jamesp
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Post by jamesp on Oct 11, 2014 8:03:16 GMT -5
I know glass makers remove grind marks with a torch to give a super 'hot shine'. That's another story. Would a tumbler do a Beilby shine ? I doubt it. Beilby used the term "melt," but it is really "crystallizing," molecules electromagnetically moving from a high spot to a low spot. Friction on a buff somehow produces it. I have a friend that bought oversea containers of Brazilian agate. He would go to Brazil and pick from the various suppliers. They shipped them back in 55 gallon drums, mostly full of slabs. ave weight 660 pounds. Back 15 years ago they were $2.50 - $3.00/pound, mirror polished both sides. He said they had a diamond belt about 6 feet long, about a foot wide laid flat and rolling fast. That they did a one step polish right off the saw. He said they wet their fingers and flipped the slab on to the belt. Moving the slab in an orbital motion with their fingers. And before the heat got to intense they slid it off the edge and into their lap. Picked a cold slab while the hot slab cooled and kept going. It makes sense, how could they polish that many slabs and sell that cheap?? No way they used a lap. Howard is up in Indiana, I need to call him and get details on that belt operation. If you look at the polish on their slabs they look almost molten as if flame polished. Dave1 mentioned the Beilby effect: Sir George Beilby (17 November 1850 – 1 August 1924) discovered that during polishing the surface of gemstones actually melted and flowed as a “glassy” layer over very fine scratches. He proved it by noting a certain scratch pattern, polishing the surface, and then recovering the scratch pattern by etching away the polished surface with acids." Well. if you have a belt that long coated in fine diamonds it would stay cool and last a long time. It would stay cool but the slab would sure get hot at high belt speed. Like a buffing pad. And cool diamonds could remove a lot of saw scratches even if it was a polish grade. Read more: forum.rocktumblinghobby.com/thread/67973/polish?page=6#ixzz3FqCoFh1e
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Post by mohs on Oct 11, 2014 8:54:42 GMT -5
real interesting
what if someone came up with a method to tumble w/ heat? It have to be a controlled heat and agates only but that may emulate the Beilby effect and quick polishing
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jamesp
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Post by jamesp on Oct 11, 2014 10:05:22 GMT -5
real interesting what if someone came up with a method to tumble w/ heat? It have to be a controlled heat and agates only but that may emulate the Beilby effect and quick polishing I had a PVC barrel get stuck on a shaft and rubbed a bump in it Ed. After freeing it it formed a bunch more bumps like the cups in a tire. They propagated all the way around the barrel. It rotated with a serious vibration. Not a problem but a bit noisy. It made me wonder what was going on inside the barrel. I finally took an angle grinder and ground all the high spots off. But I think there is merit to a bumpy barrel. If you do the hertz: 22 inch circumference on a 6 inch PVC. 1.5 inches per bump = 14 bumps/reyolution at 60 RPM=840 vibrations per minute. That works out to 1.2 million shakes a day. More shaking than I want to do. That's a whole lot of shaking goin on. Was that Jerry Lee Lewis or Elvis ?? I think vibs are 1000 to 1725 RPM motors w/a counterweight on the shaft making 1000-1725 vibrations per minute. Much faster. Maybe heated shafts would get a hot tumble...
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Post by mohs on Oct 11, 2014 10:51:29 GMT -5
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Post by mohs on Oct 11, 2014 10:56:33 GMT -5
I like the hot rods in the barrel grind'n & a shinin' just won't stall
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jamesp
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Post by jamesp on Oct 12, 2014 5:57:26 GMT -5
Did a test on grit and two rocks and figured out why the wear profile in a rotary tumbler is frosted. I pulled two fairly rounded rocks out of the barrel and wetted them with slurry. Sprinkled them with AO 220 and rubbed them together lightly. I am certain that the grit rolls. It does not seem to slide. If the grit is washed off, and the rocks are rubbed together, rock to rock contact occurs, and more friction occurs. The grit is behaving like small ball bearings. With teeth or fine sharp points to grab, roll and abrade. The grit appears to be constantly rolling, like marbles between two boards. The grit is graded through a screen and rounder particles are sought after in process as opposed to flat particles. Assisting in the rolling behavior. Test can be simulated w/a piece of paper and salt. Poor tiny bit of salt on the table and lay a piece of heavy paper like an index card on it. Rub the paper in circular pattern on the square salt particles with light pressure.. You can feel the rolling action. Even though the salt is squarish in shape. Then rub the paper on the clean table. It drags more. Some photos were taken to look at a frost pattern on hard agate. Not the best example since they are in AO 1000 stage. Better to take photos of agate in 30,90 or 220 grit for magnification purposes. But using strong sun light they did OK. Actual size, piece of lavic siding jasper: Blown up w/software 3.3 X magnification: Closer macro of coral, actual size: This time blown up 14 X magnification. Problem with coral is the crazy polyp fingerprint. But fine satin frost apparent in the solid material between the patterns: This is botryoidal fill with out the coral fingerprints, strong sun light, actual size, satin haze evident: Same stone, closer in, best example due to strong light: And back to the obsidian, 220 grit, linear scratch free, just frosted:
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Post by mohs on Oct 12, 2014 9:18:20 GMT -5
excellent detective work James! this all goes back to grit structure profile
so as a general rule: grit that slides=good for roughing grit that rolls=better for polishing
would you agree in theory ?
fabulous pictures !
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Post by mohs on Oct 12, 2014 9:22:05 GMT -5
that botryoidal as a rock'n heart trying to morph very cool
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jamesp
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Post by jamesp on Oct 12, 2014 9:58:53 GMT -5
The grit seems to roll in all stages Ed. This has been in 30 grit. Seems pitted in the photo, frosted to naked eye.
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Post by mohs on Oct 12, 2014 10:31:10 GMT -5
I see roll & abrade interesting
I’m trying to imagine this action on grinding wheel especially sintered diamond wheel
most people notice a real aggressive action on new sintered diamond wheels. I wonder if this is because the fresh points of the diamond are doing a sliding action? Then after use this aggressiveness diminishes . Perhaps the points have rounded over and more of a rolling action occurs?
Seems like sliding is good for roughing and rounded is better suited for polishing
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Post by mohs on Oct 12, 2014 10:34:40 GMT -5
James
do you know how a sintered diamond wheel is made?
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Post by captbob on Oct 12, 2014 10:37:39 GMT -5
'nuther question while you're answering.
How noisy is your tumbler? Rocks crashing or more like rolling in the surf?
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jamesp
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Post by jamesp on Oct 12, 2014 12:33:58 GMT -5
'nuther question while you're answering. How noisy is your tumbler? Rocks crashing or more like rolling in the surf? I got several speeds captbob. All 6 inch barrels. 12,24,30 and 60 RPM. 12 and 24 and 30 are pretty quiet because they are for finishing grits with barrel like 3/4 full and thick sugar slurry. The 60 RPM is usually 2/3 full with no sugar and is loud for touch rocks like coral and agates for early in the coarse grind, then 3/4 full for later in the coarse grind. The tumbler can rotate 12 and 30 or 24 and 60 depending on which motor pulley is used. It has one motor but 2 sets of shafts.
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jamesp
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Post by jamesp on Oct 12, 2014 12:44:59 GMT -5
James do you know how a sintered diamond wheel is made? Ed, grinding wheels and sintered wheels scratch, the abrasives are bonded to the wheel. Loose powdered grit often rolls. The Chinese are making all kinds of sintered metal to hold diamonds. I think it has copper in it. I think other metals that can be silver soldered. But do not know how they make them. it will not surprise me if they start making solid sintered wheels for a 6 inch bench grinder. How to dress an out of round sintered diamond wheel ? I think this is for a bonded diamond wheel and not a sintered wheel:
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Post by mohs on Oct 12, 2014 13:24:33 GMT -5
right on James !
I used to construct wood cutting saw blades by brazing carbide teeth to the saw seat. I’m must have brazed over a million teeth to saw blanks.
To grind all those carbide teeth we used diamond wheels of course. The diamonds in those wheels were imbedded into some type of adhesive.
I haven’t inspected my sintered Galaxy wheel closely. Wondering if the metal is melted & the diamond grit is pressurized into that flow?
Abrasive technology is intense...
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Post by mohs on Oct 12, 2014 13:26:35 GMT -5
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jamesp
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Post by jamesp on Oct 12, 2014 13:40:23 GMT -5
Rotary tumbler inspection after 6 days at 60 RPM using 30 grit. Clean black tub Pour contents from barrel, spray rocks with water, and let settle for at least 10 minutes Put rocks back in barrel and pour liquid back in With gentle spray inspect condition of grit settled on bottom of tub Close inspection shows grit broken down entirely. Probably 500 or smaller. Sprinkled unused 30 grit particles on top to see comparison. So useless for coarse grinding unless you have a whole lot of time. Had there been any large grit it would have stayed on the bottom of the tub as the water was poured off.
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tkvancil
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Post by tkvancil on Oct 12, 2014 13:44:02 GMT -5
And here I thought I was the only one doing that pour off inspection ....
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jamesp
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Post by jamesp on Oct 12, 2014 14:00:22 GMT -5
right on James ! I used to construct wood cutting saw blades by brazing carbide teeth to the saw seat. I’m must have brazed over a million teeth to saw blanks. To grind all those carbide teeth we used diamond wheels of course. The diamonds in those wheels were imbedded into some type of adhesive. I haven’t inspected my sintered Galaxy wheel closely. Wondering if the metal is melted & the diamond grit is pressurized into that flow? Abrasive technology is intense... That is a mean Frisbee Ed. Sounds like you are a master brazer too. Hey, sharpening carbide can't be kid play. I think the use EDM process Ed. Which is sorta over my head. Here is how they true a sintered diamond wheel using EDM: The application of cylindrical wire Electrical Discharge Machining (EDM) for profile truing of metal bond diamond wheels is presented. Instead of using the mechanical force to break the diamond and matrix in the grinding wheel, the wire EDM process uses the thermal energy or electrical sparks between the wire and rotating grinding wheel to remove the metal bond and form the wheel. The design and manufacture of a corrosion-resistant, precise spindle with the high-electrical current capability for wire EDM truing of grinding wheel is first introduced. Three truing configurations were designed to study effects of wire EDM process parameters and to investigate the level of form accuracy and corner radii achievable by the wire EDM truing of diamond wheels. Results show that the wire EDM process can efficiently generate the μm-scale precision form on the diamond wheels. The wheel, after truing, was used to grind the silicon nitride workpiece. Grinding forces and wheel wear rate were measured. In the beginning of the grinding, high wheel wear rate was identified. The subsequent wheel wear rate was considerably lower and stabilized. I had a slight headache after reading that one.
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jamesp
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Post by jamesp on Oct 12, 2014 14:07:47 GMT -5
And here I thought I was the only one doing that pour off inspection .... Grit is too expensive not to use it up. Electricity too expensive to waste on worn out grit. Same tumbler, same wear rate, same stones, repetitive process, pretty sure grit is shot after X days. But anything new gets the ole inspecto.
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