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Author Topic: Fitting a facet design to a piece of rough  (Read 781 times)

RoughCreations

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Fitting a facet design to a piece of rough
« on: April 09, 2024, 01:11:26 PM »
I have been doing a proof of concept for fitting a chosen faceting design to a piece of gem rough using 3D software and an automatic algorithm. Yes, I probably have too much time on my hands, but I do a lot of 3D modelling in my paid work, so it doesn't hurt to have a play. The aim is to get the best yield possible from a design-rough geometry perspective.

The fairly random facet design I used for testing purposes is "Watch" by Dan Starr



The gem rough is a chunk of smoky quartz. I painted it in ochre to reduce reflections which allows a better 3D model to be created by the software.



34 images of the rough were taken at different angles. A patterned "Zebra" base was used which allowed the 3D processing software to better understand the orientation.
The set of images were first processed into a point cloud, and then a mesh object.





The gem design and the rough were imported into 3D software and then enmeshed together.



The challenge is to see if doing the best-fit step can be automated. This is the key point in the whole process, it can be done manually with the software as I have done in the picture above, but full automation is the aim.

RC
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Manficat

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Re: Fitting a facet design to a piece of rough
« Reply #1 on: April 09, 2024, 11:05:11 PM »
This is way beyond me  ;) this would probably be quite helpful for faceting. what kind of things do you 3d model in your paid work?

RoughCreations

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Re: Fitting a facet design to a piece of rough
« Reply #2 on: April 10, 2024, 10:32:11 AM »
It may be useful for the computer-keen person with a piece of high value rough.
I 3D-model mineral deposits in my paid work as a geologist and then calculate a resource (tonnage and grade).
Incidentally, if anyone reading this (or someone they know) needs a mineral resource calculated, let me know - special price for Forum members, lol.

RC
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bush

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Re: Fitting a facet design to a piece of rough
« Reply #3 on: April 10, 2024, 05:12:48 PM »
What cad are you using?
I'll see if I can create a script or plugin to calculate the best fit

RoughCreations

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Re: Fitting a facet design to a piece of rough
« Reply #4 on: April 10, 2024, 06:17:37 PM »
What cad are you using?
I'll see if I can create a script or plugin to calculate the best fit
Meshroom for the photogrammetry, and Blender for the best fit. I might also try MeshLab for the best fit as it is easier to use. They're all free and open-source software.
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Alaskan

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Re: Fitting a facet design to a piece of rough
« Reply #5 on: May 17, 2024, 05:54:10 AM »
I was asking andrewbrown about the small stones we see selling from around the world and not having any clue as to how to choose a design...

... or the expectation of having a finished product of what... 50% of the size of the rough being optimistic?

What kind of product to expect from a 2.5 carat sapphire or garnet... will wait for your experience... thaks.

RoughCreations

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Re: Fitting a facet design to a piece of rough
« Reply #6 on: May 17, 2024, 01:07:07 PM »
I was asking andrewbrown about the small stones we see selling from around the world and not having any clue as to how to choose a design...

... or the expectation of having a finished product of what... 50% of the size of the rough being optimistic?


50% yield from a specific piece of rough is generally very optimistic, generally only achievable if your rough has a freakily-good shape or has been pre-formed by the seller (rare) and would therefore command an extra premium in the asking price.
I think a 25 - 33% yield calculated over many cut stones seems to be closer to the average that normal facetors achieve. Carefully choosing a design to match the shape of your rough would get you closer to 33% average, with nice prismatic rough such as tourmaline crystals etc definitely helping in this regard. Highly irregularly-shaped rough with shallow projections usually means closer to the 25% yield, with unexpected inclusions discovered and requiring removal during the cutting process also affecting the final yield. Other factors such as human error while cutting can also combine to reduce the yield for a given stone, and affect your average too.
Quote
What kind of product to expect from a 2.5 carat sapphire or garnet... will wait for your experience... thaks.
So, bearing in mind all that, the answer to your question is unfortunately: That depends....
If I was buying a 2.5ct piece of sapphire rough, I would be focussing on nice clean regularly-shaped offerings only, with the aim (hope?) of getting an 0.8ct finished stone.

RC
« Last Edit: May 17, 2024, 01:09:14 PM by RoughCreations »
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Alaskan

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Re: Fitting a facet design to a piece of rough
« Reply #7 on: May 17, 2024, 09:30:51 PM »
Thank you RC for your kind reply to a novice - exactly answered my question. I live on an island in the southeast passage of Alaska.  It's mail or internet. To know my experience of carving small stones out of generous chunks is expected... encouraging. Your explanation was superb. This is a post I'll print and pin to the wall in my humble shop.

Have you any insight on 'microscopic' tiny disintegration on a facet at 14 K Corian after no preforming coarser than 400? Material is Pnom Penh lab created Zircon cut with a .014" saw and stepped up with 600 1500 steel then 3000 8000 to 14K on Corian.

Is this material 'weak' or is it sub-surface 'damage' from a squarish block cut with the saw which seems the harshest treatment this material endured. I'm 80, retired, and getting stupid - don't want to be a pest.


Alaskan

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Re: Fitting a facet design to a piece of rough
« Reply #8 on: May 17, 2024, 09:48:02 PM »
Preformed with 400 steel... did I mention I was getting stupid? 🥴

MakkyBrown

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Re: Fitting a facet design to a piece of rough
« Reply #9 on: May 18, 2024, 02:14:07 AM »
Good to see you made it to the forum Alaskan.

RC Alaskan has a Patriot 8 faceting machine.  :)  Looks a very nice machine, a lot to like about the faceting head. 
https://www.sierragems.net/proddetail.asp?prod=PAT_08
Alaskan does your machine have the digital readout?
Cheers
MB


Alaskan

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Re: Fitting a facet design to a piece of rough
« Reply #10 on: May 18, 2024, 02:18:51 AM »
Yes the Patriot 8 has a digital readout to a tenth and I use the dial indicator to get closer to Andrew Brown's design digital hundredths... ~12 dial indicator tenths are tripping both ends of the digital tenths readout.

You are AB got it! 🤦‍♂️
« Last Edit: May 18, 2024, 02:36:13 AM by Alaskan »

MakkyBrown

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Re: Fitting a facet design to a piece of rough
« Reply #11 on: May 18, 2024, 10:56:55 AM »
Yes the Patriot 8 has a digital readout to a tenth and I use the dial indicator to get closer to Andrew Brown's design digital hundredths... ~12 dial indicator tenths are tripping both ends of the digital tenths readout.

You are AB got it! 🤦‍♂️
The optical encoder on your machine could easily be swapped out for a 5000cpr one giving 0.018degree angles steps.(you may only need a new code wheel and reader). BUT you would also need to make a new screen/control box to display the angles. I would only recommend doing this if you had an electronics background. Inspired by Tom Herbst book a few of us on here have fitted encoders to our machines and refined Tom's design/code at bit. The hardest part for me was figuring out how to mount the encoder and your machine already has one mounted on it. It can also be hard to learn to program in the Arduino environment and make changes to the existing code to suit your machine/new screen.

MB

Alaskan

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Re: Fitting a facet design to a piece of rough
« Reply #12 on: May 18, 2024, 11:10:32 AM »
Thanks MB it's summer here and warm enough to be faceting in my shed/workshop - next Fall when the 100 mph winds and freezing cold arrives I'll look deeper into it - I have Tom Herbst books and found them challenging - a lifetime of knowledge isn't easy to consume.

I'm dog-paddling - learning by doing.

 

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