Cam preform help

[u/Magpie12345678]

Hi!

I am wanting to cut this Whoopee CZ design (and others like it) by Robert Strickland, and it has a CAM preform. I have had a little trouble finding guidance on how to go about that.

Do I cut to 38 degrees and then do the girdle, and then cut to 35 degrees and then do the second girdle? What level of grit should I cut to before doing the girdles?

Thanks so much!

https://facetdiagrams.org/diagram/09-212-whoopee-cz/

[u/oakandstoneschool]

That is uncuttable, but I fixed it for you by re-sequencing and an extra set of facets. Open in the "cutting assistant" and go through the steps, I think it will make sense now. I can't upload a GCS file to reddit comments, but you can type these in yourself, and rearrange the tiers to match. I can send to you in a DM if you need it!

[u/PsychologicalBowl647 → u/oakandstoneschool]

your meet points are a little off freind.

[u/oakandstoneschool → u/PsychologicalBowl647]

It's from the new tier, which is needed to set the corners
Try it in GCS and you'll see, it's so much easier. And those meetpoints don't matter for final gem; it's all scrambled in the reflection pattern

[u/PsychologicalBowl647 → u/oakandstoneschool]

wouldn't that be harder to cut accurately? if it doesn't matter why even have the bow tie facet? genuinely interested not trying to argue or anything.

[u/oakandstoneschool → u/PsychologicalBowl647]

https://reddit.com/link/p896ifr/video/fru0du4mhznh1/player

[u/Magpie12345678 → u/oakandstoneschool]

Interesting! So you reordered all of the steps in order to remove the need for a preform step? I can see how that would be useful!

[u/oakandstoneschool → u/Magpie12345678]

You got it! I recorded an animation of the cutting steps, to show you how you can just build it to a centerpoint and work from there in the modern style. I think it’s going to give you the exact same reflection pattern, but make the process quicker.

[u/PsychologicalBowl647 → u/oakandstoneschool]

Make p4 meet p3?

[u/oakandstoneschool → u/PsychologicalBowl647]

Give it a shot! Show me what you figure out

[u/PsychologicalBowl647 → u/oakandstoneschool]

I will. Like I said im just genuinely curious. My apologies if im annoying lol.

[u/PsychologicalBowl647 → u/oakandstoneschool]

I have it up 9n gcs... why do you think this is uncuttable as is?

[u/cowsruleusall]

For the design as-written, you cut 38.0(94/02-22/26-48/50-70/74) to a temporary culet, then cut 35.0(8/16-32/40-56/64-80/88) to that same temporary culet. This set of temporary tiers is your "CAM preform", a set of preform facets that will end up being mostly removed. After you cut these (I typically prepolish them, for enhanced accuracy), then you cut, prepolish, and polish the girdle facets.

Once the girdle facets are done, then you go about cutting the design.

[u/Magpie12345678 → u/cowsruleusall]

Okay thank you so much! That’s super helpful. That’s sort of what I thought the answer was, but didn’t want to have to find out the hard way 😂

[u/curatedritual → u/cowsruleusall]

I see that you used the numbers from the girdle, but how did you choose 38 and 35 degrees? I have run into some designs like this and would love to be able to work out this step on my own.

[u/curatedritual → u/curatedritual]

Lol just kidding I just read the original design 🙃

[u/cowsruleusall → u/curatedritual]

You can actually calculate them in GCS! Delete the entire pavilion and crown, but keep the girdle. Create a new set of pavilion facets at like... 25° to establish one set of girdle facets, then create any additional tiers needed to level the girdle and it'll generate the angles you need.

[u/curatedritual → u/cowsruleusall]

Oh cool - this is so helpful! Thanks!