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 Post subject: Facet question on setting precise index.
PostPosted: Mon Mar 25, 2019 2:33 pm 
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Hi all,

Hoping you can help.

Just a quick question from a newbie really. I will get straight to the point.

If I am to follow a faceting chart but cannot precisely set an angle such as 19.8degrees how much of a problem could this be if I say go ahead and round up to 20degree in this example.

The reason I ask is my facet machine doesnt have a digital angle read out and is mechanical, therfore I set the angle mechanically and never know to two deciamal places as in some of the digital machines out there.

I am using a sterling lapidary machine for any one that may be curious.

Thanks in anticipation


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 Post subject: Re: Facet quastion on setting precise index.
PostPosted: Tue Mar 26, 2019 12:06 pm 
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(Apparently you are actually asking about cutting angle, not index.)

Don't worry about the second decimal place, just round off. You should try to estimate the tenths as best you can, but remember - "Cut a little, look a lot". Watch as your meetpoints come together and make small adjustments as needed. This is true even if you have a hundredths readout.

To make it easier, you might find a way to attach one of the relatively inexpensive (20-40 USD) digital angle gauges.


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 Post subject: Re: Facet quastion on setting precise index.
PostPosted: Tue Mar 26, 2019 12:35 pm 
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As Al said, don't worry about it. No matter the resolution of your angle gauge you will end up "walking" the meets in by eye. As you get close to the meet point cut a little, look often. You will develop a feel for it with practice.


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 Post subject: Re: Facet quastion on setting precise index.
PostPosted: Thu Mar 28, 2019 11:47 am 
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AlBalmer wrote:
(Apparently you are actually asking about cutting angle, not index.)

Don't worry about the second decimal place, just round off. You should try to estimate the tenths as best you can, but remember - "Cut a little, look a lot". Watch as your meetpoints come together and make small adjustments as needed. This is true even if you have a hundredths readout.

To make it easier, you might find a way to attach one of the relatively inexpensive (20-40 USD) digital angle gauges.



I totally agree on not worrying about the second place.

But he is talking about rounding from 19.8 to 20.


I looked at the stearling hand piece and it is only marked in degrees.

I am going to try and download a design into gemcut and try to show what it would do to the design to change the angle as described.


If you could I would look at getting an angle meter, that at least had the tenths of a degree

Do tyou have a particular design that you are starting with?


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 Post subject: Re: Facet question on setting precise index.
PostPosted: Thu Mar 28, 2019 12:34 pm 
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I choose a design "Road to Ruin" and modified the crown angles to the nearest whole degree.


here are the new cutting tables
Image
and a close up

Image

You will have to learn how to adjust the angles a little or you will have problems cutting some of the designs and getting them to look correct.

again a relatively inexpensive angle meter would help a lot.


I DO NOT want to discourage you.

but you may be able to try and at least get to the half of a degree that would let you get this close:

here is the cutting table with a .5 degree resolution

Image

and the crown (as I would probably cut it )

Image

I think it is a little better




you can estimage to at least a half of a degree, or for the original angle try a little more than half of the way between 37 and 38 to get closer.

or see if there is a way to make a vernier and add it so you can get the tenths of a degree.

I will see if I can find instructions on how to do that.


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 Post subject: Re: Facet question on setting precise index.
PostPosted: Thu Mar 28, 2019 1:06 pm 
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The Sterling machine is an excellent piece of equipment. I have worked with many cutting shops overseas where it is used in production. Rest assured that you will be able to produce high quality work with it.

Understand that although your protractor is only marked in certain increments, the number of settings in between the increments are pretty much unlimited, and your machine is capable of cutting at any of them.

Looking at the last image in Wilsons example we can see that what is needed is a slightly greater difference in angle between the bezel facets and the mains. This greater angle will spread the width of top of the facet to hit the proper meet points just as the main facet touches the meet point at the girdle. You can simply watch the facet growing, adjusting the angle as needed.

It is often easiest to leave facets a little under cut to leave a little room so that the meets are actually achieved during polishing. Especially if you are polishing with diamond as this allows you to move meet points easily. It is almost always easier to adjust an undercut facet that an over cut one.

In Wilsons second to last image example, the mains have already been overcut at a slightly too steep an angle. If you found yourself in this situation on an actual stone, you would have to fix it in one of two ways.

1.) Cut the table down to the meet points at the top of the non mail girdle facets. Then cut the girdle facets on either side of the main at a slightly steeper angle so they meet properly.


2.) Go back and fatten up the bezel facets to get room at the bottom to change the angle on the mains. This of course will require that your girdle is still thick enough to make this adjustment.

In Wilsons last image example the mains are still a little undercut at the top. To fix this is as easy as using a slightly greater difference in angle between the mains and girdles. Walk the mains in until the tops of the mains meet at the exact time that the main hits the girdle. An easy one step fix.

To accomplish this just raise the mast (in your case platform) very slightly, loosen the protractor until the stone once again makes contact with the lap retighten the protractor, cut and watch the facet grow. You don't really even care at this point what the number is.

learning to see these relationships will enable you to cut any pattern, accurately in a large range of L/W, H/W proportions, and maximizing the piece of rough. Get your head around the stone, what you are trying to accomplish with it, and away from the machine.


Last edited by 1bwana1 on Thu Mar 28, 2019 2:13 pm, edited 7 times in total.

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 Post subject: Re: Facet question on setting precise index.
PostPosted: Thu Mar 28, 2019 1:30 pm 
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If you have a jeweler friend (or someone else who is good with fine detail work)

You can add a vernier to your existing machine e that would get you to a .1 (tenth) of a degree.

Basically you scribe 11 lines evenly spaced over 10 degrees and you will get a vernier.

this is tbe best I could make quickly for you.

if you need to learn how to read them, there are plenty of online places.

Image


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