rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Oct 15, 2011 0:15:38 GMT -5
I've read here that it's not a good idea to use 60/90 SiO2 grit in a vibe lap. Problem is, if I use 120/220 or straight 220 grit, my t-eggs and agates don't seem to get flat even after multiple 12-16hr grinds. Always seems to be a low spot somewhere - usually on the edge - or a low side or a groove that I don't notice until after the polish phase. Not the greatest light on my back porch and the only time I have to look at them is after work when it's usually dark. My grinds all start at night - typically 11:00PM to as late as 1:00AM - and go at least until 8 to 10 the next evening. Takes a good bit of time fashioning little duct tape "girdles" for all of the ones that are too slope-sided for rubber bands to stay on.
When I first got my 20" Lortone working, I used 60/90 grit on a couple of batches and they all got good and flat. All my rocks get flattened out on a 100 grit spinning lap b4 they go to the pan. Ever since I quit the 60/90, my polished batches usually have a good 25-35% fallout and I end up having to stick the biggest rock I can fit on top of them and send them back to the first stage worried that the pattern I liked so much might get worn off.
So - Just exactly HOW BAD is 60/90 grit for your pan? Is it just a difference between a pan lasting 5 years and it only lasting 2? Or does it kill the pan after a few weeks? And what are the symptoms of a pan being worn out in the first place? Grooves? A hole? Or just really thin on the bottom? How long do grind pans usually last?
I've got a ton of rocks I want to polish - and life is short, lol. I run the pan pretty loaded - probably TOO loaded - but with as much space as they take up, I doubt any area of the pan will wear more or less than another. Though, maybe the outside, as it seems the larger rocks tend to gravitate (literally! lol) there after a while by shoving everybody out of their way. Thanks! Rick
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Post by johnjsgems on Oct 15, 2011 8:12:00 GMT -5
I can't answer the pan life question but have a better bumper idea. Use hose joined in circles around the rocks. They don't have to fit tight. I used braided hose called "Tygon" but any hose would work. I joined the ends with scrap stubs of copper tubing but a smaller hose that fits the ID would work as well. Make sure your pan is flat too. I think Lortone takes a long time to grind because of their plain pan without dimples or grid work to allow grit slurry to move under the rock. Maybe try less rocks at one time also. I hated the Lortone I had by the way.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Oct 15, 2011 12:18:08 GMT -5
Thanks - yeah, I bought some tubing last week and also some 1/8" aluminum tube to make connecting inserts.
I have a Lortone because that's what happened to pop up (very) used on ebay and I won at like $270. I've made some mods and repairs and it seems to work decent. Except for getting rocks flat when using the not-so-coarse grits I've seen recommended. I have an 8" Inland spinner lap that I try to get mst of the heavy work done on but, it's really hard to get a fair-sized slab or a thunder egg perfectly flat with one of those. The main reason I wanted a vibe lap was for the flatness.... and it does 15-20 rocks at one time.
You ended up answering a question I'd asked earlier in a different thread about the Lortone grind pan being flat. Do you reckon that, if I got one of the gridded bottom pans made by whatever other company it is, it would work on the Lortone base? Seems to me that, as long as it's the same OD as the pan I have now, that I should be able to just swap it in, right? I reckon I *could* just go for broke and use the 60/90 grit on this pan and then get a gridded one whenever this one wears out.
Haven't had an answer to that question yet but I'd imagine that *whatever* the signs or symptoms of a pan being worn out are, they should be pretty obvious whenever they appear, no? C-ya, Rick
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Post by jakesrocks on Oct 15, 2011 12:39:12 GMT -5
Rick, how thick is the bottom of your pan ? If it's thick enough, you could take it to a machine shop and have them true up the bottom and mill a criss-cross pattern in the bottom to help carry grit under your slabs.
Also, if your slabs are too light, they'll bounce around in the pan. You might have to add weight to the lighter ones. Don
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rockhound97058
freely admits to licking rocks
Thundereggs - Oregons Official State Rock!
Member since January 2006
Posts: 760
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Post by rockhound97058 on Oct 15, 2011 23:42:48 GMT -5
The Lortone pans on the 20" and are aluminum - so 60/90 will tear them up pretty quick. - My experience with 60/90 on the vibe-lap is it really undercuts certain stones - Thundereggs especially.
Did you happen to get a copy of the original instructions and parts list for this unit? If not shoot me your address via PM and I can mail you a copy. The papers I have come from the machine I have which is in the 70's? So of course the price's are a bit old - however it's great to show the parts breakdown and it also has the instructions for grit usage ect.... I never follow them, but it's good reading material.
The pans when they get worn usually dish out in the center - My Highland Park vibe-lap is getting worn and smaller material I don't see any problems, but large pieces you can tell as it leaves low spots in the center of the stone. - You could probably use a straight edge and place across the pan and see how dished it really is?
You mentioned the low spot on your stones your finding are on the edges? - I'm wondering if this is caused when you cut them and your blade first enters the stone and is rolling one edge? Or maybe - Unsure how you do it, but when the saw drops the cut piece it commonly leaves a little nub?
Happy Lapping!
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Oct 16, 2011 15:36:47 GMT -5
Thanks, Don - Hard to really tell just how thick my grind pan is. I bought it new a month or month and a half ago, so I reckon it isn't all that worn. Though some of the nodules I've had in it are pretty darn big. A couple of Ky. Agates - one about 8-9in across but only maybe 2.5in thick and another that's like 7in but is a good 5in deep. And a Black Rock t-egg that is about 6in across and 4in deep with hardly any slope. I'd had the same thought about machining the bottom. There's a machine shop where I work and I thought maybe they might be able to handle something this large. I googled around a bunch looking for anything with a 20" machined pan that I might buy an extra pan and stick onto my Lortone but all I found of that size was a "Reciprolap" and it *looks* like that one might have a pan that a machined plate goes into(?). Looks like that one has shallow, round holes in it and I'd also thought that maybe our machinist might ba able to do that if the grid was too difficult. Seems like the grid might work better than the "dimples", though, just from looking at it. Yeah, I figured out the weight bit pretty quick Though all I have right now are chunks of quartz/schist/feldspar from the Diamond Hill Mine in SC. or landscape "river rocks" to strap on top of them. Sometimes hard to get them to not be top heavy and flip. And really small t-eggs or agates with rounded tops are always an adventure - lol.
RH97058 - re: the manual - Ok, I'll figure out how to do the PM thing. Thanks!
As to the low spots. Most of what I've got was already cut. And they almost ALL - slabs, too - have that blasted "nub". Aaaarrrgh! It REALLY bugs the heck out of me, too, because you have to grind it off b4 you can even think about putting it into the pan. I hate that! And after you get it flat, there's almost always this deep, wide groove right before where the nub started and you have to lap for half an hour to get THAT manageable. My theory is that, right at the end of the cut when there's just a thin piece attaching the slab or nodule half to the clamped main rock, the loose slab vibrates or wiggles before it drops off and that this makes the blade wiggle. Not sure if I'm right about that. I'm slowly getting together metal scraps and odds and ends to build my own saw and my design for a vise should stabilize everything a lot better than any of the commercial ones I've seen. The rough I have I've been cutting on 10" and 18" Lortones at the local rock/gem club. On the bought rocks, the low spots that aren't from the nubs are small rounded places near the edges.
The low spots on what I've cut, myself, are mostly either from the 'nub" thing or sometimes right at the beginning of the cut where it seems like the blade started and then jogged over maybe .030". Seems to happen, mostly, on rocks with a very smooth rind and that are sharply sloped like end cuts or very irregular ones where the blade might have started on a pointy spot on the rock. The vise carriage on the 18" Lortone at the club has some wobble to it on the cross-feed. I showed it to the old(er) guy who maintains them but we couldn't figure out where an adjustment was for that so I *guessed* that maybe it was intentional to allow for if the vise feed wasn't absolutely, dead-nutz perpendicular. Maybe to let the vise float a bit to find it's "happy place"? Hard to see in down there, but maybe there isn't a big enough flange washer on the blade? The blade seems to have play in it, too.
Was going to start another thread but, since we got on this subject - I notice that agates many times have sorta *hidden* wide grooves across their faces. It *seems* like* these grooves don't show up until you start to lap the agates on a spinning 100 grit diamond disc to prepare them for going into the vibe pan. I could almost swear that they aren't visible/there until after you lap the slabs/nodules! Makes for a TON of spinner lap work/time wearing the rest of the rock down to smooth it out. The grooves seem to match the blade marks' pattern but they aren't there until you start grinding. Have you ever seen this? Could it be that maybe diamond is too hard to lap agates? Or from pressing too hard or not keeping the slab moving or it getting too hot? It doesn't happen all the time but enough to where I'm leery of grinding agates and, on my best ones, I just toss them into the vibe pan and repeat the 220 for as many times as it takes to smooth them out.
Oh yeah - the real subject - lol I reckon I'll have to just stick with 120/220 grit then or maybe graded 120 grit occasionally. I've tried using Zap-a-Gap CA glue (like Hot Stuff, I think) for rocks with softer bits in them like t-eggs. One, that I coated completely and thickly, turned out awesome. The other - thinly coated so glue wore off the harder areas - had no undercutting and was glass smooth but the moss ended up super shiny and stuck out because the Zap-a-Gap was so much shinier than the rest of the rhyolite of the t-egg. The glue soaks into softer moss or plume inclusions. I reckon this might be considered "cheating" by some pros, but I just want these all shined up for my own collections. Thanks, Rick
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Post by jakesrocks on Oct 16, 2011 15:56:32 GMT -5
Rick, another thing you can do to increase the amount of grit getting under your stone is grind a very slight bevel all the way around the piece. You don't have to grind much. Just enough to break that sharp edge around the rim of the rock. Those sharp edges actually push the grit away from the rock. Don
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rockhound97058
freely admits to licking rocks
Thundereggs - Oregons Official State Rock!
Member since January 2006
Posts: 760
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Post by rockhound97058 on Oct 16, 2011 19:26:31 GMT -5
Rick - Unsure about a source for a direct replacement for your Lortone lap - but your correct the rociprolap pans are all one piece machined with a large center bearing and a machined area that rides on nylon bushings. These units rotate while shaking - much different movement. The Lortone as you know is a single one piece aluminum pan such as a pie pan so to speak which sits inside another pan and is held with 3 thumb screws.
Jake - Good suggestion on the stones to bevel the edge - this is a old school trick and I do see people doing it, but die hard Thunderegg collectors such as myself shiver when we see it lol ;D
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Post by jakesrocks on Oct 16, 2011 20:11:54 GMT -5
Guess I'm just old school. LOL. Actually, by the time you're finished grinding and polishing an egg, you can barely see the bevel. The old spinning laps were much better at doing eggs and geodes than the shaky type laps are, but most people these days are too lazy to stand in front of a lap for hours moving your piece around the lap plate by hand. Wish I could find one of those old spinning laps in good shape.
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rockhound97058
freely admits to licking rocks
Thundereggs - Oregons Official State Rock!
Member since January 2006
Posts: 760
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Post by rockhound97058 on Oct 16, 2011 22:44:49 GMT -5
Very true - In my shop I use a combination of various machines to process my Thundereggs. Most commonly I use either a 20" flat lap (rotating) or a 20" Highland Park both with 120/220 grit to flatten out my stones. I then follow up with a Richardson's highspeed sander and finish with 600 grit on a expando drum. Polishing depending on what I'm doing is either hand polished on a leather wheel or a 20" Lortone Vibe-lap or the rociprolap depending on the size of stone I'm doing.
I know buddies of mine in the Europe market strictly use spinning laps to process their stones. Their material however is flat as a still pond, however the shine is a semi-gloss as I call it. I personally try to get as flat as possible, but it's not a priority I strive to achieve the best shine as possible.
I keep looking at the Ulitmate Grinder (or Bullwheel sold by Kingsley), just can't choke the price they want for it. I've thought about building one, however the issue with time to tackle a task is hard to find.
Anyrate I million ways to do it and they are all fun! I can never get enough - well maybe LOL when someone orders 300 cut and polished Thundereggs it gets old in a real hurry ;D
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Post by jakesrocks on Oct 16, 2011 22:55:42 GMT -5
One advantage to the old rotating flat laps. It's easy to adapt sphere cups to the spindle, and cut spheres the old school way. One cup and a leather glove.
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rockhound97058
freely admits to licking rocks
Thundereggs - Oregons Official State Rock!
Member since January 2006
Posts: 760
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Post by rockhound97058 on Oct 17, 2011 0:11:46 GMT -5
Interesting - never tried that! Howard Dolph used to use a electric motor with a single cup and cut garnet marbles from his star garnets.
All I've ever used is the 3 head machine I have. I keep thinking about building another machine and do some things different than the one I have.
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Post by jakesrocks on Oct 17, 2011 8:39:03 GMT -5
I had a friend years ago who had a home built 36" Rotating lap. He used to turn bowling ball sized spheres on that thing, using home built cutting cups made of plumbers bell reducers. Just the one cup, a water and grit drip, and to start out 2 gloved hands until he got the sphere ground round. Then it was all 1 hand. To keep things clean, he had separate cups and gloves for each grit. It was amazing how quick he could take a rough sphere all the way to a polished piece.
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Oct 19, 2011 17:37:37 GMT -5
".... grind a very slight bevel all the way around the piece...."
Thanks, Don - That makes a lot of sense. I did that for a while when I was trying to polish these rocks on a spinning lap so that the rock wouldn't dig into the felt pad and get yanked out of my hand. Recently, I was watching a video by Phil Stevenson on polishing Bruneau nodules with a wheel and he let drop a comment about how he found the beveled edges "unattractive" so, me being a rube/noob and all, I figured, "hmmm, maybe I shouldn't do that". I reckon it *does* look kinda funky if the bevel is really wide and deep but a slight one like you advise ought to really help.
In the meantime, to get a little more "wiggle to the jiggle" on my rig, I changed the balls from some approx. 3.5" rubber ones to some golf balls. I theorized that this would increase the travel by lowering the axis of the vibration and also by making the springs a bit looser. Seems to have helped some. The vibration is noticeably more vigorous and all of the rocks I ran for about 17 hours got flat... except for a couple of these darn Royal Sahara Jasper slabs that seem they'll take a dozen grinds to get all of the low spots out. And that's with some pretty hefty rocks strapped onto their backs, too. Might have to start getting a little picky about which ones I polish because they take up space in the pan and tick me off so much when they won't wear down.
I've started feeling out the machinist guys to see if they might mill a shallow grid into my pan. Does anyone have a ballpark idea of how deep the cuts are in those grind pans that have them? I'm guessing no more than like 20-30 thousandths. It would seem like, the deeper they are, the longer they'd last b4 the pan wore flat but, at some point, they could be too deep to where the grit can't escape them and it would take a good bit more grit per grind, too...(?)
C-ya, Rick
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Post by jakesrocks on Oct 19, 2011 18:01:19 GMT -5
My old Highland Park Vibro lap has the criss cross groves cut about 1/8" deep. The machine had barely been used when I bought it, so the pan is like new.
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rockhound97058
freely admits to licking rocks
Thundereggs - Oregons Official State Rock!
Member since January 2006
Posts: 760
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Post by rockhound97058 on Oct 19, 2011 21:14:42 GMT -5
I agree with Don - My HP Lap is also machined right at 1/8" deep.
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jimrbto
noticing nice landscape pebbles
Member since April 2007
Posts: 94
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Post by jimrbto on Oct 28, 2011 15:50:15 GMT -5
I was taught many years ago to never use mixed grits when lapping. Alway use straight graded grits. I learned the hard way (for me) to never start with anything coarser than 120 grit.
Your slab saw should have NO play in the vise or blade.
When starting a cut on a rounded smooth surface let the blade just "kiss" the rock to leave a mark, then take a flex shaft w/diamond bit and cut a small groove at that spot. Move the rock back to the blade and see that the blade engages the groove. Make the cut very slowly and advance the cut until the blade is in to the depth of the diamond rim of the blade. Cut slowly! ! ! Speed is wasteful, always. Grooves,blade arc, in the cut surface of an agate were put there by someone, they can't just appear. When preparing slabs for lapping, grind a very shallow 45 degree bevel all around the stone, this will allow the grit to get under the stone to do its job. The deep grooves in some slabs is caused by allowing the stone to stop with the blade still running, there is no such thing as a perfect blade and all have a little "wiggle" and that wiggle will cut a groove as soon as the rock stops. Nubs at the end of a cut are (for me) impossible to avoid. I can keep the nubs quite small by finishing a cut feeding by hand very slowly. Adding grooves or dimples to a lap plate increases its cutting efficiency and my Rose "Rociprolap" is due for a visit to Covington to get a new surface. It is badly dished (a gift) and can no longer cut a large slab. Jim
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rykk
spending too much on rocks
Member since September 2011
Posts: 428
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Post by rykk on Oct 31, 2011 0:41:24 GMT -5
"...I learned the hard way (for me) to never start with anything coarser than 120 grit..."
That's what I use, now. I did use 60/90 on maybe 3 batches in the very beginning. It's what I had around and was used to from tumbling and I didn't think about pan wear until reading about it here. Was just hoping it was something you could get away with - impatience!
"...Your slab saw should have NO play in the vise or blade..."
Yeah, I pretty much didn't think it should. I'd pointed it out to the guy who maintains the saws at the club but he couldn't figure how to adjust the play out of the vise carriage. On both their 18" and 10" Lortones, the blades also move a LOT side to side when you press on them. I can't see inside but wonder if the flange washers are either too small or are somehow bent out of whack. I don't reckon the play would be from the blades being loose or they would bind as soon as the feed brought the rock into contact(?). I'm gathering stuff to build my own saw soon. Just need to talk the machinist at work into fabricating one of those sorta "L" shaped pieces that fit into notches in the vise base and that tighten the clamp. At least that's how these Lortones are set up and it seems pretty good. I have designed a vise system that should keep the "nubs" from happening... if it works - lol.
The saws the club has were donated and I guess they're pretty old. The big one has a real bad habit of "walking" on you, especially on thin cuts. I spent almost 2 hours today trying to smooth out an 8" Teepee Canyon agate slab but am still looking at either 4-6 "wiggles" with 120 grit or a lot of hours on a spinner lap with a 100 grit disk because the middle is a good 30-50 thou high still. Really bugs me because I saw a slab like it at ebay but it sold for like $193 so this chunk was/is my only chance to have one like that unless I get really lucky sometime.
The 10" saw's feed seems uneven, which may be why there are wide, shallow grooves in some of the rocks I've cut on it. They're a real "she--nine" to grind out and sometimes it loses you the pattern you liked. It has a couple of threaded brass blocks that clamp down onto a threaded rod for the feed. The rod seems like it wobbles slowly where it's attached to the end of the pin that drives it. You can hear it in the sound of the cut. These are my only real options right now. The home-built saw will happen like that sort of thing usually does... someday... when work isn't too demanding... when I have time...lol.
I've been, lately, sort of doing what you suggested as far as starting the cut. what I do is either put my finger or hold a piece of wood on the side of the 10" blade (18"-er is under a cover and slings lots of oil) for the first bit of a cut so that it doesn't walk to one side and then let it go once it gets seated.
I have a few more batches of 600 grit with one or two batches of 220 grit "re-grind" slackers to do and then I can switch to the polish pan. That'll take a good few days, so maybe I can get our machinist to either mill a grid or just end mill a pattern of dimples. BTW - about what is the diameter of the dimples in your Reciprolap? I'm guessing 1/4" dimples 1/8" deep would be pretty close? For that matter, I could probably rough out the job by myself close enough to work using a hand drill, ya think? Thanks a TON for all the tips y'all, Rick
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rockhound97058
freely admits to licking rocks
Thundereggs - Oregons Official State Rock!
Member since January 2006
Posts: 760
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Post by rockhound97058 on Oct 31, 2011 9:08:31 GMT -5
Hey Rick - The rocipro dimples are - 3/8 to 1/2" in diameter I'm guessing and maybe 3/16" deep. That's just off my head... I'll be working at my shop today, so I'll measure it for you.
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