What is a frustum? A frustum is a cone or truncated form. In jewelry it is used to make a tapered collet for a bezel or prong for a faceted stone. It can also be used for other decorative applications.

Creating a frustum can be frustrating and confusing to say the least. There are so many different formula’s or techniques each one just a little different from the last.

When I read the directions in the Complete Metalsmith by Tim McCreight (which is a book that I love ), I have to admit it left me perplexed. The technique he uses involves trying to use a string to create the connections of points but it just doesn’t give me the accuracy that I am looking for. Plus it lacks some important details about which points I am placing the string at.

Complete Metalsmith image Making a cone pattern

You can make a straight bezel and use a bezel block to form the collet but what I run into with this technique is that because I make my work chunky and use a heavier gauge for my collet there can be a lot of metal to move on the bottom of the bezel which can make it lopsided if you don’t hit it exactly right. This technique can good for thinner gauge metal for small stones.

I use the following formula that I found in facetjewlery.com which I am sharing below, but of coarse I have my own little insight that I like to share. I follow the layout all the way to step 4. However these instructions are similar to complete metalsmith in recommending that we use a string or a wire to find the distance.

How to Make a Frustum by facetjewelry.com

But they do give you a great tip! I like it to because it is more accurate, I follow the note that is provided and skip steps 5 and 6. I do not add on the 14%. (unless it is a larger cone form, for a part I am building not a setting.) I feel that the thickness of the pencil lines or maybe it is just my heavy hand, it winds up too big when I add on the 14%.

After I have my frustum laid out on paper I rubber cement it to my metal and saw. I use round needle nose pliers to form the cone and solder with hard. I still use the bezel block to help shape the form to the exact size for my stone.

We all know that there are many ways to get to where we are going and I hope these tips help you get there quicker. I have to say no matter which directions I have gone to get there my favorite part about the whole process is when you get to see that metal move and form into that perfect little cone. So satisfying.

Frustum or Frustration?