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#1

Greybeard
Member
From: Toowoomba, QLD
Joined: 21 September 2016
Posts: 24
Member
26 October 2016 09:55 am

Looking for 64 index designs I am finding a lot of designs with fractional angles. For example, a standard brilliant with angles like 42.3 or 19.8 for the crown.

On my old manual machine which has simple manual marked angles it would be impossible to set the angle to fractional amounts. Accurately getting whole numbers is a challenge and maybe I can get half degrees but .8 or .3. No way.

If I round these to 42 and 20 will this make a lot of difference with the brilliance?

#2

AtomRat
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From: Katazone, VIC
Joined: 22 May 2014
Posts: 5,002
Member
26 October 2016 11:42 am

Does your main index arm have a 'cheater' knob? You use the cheater to set thise finer angles. The exact angles help the light exit the stones correctly but imo, not essential while learning to just use the machine.


Wisdom is knowing how little you know

#3

Lefty
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Joined: 01 May 2014
Posts: 936
Member
26 October 2016 01:46 pm

I have rounded fractions that were close to whole numbers with no detriment whatsoever to the stone.

I have altered angles by a couple of degrees with no noticeable impact - though I would be careful lowering pavilion angles in case you fall foul of the critical angle - the angle at which light entering the stone through the top will not be reflected back as brilliance but will simply pass out through the bottom. Critical angles vary with different materials - quartz is about 40.5 degrees, feldspar (labradorite) about 41.5 (I think). Sapphire is much lower at about 34.5 (again, if memory serves correct) - the lower the materials critical angle, the more leeway you have to shallow the stone....to a point. Get too close and you'll get "tilt windowing" - I once cut a piece of smoky quartz in a design with angles meant for materials of a higher refractive index, the result was a flash of brilliance in one half of the stone and in the other half I could look right through it and see my fingers and the gem grabbers underneath.

Even with sapphire some say never take the culet angle below 39 degrees - I've never gotten quite that close but 40 degrees still produced a nice, brilliant stone.

The crown angles are somewhat more forgiving than the pavilion angles since it is the pavilion that is the primary reflector.

As long as you remember what you rounded them to - write them down - and steer clear of the critical angle when cutting the pavilion, small rounding changes to angles should make little or no difference.

1 user likes this post: fossickeract

#4

Greybeard
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From: Toowoomba, QLD
Joined: 21 September 2016
Posts: 24
Member
26 October 2016 10:09 pm

AtomRat wrote:

Does your main index arm have a 'cheater' knob? You use the cheater to set thise finer angles. The exact angles help the light exit the stones correctly but imo, not essential while learning to just use the machine.

Thanks AtomRat, but this isn't the index but the facet angle to the girdle, if I am explaining it right. My old machine has a 90 degree protractor so no fine adjustment.

#5

Greybeard
Member
From: Toowoomba, QLD
Joined: 21 September 2016
Posts: 24
Member
26 October 2016 10:11 pm

Thanks Lefty. Great advice. I will keep all this in mind.

#6

B5MECH
Member
From: Sydney, NSW
Joined: 25 January 2016
Posts: 2,190
Member
26 October 2016 10:36 pm

I maybe p@#$ing in the wind but is there some sort of digital angle gauge you could fit to an older machine so you would set it to straight, zero the meter and use the digital readout for the correct angle
I've never looked into a digital angle meter but you can fit similar to a old lathe for a digital measurement readout
I'm more into lathes milling and grinding machines for metal but have always been interested in stone cutting
Interesting topic GB
1477482742_210170_inset4_xl.jpg
Like the gauge on that mounted to the pivot point

Last edited by B5MECH (26 October 2016 10:53 pm)


Garrett At Gold, Garrett gravity trap gold pan kit, Makro Racer 2, Makro Pointer.

#7

Kingsolomon
Member
Joined: 16 May 2013
Posts: 489
Member
30 October 2016 01:27 am

Cut your pavillion at 41mains and 42 1/2 breaks in anything and you'll be alright smile


Got stuff to dig stuff up .. Got stuff to detect metal stuff .. Got stuff to facet stuff ...

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