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January 21, 2019, 09:33:26 am
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Carving Query

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Author Topic: Carving Query  (Read 359 times)
stonemon
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« on: October 24, 2015, 03:30:45 pm »

I would like to carve and polish a concave symmetrical bowl about 1 1/2" wide at the surface and 3/4" deep in a Welsh agate nodule. 
Any thoughts or advice on this?
I am trying to avoid my Rube Goldberg tendencies!
Thanks for your input.
Bill
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Debbie K
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« Reply #1 on: October 24, 2015, 05:49:47 pm »

Bill:

First: Where are you located? If you are in the States, you will definitely find this to be useful. http://www.harborfreight.com/large-diamond-rotary-grinding-wheel-set-4-pc-69658.html

Second: Do you have a rock grinder? If you do, all you'll need is this http://www.kingsleynorth.com/skshop/product.php?id=95058&catID=567 or one of these http://www.kingsleynorth.com/skshop/product.php?id=92031&catID=333and the burs above and some that you make.

I made a Turkish jadeite cup, 2.5" wide by 1" deep, and a blue chalcedony cup with these and other tools. I bought an arbor from Kingsley North that cost about $50; I just looked on their website but didn't find it. I inadvertently threw away their catalog; I'll keep looking.

Now, to polish I used hobby shop 1.5" maple balls. I drilled a 1/8" hole thru them and then a bigger hole large enough to accommodate the screw on top of the arbor that I mounted them on. I used oil and diamond grit and these balls to polish them. My progression was 100, 200, 600, 1200, 3000 and 8000. I advise making on extra ball as the 100 and 200 wear down so much. You could just as easily use those hobby wooden wheels to polish the inside of your cup.

I used a rock grinder on the outside.

Debbie K

P.S. I meant to mention that some folks use modified drill presses with the chucks and a drip. You can use it like a lathe also, and grind down your rock until you're able to chuck it, and use diamond files to shape the outside.


* arbor.jpg (106.62 KB, 2272x1704 - viewed 6 times.)

* 600-grit.jpg (88.21 KB, 1704x2272 - viewed 8 times.)

* IMG_2097.jpg (822.15 KB, 960x1280 - viewed 6 times.)
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stonemon
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« Reply #2 on: October 24, 2015, 06:21:42 pm »

Great info Debbie.
I am out here in western Oregon and have a harbor freight just 50 miles west.
A couple questions;
What kind of rock grinder are you referring to?  Dremel type?
Did you free hand the initial cut on bowl?
Was the whole process done with your hands involved or were some of the steps longer.
Thanks for the info.
Bill

 
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Debbie K
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« Reply #3 on: October 24, 2015, 07:34:14 pm »

Bill:

I have an old cabbing/grinding unit, kinda like a Lortone, with two hard diamond wheels, an expando wheel and saw. I freehanded the outside shape on my cabbing unit, and used the arbor I built as a point carver. I tried to "Goldberg" something first, but it was too dang dangerous. All of these large bits weigh a lot, even the wood ones, and the thought of something like that coming loose and hitting me in the face was too scary even for me.

Once I had the outside shape, I carved out the inside with the "wheel" shaped diamond grinder. I crisscross cut the interior, and when it was sort of evenly cut I began to spin it. I just held it tightly in my hands. The blue chalcedony one got thrown across the room on the last polish, 8000 grit, and I nearly cried. It was so much prettier than the lavender jade and had gorgeous translucency. Needless to say, it broke.

A Dremel or Foredom would take a really long time to carve away a lot of rock on the outside. I'd recommend making some sort or arbor and buying the chuck and maybe a large diamond bit or small wheel from Jade Carver. Silicon carbide stones work, but they're very slow. Just checked their website and catalog, doesn't look like they carry the type of bit I have on my arbor that's shown in the picture I posted previously. But they do has this. Scroll down to the second group of bits and you'll see what that might be perfect for the inside of your bowl; cost more but might be worth it. http://jadecarver.com/DiamondTools.htm

I forgot to mention, before I started sanding the inside, I used a large silicon carbide ball bit to smooth out the grind marks. And also forget to mention, you must use water to carve. I use this drip system with both my point carvers.

Debbie K



* point-carver.jpg (11.41 KB, 480x640 - viewed 6 times.)
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Debbie K
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« Reply #4 on: October 24, 2015, 07:45:42 pm »

The last picture shows the harbor freight bit in the flexible shaft.

Important safety tip:
Although I was able to chuck and rotate this bit with a Wecheer flex shaft, the sheer weight of the bit loosens the tightening mechanism inside the handpiece. It would come loose while it was running. This is why I built the other one with a real Jacob's chuck. I was having to hold the bit in place with the rock until the motor wound down, and since it has a 1/2 hp motor, it seemed like an eternity.

Debbie
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stonemon
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« Reply #5 on: October 24, 2015, 07:52:40 pm »

Got it!
I have a couple of cabbing units, the outside is not an issue.
I will go look at what diameter wheels I can get my hands on. I understand about the water and am thinking about how to do that piece.
Thanks again for the advise. And the safety tip....!
Best,
Bill
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slabbercabber
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« Reply #6 on: October 25, 2015, 05:07:34 am »


This is not something I have done exactly, but if I were doing it, I would start with the inside first and then mount the cup on a ball centered on a turntable to do the outside.
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« Reply #7 on: October 26, 2015, 09:31:16 am »

I purchased a large number of unfinished bowls from an estate.  These were initially cut by Dr. Hilquist in the late 70s and 80's.  His method of cutting the bowls was to obtain stainless steel ladles, cut off the handles and solder on a edge of a saw blade that he cut off from a standard notched rim blade.  He would then start cutting out the bowl with the block locked in place and the ladle cup rotating and being slowly tilted into the stone.  Using different size ladles, he was able to cut bowls up to 6" in diameter.

For polishing, he mounted the bowls in plaster of paris and used a homemade flex haft with custom made polishing heads to sand and polish the interior and the reversed to polish the exterior.  I currently have about 90 bowls to work on in my spare time of which I have none.  I have a lot of brazilian agate, tiger eye and a few of dinosaur bone, Creede amethyst agate, and Biggs jasper and jade. 

I just need to work out the the best method for me to finish the interiors.  Thanks for all the ideas in this thread


Bob Johannes
The Amethyst Rose

come see us at the Agate Expo 2016 in Cedarburg, Wisconsin
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stonemon
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« Reply #8 on: October 26, 2015, 10:07:20 am »

Sounds like a lot of work Bob!
I found this site yesterday, ball burrs up to 50mm for what seems a very reasonable cost.
http://www.eternaltools.com/burrs/diamond-ball-burrs
I ordered a 30 and a 40 mm for my project and will hit the craft store today when I drive into Eugene to pick up some wooden balls for the polish... We will see.
Thanks to all again for the nudge.
Bill
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Amethyst Rose
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« Reply #9 on: October 26, 2015, 01:26:55 pm »

Those burrs look interesting.  I was thinking of trying out the 3M bristle brushes.  They make ones up to a 3" diameter which would work well in my carving arbor.  Only issue I see is the longevity as they are silicon carbide rather than diamond but they come in a vast array of grit sizes.  Just need the time and money to get too it.  Right now, just overly busy cutting stones for the fall show season and for next year's Agate Expo. 

Bob Johannes
The Amethyst Rose
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Debbie K
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« Reply #10 on: October 26, 2015, 07:01:35 pm »

Harold Van Pelt http://www.bing.com/images/search?q=harold+van+pelt+gemstone+carvings&FORM=HDRSC2 uses a lathe to turn his vessels. I used to have a tutorial on his process, but I can't locate it. I believe he used diamond files to shape the outside.

If I remember correctly, he used core drills and drilled multiple holes and then broke the rock loose from the interior with pieces of steel.

It is interesting to look at his pieces, they're not absolutely perfect. Sometimes the rock stops you from doing what you think you want to do, and it was evident in one or two of his works. There was an amethyst glass in particular that I remember, and the lower side of it was unpolished. When you looked closely you could see why; it had developed a stress crack. It was nice, in a way, to see that he had the same problems that all of us do when working with rocks.

Debbie K
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« Reply #11 on: October 26, 2015, 08:03:10 pm »

John Sinkankas described both a method for creating a bowl-shape and a machine for grinding/polishing it in my second edition of his "Gem Cutting: a Lapidary's Manual."  For hollowing he suggested making numerous cuts to the same depth with a diamond saw blade of the desired radius then breaking solid pieces free by wedging.

The polishing machine involves two electric motors, one operating at a very slow speed to rotate the work piece during grinding; the second working at a presumed 1725 rpm to run a shaft-mounted grinding wheel angled to smooth and polish the bowl's interior.  The grinding shaft can be lifted to change wheels, add grits or whatever.  His design used silicon carbide grinding wheels which were worn down by use to the bowl's interior radius.  He wrote that the machine could also be used to shape and polish the bowl's exterior but the explanation exceeded my limited mechanical understanding but should be easily-understood by the mechanically-inclined here. 

Anyhow it's a system similar to the one I've read is used in Idar-Obertsein, Germany, where agate/jasper bowl-making has a 200-year history.
 

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