January 24 Through February 4—TUCSON, ARIZONA: Annual show
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Fri Mar 29, 2024 1:02 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 64 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next
Author Message
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Sun Aug 14, 2022 6:08 pm 
Offline
Platinum Member
User avatar

Joined: Wed Mar 15, 2006 5:10 pm
Posts: 2117
Location: Maryland
1bwana1 wrote:
Precision Gem wrote:
1bwana1 wrote:
You give me cube shaped (which is a square in all directions) and I should be able to get very close to a 50% recovery in a SRB cut round. More if you don't need a standard brilliant cut.

What is called a "sawable" in Diamond rough is just such a shape, and that kind of recovery is commonly achieved on such rough shapes.


I'll take you up on that. Email me your address, and I'll ship you cube to cut.

If you look on GemCut Studio, the program starts out with a cube with a volume of 1. Make a SRB and then check the volume and it's around 0.22 So that's 22% yield.


Try this:

Don't place the table on one of the existing flat surfaces of the cube as you probably did in Gem Cut Studio. Instead turn it like a top so that a tip is directly up, and a tip is directly down. Now saw it above the center line at at point that will give you the desired table percentage size. You will end up with a square preform but with the Crown angles, and pavilion angles already in. Now all you have to do is round out the shape, and lay the facets on. You will end up with two stones, saving about 50% of the original cube weight.

The picture of the process below is for a Diamond sawable, which is actually a most often a dodecahedral, but also commonly a cube. In a colored stone you can just accept the 45 degree angles of the rough rather than the exact angles that diamonds require.


I think you will still end up with a stone of the same diameter as if you put your dop on one of the original flat surfaces. So any way you slice it, a 10 mm cube at most give you a 10 mm round stone. Even with 45 degrees on the pavilion, the yield is still only 22%, and the stone certainly wouldn't perform to the standards of something I would sell. If you could get something for a second stone it would be much smaller, so both together wouldn't come close to 50%, and you would need to account for the material lost by the saw kerf.

Image
Image

_________________
Precison Gem
www.precisiongem.com


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Sun Aug 14, 2022 7:06 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
Here is a good discussion of how yield works with lab grown diamonds which have consistent shapes close to a cube. The expected yield is about 50% whether you are getting one 40% yield and one 10% yield stone, or two 25% yield stones.

As I said, these are actually dodecahedrons, which are very close to cubes. I am basing my yield on actual results of parcels of sawable diamond roughs I have bought and processed over the years. If there is an error on my part it will be because of differences between dodecahedrons and cubes. But I feel instinctively that in any case my final yield will be closer to 50% than it is to 20%. In most instances because of how Diamond values work we would chose a larger 40% yield larger stone, and sacrifice the size of the second stone a bit for a smaller total yield. This is the standard in the Diamond cutting industry.


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Sun Aug 14, 2022 7:35 pm 
Offline
Platinum Member
User avatar

Joined: Wed Mar 15, 2006 5:10 pm
Posts: 2117
Location: Maryland
1bwana1 wrote:
Here is a good discussion of how yield works with lab grown diamonds which have consistent shapes close to a cube. The expected yield is about 50% whether you are getting one 40% yield and one 10% yield stone, or two 25% yield stones.

As I said, these are actually dodecahedrons, which are very close to cubes. I am basing my yield on actual results of parcels of sawable diamond roughs I have bought and processed over the years. If there is an error on my part it will be because of differences between dodecahedrons and cubes. But I feel instinctively that in any case my final yield will be closer to 50% than it is to 20%. In most instances because of how Diamond values work we would chose a larger 40% yield larger stone, and sacrifice the size of the second stone a bit for a smaller total yield. This is the standard in the Diamond cutting industry.


Well this came up due to the article by Glenn Kline where he talked about 20 to 25% recovery. I think his article was geared for hobby cutters who enjoy cutting, mostly cut lab created material or very inexpensive natural material. Some of these guys submit stones for competition, where perfection is the name of the game. I'm sure your typical stone wouldn't score very well in these types of things.

My point was, if you are cutting inexpensive lab material, or very inexpensive natural rough, then this makes sense. If you cut a 10 mm cube, then trimmed off one point, after the saw kerf, what would you be left with? Maybe 8 cents of material? Was that worth the time to saw it? What's the chance you will get a perfect saw cut an not by mistake make the larger piece smaller than needed! If you are cutting a diamond, sure it's worth it, but not lab material or a cheap blue topaz or citrine.

I still think I should send you a perfect cube for you to produce the 50% recovery on. And keep track of your total time cutting and sawing. In your initial posting I think you were talking about 1 stone, not 2. You said:

"You give me cube shaped (which is a square in all directions) and I should be able to get very close to a 50% recovery in a SRB cut round. More if you don't need a standard brilliant cut."

_________________
Precison Gem
www.precisiongem.com


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Sun Aug 14, 2022 9:41 pm 
Offline
Gold Member
User avatar

Joined: Tue Apr 05, 2016 7:58 pm
Posts: 1424
Location: San Marcos, CA
I know this is a GCS cube test to prove some point of waste experiment. But as stated earlier this weekend somewhere, unless there is a proverbial saw blade rigid or pliable in GCS. GCS studio was not designed to save off trim cuts and utilizing the depth of cut feature is an arbitrary grinder of sorts.
Attached is a pdf of what ever you want to make of it cutting a SRB starting with the exact needs of material 66.5% not a square cube.

This image depicts preforming the cube via trimming, not grinding a square into a round.

Attachment:
vt-0001.jpg
vt-0001.jpg [ 92.21 KiB | Viewed 1069 times ]


Set some parameters for a valid test and the discussion.
A 4mm Montana sapphire is what it is and of course no one is going to trim cut it to save any thing, a 40 carat Montana sapphire that is a story of its own.
Preforming is not just sitting down and grinding away.

Yes we were basically addressing hobby cutting then it went to saving minutes and cents.
How is there now a cost and time analysis attached in the Glen Klein concepts generally addressing hobby cutters who just enjoy cutting?


Attachments:
Vol_Test-SRB.pdf [102.29 KiB]
Downloaded 33 times

_________________
The Gem Garden
San Marcos, CA
Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Sun Aug 14, 2022 10:50 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
The problem is as Greg says GCS is not designed to properly simulate the cutting with this orientation of sawing.

Also what some are missing is that once you rotate the cube orientation, the Length and width both remain 10mm. But the usable depth of the rough is now equal to the Hypotenuse of a 10 X 10 Right Triangle which is 14.142 mm. Obviously we now have way too much depth to efficiently cut a single stone for maximum yield.

So, if we saw the rough into two equal pieces (this makes the test easier, but we could use different proportions), Let's allow .25 mm for the width of a saw blade, we end up with two rough stones with dimensions of 10 X 10 X 6.95. 69.5% depth is really too deep to cut a SRB at Gene's ideal angles without too much loss. I might likely cut two classic Portuguese style rounds with such a piece, but there are a number of other cuts that would work well with these proportions.

Working with quartz the original 10X10X10 cube will weigh about 13.25 cts according to GCS. If I cut two of the Portuguese cut stones describe above, GCS says that each will weigh 3.51 cts. This is a total weight of 7.02 cts. for a total yield of 53%. Easily making the goal of a 50% recovery.

Yes parameters of cuts, and angle and someone's personal standards could be applied to the experiment to that would limit yield and result in less than 50%. But the stones as envisioned would be very attractive, cut with precision, with excellent meet points, polish, and stay above the critical angle of quartz.

As we can all see, there are many ways to approach such a challenge and I won't judge them. I will acknowledge that Gene and I would likely make very different choices with such things. That is OK.

Here is a diagram done in GCS that is within the discussed measurement parameters. It is a classic Portuguese Round that show the results. You can download the GCS PDF Cutting Diagram as well.

I think the difference I didn't account for originally was that with a dodecahedron with sides of 10mm you end up with the Hypotenuse for a diameter. Then you should be able to make a single stone very near 50%.


Attachments:
10X10Challenge.pdf [65.68 KiB]
Downloaded 30 times
10X10Challenge.jpg
10X10Challenge.jpg [ 103.77 KiB | Viewed 1066 times ]
Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Sun Aug 14, 2022 11:17 pm 
Offline
Platinum Member
User avatar

Joined: Wed Mar 15, 2006 5:10 pm
Posts: 2117
Location: Maryland
1bwana1 wrote:
The problem is as Greg says GCS is not designed to properly simulate the cutting with this orientation of sawing.

Also what some are missing is that once you rotate the cube orientation, the Length and width both remain 10mm. But the usable depth of the rough is now equal to the Hypotenuse of a 10 X 10 Right Triangle which is 14.142 mm. Obviously we now have way too much depth to efficiently cut a single stone for maximum yield.

So, if we saw the rough into two equal pieces (this makes the test easier, but we could use different proportions), Let's allow .25 mm for the width of a saw blade, we end up with two rough stones with dimensions of 10 X 10 X 6.95. 69.5% depth is really too deep to cut a SRB at Gene's ideal angles without too much loss. I might likely cut two classic Portuguese style rounds with such a piece, but there are a number of other cuts that would work well with these proportions.

Working with quartz the original 10X10X10 cube will weigh about 13.25 cts according to GCS. If I cut two of the Portuguese cut stones describe above, GCS says that each will weigh 3.51 cts. This is a total weight of 7.02 cts. for a total yield of 53%. Easily making the goal of a 50% recovery.

Yes parameters of cuts, and angle and someone's personal standards could be applied to the experiment to that would limit yield and result in less than 50%. But the stones as envisioned would be very attractive, cut with precision, with excellent meet points, polish, and stay above the critical angle of quartz.

As we can all see, there are many ways to approach such a challenge and I won't judge them. I will acknowledge that Gene and I would likely make very different choices with such things. That is OK.

Here is a diagram done in GCS that is within the discussed measurement parameters. It is a classic Portuguese Round that show the results. You can download the GCS PDF Cutting Diagram as well.

I think the difference I didn't account for originally was that with a dodecahedron with sides of 10mm you end up with the Hypotenuse for a diameter. Then you should be able to make a single stone very near 50%.


Sawing the cube the way you describe, you will not be able to cut 2 stones with a 10 mm diameter.

_________________
Precison Gem
www.precisiongem.com


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 12:09 am 
Offline
Gold Member
User avatar

Joined: Tue Apr 05, 2016 7:58 pm
Posts: 1424
Location: San Marcos, CA
Counting cat hairs now are we. Challenge was about getting a 50% yield not a 10mm exact diameter. :roll:
The truth is 10mm is an arbitrary number for easy calculations is all I am gathering from the stated dimensions.
So if you get two 9.5mm rb's will their combined weights come to or close to the 50%?

_________________
The Gem Garden
San Marcos, CA


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 12:01 pm 
Offline
Platinum Member
User avatar

Joined: Wed Mar 15, 2006 5:10 pm
Posts: 2117
Location: Maryland
I think if you had a solid modeling program, you would see that if you cut a cube as described, you can not even create a 9 mm circle on the surface at it's largest place. Now if you take into account the material lost from the saw blade, and then placed the table on that surface you need to project down the height of the crown before you get to the location for the girdle. The girdle is the diameter. With this approach you will get a max diameter around 8 mm or less.

Using his port cut, then the weight would be 2.65 ct per stone.

This all assumes you get a perfect saw cut exactly where you want it. I think that would be a difficult cut for me to make, holding the cube on one point, and starting the saw cut exactly on another point.

If everything is perfect, you could maybe get 2 stones with 40% recovery.

I think the only way you guys will understand this, is if I send you a 10 mm cube, you cut it and see what you get.

For me, if I was to cut a round from the rough, dop it on one of the faces and start cutting the stone. No preforming, no additional sawing. Done in 1 hour.

_________________
Precison Gem
www.precisiongem.com


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 12:42 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
As I said cutting exactly in the middle is not optimum. You would cut at the table diameter height above the middle. In this way you would get one major stone, and one minor stone. The major stone would yield a 10mm diameter or minus only a couple of 10ths of a millimeter for girdle width.

I will concede that in most cases we would end up with just under 50% total yield in a production environment. But that is still double the yield of the low 20% yield that was originally claimed.

As for the time taken to cut, yes cutting a SRB without regard to yield is a very fast way to cut. It should be able to be accomplished somewhere near an hours time. However, the value of time over material only applies to very low value rough. The higher the value of the rough the more value other approaches achieve.

Anyway I am growing tired of this discussion. My original point was that one shouldn't accept that yields in the 20%-25% are inevitable. In most gem cutting shops I know of that cut valuable material yields in in the 35% range are expected, and yields much higher are commonly achieved.

Take a look at Richard Hughes Ruby and Sapphire Book. He shows a number of stones as the proceed through the rough - preform - finished stages. He show pictures of all stages that show that these are fairly normal shaped rough.

Sample Ruby

1: 15.79 - 9.3 - 8.52 yield 54%

2: 19.77 - 9.21 - 8.41 yield 43%

3: 22.3 - 14.29 - 13.22 yield 59%

Average yield for this parcel 52%


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 1:10 pm 
Offline
Platinum Member
User avatar

Joined: Wed Mar 15, 2006 5:10 pm
Posts: 2117
Location: Maryland
I'm getting tired of this too, but you keep stating things as facts that are just wrong. Then you keep changing your answers.

First you could get "A stone" of 50% or more.
Then it was 2 stones, one smaller.
Then it was 2 identical stones of 10 mm.
Now it's again one 10 mm stone and one smaller stone.

The FACT is if you slice a cube they way you describe the resulting flat surface is a triangle. It's impossible to pass a cylinder through the piece of even 9 mm and still have a plane where you could make a level girdle. I know, I made this model in SolidWorks years ago. I no longer work with my previous employer, so I don't have a work Windows computer with SolidWorks on it, but I may have a very old version on an old PC that I haven't turned on in 10 years. If so I'll make the model again and prove it to you.

From a cube, the way to cut the largest stone if dop on one of the flat surfaces.

If you insist you are correct, let me mail you a cube and prove your case.

I know you don't like meet point cutting, yet there are many professionals in the USA and other places cutting this way and selling stones. To call these people hobby cutters is not true. A hobby is something people do for enjoyment, a professional is someone how makes money doing it as a profession.

_________________
Precison Gem
www.precisiongem.com


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 1:16 pm 
Offline
Platinum Member
User avatar

Joined: Wed Mar 15, 2006 5:10 pm
Posts: 2117
Location: Maryland
My yield over several thousand stones excluding lab created is an average of 37.4%

For the lab created it's 24.5%. Lower because of the straight edges from saw cutting and because I will usually saw a piece a little over size just to make sure I don't have any issues getting the requested size. Most all my lab stones are per request, so I am not taking a piece of rough and trying to optimize it, but rather meet the customers request.

_________________
Precison Gem
www.precisiongem.com


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 2:00 pm 
Offline
Gold Member
User avatar

Joined: Tue Apr 05, 2016 7:58 pm
Posts: 1424
Location: San Marcos, CA
No Gene, that is not the only way I am going to understand this. Your challenge, test what ever you want to call it is a bunch of crap and you know it. You like to twist most everything around to fit within your greatness of un-founded self proclaimed success.
The point is if you get a cad program (solid modeling) you will understand this one fact coming that shoots down the SRB cube test.
It is somewhat offensive that you somehow want to project down the center that I do not know the difference without doing a challenge that fails from the start.
Hobby cutter, Commercial Cutter, and or the ultimate professional cutter only needs to know how much material they need for a given cut. The fact.
You do not need a square cube to cut a round stone of any variety of design and if you start with a square cube you end up in the hobby Cutter category as it pertains to this discussion not as your derogatory projection.
Take a look at the pdf I uploaded earlier, to cut that stone I need only 66.5% of a 100% cube. In my understanding GCS does not give that back if you cut any stone starting with a hobby cutter square block.
I can saw out any LxWxD from stock and get the maximum yield from each and every piece, when yield is the goal.
One question needs answered at the start of every cutting project how much depth do you have at given orientation to get a maximized yield.

_________________
The Gem Garden
San Marcos, CA


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 2:50 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
I am not on an ego driven quest to prove someone wrong and myself right. Others see through this game. I am only trying to share my opinions with other members of this community in order for all of us to learn.

I am backing out of this conversation before it becomes personal.

Thanks all.


Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 3:15 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
Precision Gem wrote:
The FACT is if you slice a cube they way you describe the resulting flat surface is a triangle. It's impossible to pass a cylinder through the piece of even 9 mm and still have a plane where you could make a level girdle.


Absolutely not true. Maybe that is why you are seeing things so differently about the diameters and depths that can be achieved.

Below is a cross section of the cube after the slice. You will notice that it is a perfect preform of a cut stone. Facets can be laid on with very little loss.

I have also included a top down view to show both the table and diameter. Clearly it is a rectangle, not a triangle. The length is equal to the hypotenuse of a 10 X 10 Triangle or 14.142mm. More than enough to achieve a 10mm diameter circle and leave room for crown and girdle. The width is 10mm. But in this direction the sides are at 90 degrees so the entire width can be preserved when making the circular outline and the crown.


In Gem Cut Studio set the the Index to 12 to move the cut to a corner. Set the symmetry to 1 to cut a single plane (the table), and the angle to 90 degrees to orientate the cut. You will see you get exactly a preform as pictured below. Not a triangle for sure. I encourage anyone to try it for themselves.


Attachments:
SlicedCubeTopView.png
SlicedCubeTopView.png [ 22.71 KiB | Viewed 1014 times ]
SlicedCubeCrossSection.jpg
SlicedCubeCrossSection.jpg [ 57.46 KiB | Viewed 1014 times ]
Top
 Profile  
Reply with quote  
 Post subject: Re: What causes a misaligned pavilion girdle before transfer
PostPosted: Mon Aug 15, 2022 3:31 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
As an aside I also encourage everyone to look once again at the Sample cutting parcel Richard Hughes used in his book.

Sample Ruby

1: 15.79 - 9.3 - 8.52 yield 54%

2: 19.77 - 9.21 - 8.41 yield 43%

3: 22.3 - 14.29 - 13.22 yield 59%

Average yield for this parcel 52%

Notice that almost all of the weight loss takes place in the preforming process. During preforming the stone is not restricted in any way by limitations of the machine or how the stone was doped. The retention of material achieved when laying on the facets is extremely high often close to 90% retention. Also realize that during the laying on of facets whether the stone is centered on the dop or not is irrelevant.

The book contains a number of such examples. This one is the opening page of the Methods of Fashioning on page 318. If you look at the finished stones they are very nicely finished with very good meet points polish a symmetry. The market would give no deduction for cutting, nor any premium for better cutting. These stones will sell for tens or hundreds of thousands of dollars. Other samples in the book have sold for millions of dollars with similar cuts. This is how almost all gems in this value range are cut.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 64 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 31 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock