Hi,

I have been searching for technical drawings / cad files depicting the exact
way a so called "Sugarloaf"-Cabochon cut is carried out to build a model in MOI.

As I where unsuccesful I hope to find some one here to point me in the right
direction so tips are very welcome !

TOM

For the gem itself take a box then from views sides make some Boolean Diff by a simple curve!

Hi dear Pilou,
Thank you ! The surface is rounded so a simple Boole would not be enough.
The shape looks simple at first glance but is quite sophisticated when one
takes a closer look. Maybe I should look for a specialized forum to ask
for more details ,,,

Hi Tom,

After a lot of searching, I was unable to find a CAD file of a sugarloaf cabochon cut.

The definition is here:
https://emeralds.com/education/all-about-emerald-cabochons/

The cabochon cut is not really a facet cut. It has rounded sides.
The cabochon cut is a very old cut/grind.
The sugarloaf is a "square" rounded pyrimidal cut/grind.
Some lapidarist cut a square facet design, and then grind off to rounded sides.
The work is done by hand, so there are many possible designs.
Your picture shows grooves cut, for the mounting. This is not always done, if another mounting can work.
The bottom can be round or flat, below the "girdle".

It seems easy enough to boolean together some dome shapes in MoI, to make the rounded sides. Plus some fillets.

- Brian

https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=8&t=16088
https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=37&t=21928&hilit=sugarloaf
https://www.gemologyonline.com/Forum/phpBB2/search.php?keywords=sugarloaf&terms=all&author=&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search
https://forum.rocktumblinghobby.com/thread/85775/new-faceting-cad-program?page=1

Try a revolve...






Unhide curves to see the curves, make the vertical one pointier if you want more of a point.
Then use a rail revolve, the vertical curve being the profile, the ground one being the rail, use a straight z axis as revolve axis.

Hope that helps...

Here is a way to get close...



then, if you want those 4 edges to be harder, you can create some lines and trim some edge loops near, like in poly modeling and it will harden the edges you want. Takes just a bit more work to be sure you keep supported polygon types...

Here might be a bit easier using the "Loft to a Point" option.

Oh wow you are awesome, thank you so much to you all
for those amazing guides - fantastic !!

another proposition... an intersection of spheres

4 spheres made with circular array.

You boolean intersect them.
Next you cut to have only the mid top.

Next you chamfer the bottom.

I have made a second version with opposite spheres scaled with 0.1 mm less if you want the edged top.

Adapt the height as you want...


To have surfaces for the claws, rotate your stone and cut with a curve.

All steps inside the 3dm file

Here are some multiviews, video, and dimensions:
https://www.rafjewels.com/search?q=emerald%20sugarloaf%20diamond

- Brian

Looking at google pics it seems like they very a little bit if they come to a point or not so that is going to be hard to find a cad profile for the requirements. I did find a reference here though with a description, I used a point in this example.

https://emeralds.com/education/all-about-emerald-cabochons/

Bemfarmer already showed the source..

Pilou, bemfamer, Death, Burrman, Phiro, Grendel, you are awesome and your input
is very much appreciated.

This Cabochon shape is really interesting, it looks like four symmetrical planes with
a curved tip and the very top unifying all four surfaces being additionally rounded in
a bit different way.

In regard of this endeavour I stumbled over the great little Squircle Script - is there a
difference in it to the "perfect ellipse" script which I was unable to find ?

TOM

I think that the "super-ellipse" has more generalized, elaborate mathematics, than the squircle script.
(The squircle is a subset of the super-ellipse...)
(I like Burr's method, for the Cab.)

The squircle shape for the outline of the gem is nice.
The lower portions of the Cab gem seem to vary, and are important for mounting...
Read that the bottom is often not polished, for light reasons, and can be flat or rounded.
It is difficult to cut, for perfect symmetry. Have not seen the special tool machine which could be used...

- Brian

The Squircle (still strugelling with this word ;-)) script is really useful.

Taking a closer look at available photo material it seems
that the 4 edges start almost completely rounded at
the bottom sharpening towards the tip. The tip itself
being a surface of its own filling the gap between
the four surfaces.

Hi Tom,
perhaps this method will give you the rounded peak needed.
I started with a square and added mid points to each side.
Then selected the mid points and scaled to give the desired curvature,
Offset copies made and added point for peak then lofted as per Burr's video.
Added a fillet running diagonal from corner to corner.
The other diagonal same radii but requires a second fillet set for the peak area to be slightly smaller.
hope that makes sense.
Cheers
Barry

Here is another option...

Since it seems the surgarloaf is more of an "artistic grind" and not really a mathematically produced result, you can change the base shape and all the angles of the surface structure, along with Blend parameters to "Eyeball" some various results... All smooth.

Sugarloaf cut video. Not in English (India).
https://www.youtube.com/watch?v=dsfqdqgxEyE

- Brian

Google search of "Cabo Gem Cut" shows several videos, (but not for sugarloaf), and the grinding equipment.

Amazing approach, Burrman. The video shows you using the Superellipse script.
Is there any difference to the Squircle script ?

It is Burr's video that you refer to?

- Brian

Uh I guess I mixed up your names ... Yes, the Video shows Burrman using
the Superellipse script and as I did not find this one (I am using the "Squircle")
I wondered about the differnces.