're right - that would definitely be something to be suspicious of. Can you mount the fan on the frame so you don't have to affect the action imparted by the motor?
I'd also be extremely leery of mixing polishes. When I flat lapped they were pretty picky about polish. Keeping it at the right level of moisture (I tended to keep them pretty damp) and using tin oxide gave me the best and most consistent results. I did stuff like trying to mix cerium in and couldn't control the results. That could be part of your problem pretty easily as well.
I'd go back to a clean polish pad and saturate well with tin oxide when you can line some more up. I'd back the obsidian up a couple of stages to get it flat again and give it another go with shorter polish times. I really do thing that about 6 hrs. was the longest I remember polishing when I had things dialed in. Any longer and I'd start undercutting softer stone (e.g. the rind on coconut geodes in particular).
What are you using for a polish pad? Natural wool works best. I had people tell me they liked some artificial carpets but again I ended up with undercutting issues when I tried them and I decided to stop trying to skimp in the last stage after having all that time invested and ultimately was able to extract consistent, high quality finishes as a result.
I think your Montana agate is the most telling. That stuff should shine quite easily. The fact that it hasn't after a day tells me something (at least one) is out of whack. How long did you lap on each of the preceding stages? Ever do side by side comparison's of slabs from each stage in direct sunlight? You can notice a distinct difference in the way light reacts with the surface. I eventually got to the point that I could tell which stage a rock had last been through using that technique.
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Post by helens on Feb 24, 2012 19:07:40 GMT -5
I'm pretty sure there are clear directions in the Tumbling section for obsidian...
Obsidian is glass, so it should polish exactly like glass and opals. I found that putting agates in with my opal wrecks it, so that would hold true for obsidian too. Also, I would never put anything bigger in with the biggest piece of obsidian (because as it tumbles, it will 'fall' on the obsidian and risk chipping cracking and pitting). Nor anything smaller than 1/4", because it can drill into the obsidian.
But you might ask this in the tumbling section... I didn't even realize this section was here til a few days ago, so maybe others don't either.... tumbling isn't lapidary:P.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Feb 24, 2012 19:37:50 GMT -5
Thanks, Sticksinstones. Where can I get a wool pad for my 20" Lortone? I've been using the pads that Kingsley North sells. They do "fair" but seem to flatten out after 24hrs and this causes - I think - my larger nodules and slabs (sometimes 9-10" diameter) to not polish in the center. I'd like to find something a little thicker and more durable than whatever those are. I found, also, that those pads actually shrink like some clothes and I've had to glue them down with contact cement so that they don't start spinning along with the rocks. Does seem to put a really nice finish on the pan after a while, though - lol.
I bought some 100% wool, sorta felt-like stuff at Joann's Fabrics and thought I might try to use a double layer of it. Do you reckon it would work?
You my be right about excessive polish time. I've had a number of agates undercut on me. Especially remember a Demming agate that did. It was nice and smooth after the 600grit stage but, after polishing, it was really shiny but the white matrix had undercut pretty bad. As to the Montana slabs, those have been turning out with a "grainy" finish rather than "orange peel". I ran some using 1000grit Alum. Oxide to see if, maybe, they just needed a "post pre-polish" stage. Reckon I'll find out by Sat or Sun because my "TXP" polish just arrived today. It was recommended on this forum, so I thought I'd try it out since it is 3-4 time cheaper than Tin Oxide.
Hi, Helen - I'm not tumbling; I'm using a vibratory lap. different rock hardnesses don't matter with these. Thanks, though. :-)
C-ya, Rick ( cyborgsam - "CyborgSam" - @ebay)
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sticksinstones
starting to spend too much on rocks
Member since February 2012
Posts: 117
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Post by sticksinstones on Feb 24, 2012 20:36:55 GMT -5
I buy 100% wool carpet remnants and cut them to fit my laps. I'd definitely give the wool felt like material you found a go. You will probably have to find a few different carpet shops before you find one with 100% wool remnants.
It's been a long time since I've used vibrating laps so I'm unsure how to advise re: the Kingsley pads - might be worth a note to them to ask what they are made of.
Do you have a dedicated pan for polishing? I ultimately just dedicated a single lap to polishing, then I could charge the heck out of it with polish and always have a good polish slurry going. I have a 15" lap that was new when I set it outside in a plastic bag, but it's been there a few years now. might make a good project if you want to pick up a second lap and get one going for dedicated polishing.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Feb 29, 2012 2:32:24 GMT -5
Ok, I got a smoother polish on the Montana aggies. I only let them go for about 8hr per side. They're "ok". Smoother but they and all the other rocks seem to have a sort of foggy finish even after 16 hours. Especially noticeable with the mahogany lace obsidian. Not sure that the TXP works as well as tin oxide though it sure cleans off of the outside/rinds of agates and t-eggs a LOT better than tin ox.
The wool felt only lasted a day. Since it was so wimpy, I sewed it on top of a Kingsley pad. Stitched around the outside edge. Right away, I noticed little round "wool bunnies" from the wool fuzz being shaved by the heavy nodules and weighted slabs. By morning, it had developed a big hole in the center and the rocks just laid it off to the edges of the pan. I had thought I might use some spray adhesive to hold it down, but I don't think it was robust/durable enough no matter how it was mounted. Ah well, another thing learned. Reckon I'll have to cruise the local carpetiers and hope for some low pile wool rug.
SicksIn Stones - Hey, that lap sounds interesting! I've certainly learned a LOT about repairing vibe laps with this old Lortone and could probably get 'er wigglin' again. If my e-mail is visible/findable here, please send drop me a line and we can talk about it, ok? c-ya, Rick
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