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Shaping and beveling very low domed cabochon

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Taogem
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« on: July 09, 2009, 11:34:39 pm »

After uploading the videos, realized that the audio on most did not pick up my voice. So will type out as best I can a description of what is going on in each video. I can hear them much better using my headphones.

I think could have slowed down a bit too and explained better and in more detail.. So parts of this may just be difficult to make heads or tails out of..

As always, what works best for me can be different for someone else. So please critique, add too, point out, or anything else that you find works for you so it can be added here for others to take in.

A lot of this really applies to most any cabbing.

One of the first things I like to take the rough edge off the perimeter of the preform.. I take it down through the 400 diamond bonded wheel. I don't want to be grinding on it later after I have my doming complete because it will result in changing the girdle height. So all I really want to have to do is touch it up with the silicon carbide stages.

Ok here we go.... !  :)

This first clip shows the grinding down of a bevel. Not a finish bevel. A bevel that will determine the girdle height and also the outside/lowest part of the low dome. Depending on the size of the cab or rather the surface area will depend on how little you will need to bevel. You can get away with a lot less of a bevel because no need for as much doming. A larger surface area will require more.. Make sense ??

No need to actually go though any additional beveling steps for the corners. The bevel from doing the sides will join nicely at the corners.



Here are a couple of pics showing the results. I leave the corners sharp cornered until the very end of the cabbing. Then I will round them off. If for some reason I want the cab to wind up with sharp corners, then I have to pay extra close attention to them as shown a bit later.



This next clip try's to show how to begin getting the contour of the dome uniform across the entire surface.

A while back someone mentioned how they listened to the grinding. As what ever grit your working progressively removes bumps and ridges the grinding sound will subside into a smooth almost quiet grinding action. Meaning the surface is uniform so to speak with the flat surface of the grinding wheel. So I work each wheel until I can go around the entire surface of the stone to the point where there is really no grinding going on.  Hard to explain. Just think about it while your working the surface of the cab. It will come to you !

I noticed that it appears in the clip that I am pressing harder than I actually am.. I am hardly pressing at all and the wheels are running a lot faster than these videos depict.. Just a video thing I guess..

I have come off the initial 80 grit and this step is on the 220, then moving on to a somewhat worn 220.

Again, mostly working the outer part of the surface of the cab and spending little time hitting the inner part or highest part of the dome. Don't want to grind down what little dome we are working to have in the end. Although I do have to spend a bit of time on the center just so as to include it in the grit processes. Most of the grinding is needed around the outer part of the cab. That is where the ridges were left which is more covered in the adjacent clip..

I notice too that my camera crew did not do a great job of showing a lot of the cabbing action.. Hopefully you will get the idea.

 

This next clip starts out going through the same process except on a 400 grit. Again, listening to the sound of the grinding.. Just like any other progressive grinding or sanding steps.. Need to work it until the previous abrasives grit marks are removed. Pressing fairly lightly.

The pic below shows a close up of the problem I run into on the corners.. The accidental excess grinding on them.





This next one shows how sometimes I have to go back over the girdle so as to keep it uniform. Sometimes as a result of going through the grinding process the girdle will become thicker in the center and have to re-bevel and then smooth out the surface a bit. Again.. A bit hard to explain.. Sorry. !



Next I move on to some silicon carbide papers. I start off on the 80 with this agate. Running up through the 220, 400, 600 and finally a worn 600 just like any other hard mineral cab. Other softer minerals, I may skip the 80 and start off with the 220.

I listen to the sanding just like I do the grinding..

You can see I have not tried Old Hickory's belt slipping trick yet.. !



This next one shows rounding the corners.



Finally..., Lets try beveling !



After going through all the silicon carbide grits for the bevel and girdle, here are the results !  :)















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Bluesssman
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« Reply #1 on: July 10, 2009, 09:10:52 am »

Fantastic tutorial, George! Showing each step as intricately as you have, will really help everyone wanting to do this work...


Gary
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« Reply #2 on: July 10, 2009, 05:01:18 pm »

  that's a great cab George! and a informative video...wow...I'm so used to my flat lap that this all looks foreign..and the beveled edge is pretty bas a**!  I've tried but haven't been able to do it yet  :'(
    You have a steady hand =)   
 
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« Reply #3 on: July 10, 2009, 06:31:51 pm »

I'm so used to my flat lap that this all looks foreign
 

I know what you mean... From my perspective set ups like cabbing with a flat lap is completely foreign to me.. Yet your cabs are awesome.. !

 

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« Reply #4 on: July 12, 2009, 11:38:57 am »

Thanks, Oh cabbing guru!! I have been watching the videos and taking in all you wrote. I am going to try your techniques maybe tomorrow. I am very excited to get started. Eric.  Again, thank for your time and effort!
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Bluesssman
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« Reply #5 on: July 12, 2009, 04:31:12 pm »

Eric, don't forget to take photos and share them with us!!!!



Gary
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« Reply #6 on: July 12, 2009, 10:02:12 pm »

Nice demos!

After spending a week teaching high-dome cabs, it's nice to see someone emphasizing NOT cutting the top of the stone right away even in a low dome cab. I had all the students draw small bull-eyes on the very center top of the cabs and told them not to touch that area until virtually all other work on the stone was complete on the 80-100 grit wheel.

It only takes about two or three passes to bring the stone into a nice dome if all else is done.

Here are couple example stones I used in the class:
A stone with both a hard and soft material side by side - a little test of cutting two different materials and maintaining an even look ... sonora sunrise - black jade


So what do you do with small cut-offs and scraps - glue them up together and form a multi-part composite


Finally when I had a little time to experiment, I tried to use the 6" Genie wheel shape to make a rounded frame and cut a center to match. THis stone domes on both sides. Not bad for a first try!


One more 1/2 done cab to show them how to maintain a high dome without destroying it. Keep the bulls-eye on top until all else is done!






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Taogem
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« Reply #7 on: July 12, 2009, 10:27:09 pm »

The drawing of the bull eyes is a great idea  !  Thanks for adding it here Ron ..   :)

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« Reply #8 on: July 29, 2009, 07:24:35 pm »

Great tutorial, have trouble figuring how to low dome plumed agate. The bullseye, on a high dome, is a great idea, have been using crosshairs along the two axis, but think the bullseye would especially work great on freeform cabs.

Dave
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« Reply #9 on: January 17, 2010, 12:14:22 am »

George, great presentation!  I will try the bezel at the end, I sometimes try to incorporate it near the beginning.  Again thanks for the tutorial.

Brad
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« Reply #10 on: January 22, 2010, 04:21:17 pm »

Was wondering, if the belts and the softer backing, help getting the low dome? The Genie's wheels just don't have a lot of give, but I almost think the Nova wheels are getting a small concave shape, in the middle.
(Can't always remember if it is concave or convex, have to always remember about the cave part. Kind of like stalactites and stalagmites, the stalactites stick tight to the ceiling!)
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« Reply #11 on: January 22, 2010, 04:27:54 pm »

Was wondering, if the belts and the softer backing, help getting the low dome? The Genie's wheels just don't have a lot of give.

No... The belts are used like normal.. Working out the abrasive marks from the diamond wheels.. Nothing to do with shaping the low dome.  Although with softer materials the heavier grit belts will take a bit more off the top than you may want.. Gotta be a bit careful..  :)

Funny you brought up the Genie's wheels not having the give.. I have asked about this myself in the past on here, and am assured that it is a matter of just getting use to them.

I keep looking at the Cab King unit.. Would mean I would be really taking a chance on getting use to the harder wheels.  Selling off what little equipment I have been using to partially pay for it..

I don't really know if I can ever see myself completely getting away from having a few expando drums with silicon carbide abrasives on them..

I really have become use to the softer rubber backing..

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« Reply #12 on: January 22, 2010, 04:52:12 pm »

Being heavy handed, I have really had to learn to be light on the nova wheels. Have been considering getting an arbor, for a couple of expandos, or something with rubber backings. Don't really know where to start, on what I would be satisfied with.
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« Reply #13 on: January 22, 2010, 04:57:05 pm »

Being heavy handed, I have really had to learn to be light on the nova wheels. Have been considering getting an arbor, for a couple of expandos, or something with rubber backings. Don't really know where to start, on what I would be satisfied with.

I really like the polly type arbors... I wish I had a couple more..

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« Reply #14 on: January 22, 2010, 05:00:20 pm »

Think I have asked this before. Polly arbor, brand or type? And what are the best type of wheels, backed with rubber?
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« Reply #15 on: January 22, 2010, 05:26:36 pm »

Polly is the brand..

The rubber that makes up these expando drums (below) is what allows for a little give when pressing against the belts.

If you go with these, you will want to go with the standard 3" x 8" ..

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« Reply #16 on: January 22, 2010, 06:39:50 pm »

I have a Genie and a Pixie and the Nova wheels on my Genie have very little give but the Novas on my Pixie flex and comform to my stone quite well. I perfer cutting opals and softer materials on my Pixie because of this  and also because my Pixie runs slower even though the wheels are smaller.
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« Reply #17 on: January 22, 2010, 06:54:55 pm »

Thanks George. Part of what I have been considering, is that I can get a pad that fits, our 8" Ameritool flat lap. Would have to get more plates and disks. Will probably talk to the owner, if he is in Kansas City, this March. And like Christopher, I like a slower speed for some stones.
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« Reply #18 on: August 15, 2010, 05:26:48 pm »

Thanks for all this good information!  Wish I had found it months ago but it's good to know that I have already learned some of what you are showing here.  Trial & error, just doing it, work great every time!
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« Reply #19 on: July 22, 2011, 07:21:21 pm »

Love the videos George - they were really helpful to me yesterday trying to figure out how to best hold the stone for a low dome. I love setting low-dome cabs so they're what I'll primarily be trying to cut!
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« Reply #20 on: July 22, 2011, 08:14:15 pm »

Love the videos George - they were really helpful to me yesterday trying to figure out how to best hold the stone for a low dome. I love setting low-dome cabs so they're what I'll primarily be trying to cut!

Excellent !

Let us know how you make out... !
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Eu_citzen
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« Reply #21 on: January 16, 2013, 12:06:35 pm »

Nice demo, I would like to hear your views on this.
I see that the edges are not rounded on this cabb on the demo.
I.e. there is a sharp corner between the bevel and the flat-top.

Don't you think it would be better to round of that as during wearing it may wear faster then the rest of the cabb? I'd like to think so. dunno
(depends on what kind of jewellery/setting etc, I know just thinking out loud)

Click on the thumbnail for a larger view, below is how I like to do my flat-top cabbs.
I do the approx same sequence just round of that bevel somewhat.



Just a thought.
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anthonyroman
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« Reply #22 on: May 05, 2014, 12:06:45 pm »

I like the first one. Its simple, unique and elegant! The pattern looks like a tree in autumn which is really cool. Great work!
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