Tapered collet

For the purposes of this I am using a silly sized CZ to make it easier to see.

First measure the diameter of the stone Pic1, make a note of it, then measure the distance between the girdle and the bottom point of the stone and make a note of it, you will see from the pic2 I stuck the stone in some fimo and marked a line across the bottom to help get the girdle culet distance. My measurements in these pics are not exact as trying to hold the calliper and the camera at the same time is nigh on impossible.

Pic1

Pic2.

I am going to do the calculations on card to give you the idea, as I have no intention of setting this walloping big stone :0) when you do it use graph paper to make it easier to centre everything.

On your paper make a vertical line right down the middle. Pic3 Using this line mark the measurement of the diameter of the stone across the line so that the vertical line is the mid point Pic4 now using the measurement for the distance between the girdle and the bottom of the stone mark on the vertical line that distance then once again with the same measurement using the vertical line as the centre mark out the girdle culet distance horizontally Pic5 adding just a tad to allow for the rub over.

Pic 3 |

Pic 4 |

Now join up the ends and continue the line right down your paper till they meet, Pic6 marked in red. This point you have just made is the place at which you will be putting the point of your compasses.

Pic 6 |

So now take a pair of compasses and set them between these two points Pic7. And draw a circlePic8. Now adjust your compasses to get the distance from lower line to the pivot point Pic9 and draw a second circle. Pic9a

Pic 7 |

Pic 8 |

Pic 9 |

Pic 9a |

Now extend the lower line to the edge of the outer circle Pic10 marked in blue.

Pic 10 |

Pic 11 |

Now is the kind of tricky part as you need to put the point of the compasses in to the point where the blue line touches the outer circle and mark off on the rim 3.14 times around the edge. I over estimate and then file off excess later as it is not the easiest of things to judge. Pic12 = 1 mark,

Pic 12 |

now move the compasses to this new mark and mark again. Pic13 =2 marks,

Pic 13 |

again using the new mark move your compasses around and make the third mark Pic14 = 3marks.

Pic 14 |

Now adjust the compasses to 0.14 of the original dimension (use a calculator, so in my example the original is hmmm lets say 16mm so you need to find 14% of 16mm, I googled it is 2.24, so I need to adjust my compasses to 2.24mm) Pic15.

Pic 15 |

Now using the last mark you made to put your point in make your final mark on the outer rim. Pic16 = the 4

^{th}and last mark.Pic 16 |

Pic 17 |

and finally do the same with your very last mark on the outer edge to the same spot where the red lines cross. Pic18 marked in pink.

Pic 18 |

Pic 19 |

All that remains is to cut this out Pic20.

Pic 20 |

This is your template, use rubber solution glue to stick it to your metal and using a tool to score the shape score round the template, cut out your metal form the ring, solder together, true it up on a mandrel or as I do on a little bench anvil which has a rounded pointy bit.

Pic21

Pic 21 |

Pic22.

Pic23.

Pic 23 |

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