As jewellery moves forward through the technological age, more and more jewellers are choosing to use CAD software to create pieces. There are many benefits to using CAD, especially one with a rendering package. It allows you to develop a design and make changes whilst creating. In the past, you would need to draw multiple sketches and create test pieces if unsure about a design, This can be quite a long and expensive process. However, with CAD you are able to see what a piece will look like once finished, even before you pick up a buff stick.

There are downsides to CAD if you are a first time user. What looks great on your computer screen may not be what you expect when you receive it back from the rapid prototypers. There are some simple steps which, if you keep in mind, will make your experience of getting something made go much smoother.

First, it’s always good whilst designing a piece to keep a rule or vernier gauge to hand. Pieces can seem a lot bigger on the screen and elements can appear to be a lot thicker. It’s always tempting to make an element thinner or smaller; too often people fall into the trap of believing their piece looks chunky, but when zoomed in, 1mm can seem massive. The minimum recommend thickness is 0.8mm and it is wise to stick with this. If you do want to go smaller make sure the element is supported by other sections of the design. Contact points between a smaller element and a thicker one will give you a better chance of the rapid prototype surviving. On a similar note, remember the piece you receive back after casting will need to be cleaned up. So after you have filed, buffed and polished, metal will be lost so something less than 0.8mm can quickly turn into a very fragile piece.

Secondly, it’s always good to consider sprues whilst designing. Your piece will be made on a platform and there will be multiple supports created while the piece is built. However, once it is a resin model, your caster or the caster used by your rapid prototyper, will need to add a sprue for the piece to be cast. If you’re lucky, the sprue will be placed in a position which is easy to clean. However, there is always a chance it could be put in a less desirable place. Once your model is complete in your CAD software, just add a long cylindrical bar. I recommend this to be no thinner than 1mm (thicker is better though) and at least 20mm long. Your caster can cut this down while still in resin but it just makes sure you don't have any unwanted cleaning to do. Also, this would mean a neat join which is easier to clean up than if the join is done with wax.

Thirdly , if you haven't seen a model which has been rapid prototyped before, be prepared for stepping and a bumpy texture in place where the original supports were. Rapid prototyping is done in layers and with a very tiny system of supports. Depending on how fine the layers have been set can alter the appearance, but on a smooth curve tiny steps can be noticeable. These can be buffed off. If you are creating a piece which has large solid curves it’s always wise to make the thickness 0.1 - 0.2mm bigger than needed so you have metal to move. It’s easy to remove metal but near impossible to put it back.

Finally, in most cases your file will need to be saved as an STL model file. Before sending your piece, it’s always good to do a check that there are no hidden elements in other layers and that everything is joined together. If you have access to an analysis software package, it’s good to run your model through it to double check there are no problems and also double check the size one last time. If you are unsure about a model, it’s always worth talking to your rapid prototying company first. They will offer advice and inform you on anything that possibly won’t work before you go ahead.

Mainly I recommend exploiting the possibilities. Rapid protoyping opens us up to a whole world of creativity which would have once been impossible, so as long as you consider the size, clean up and double check, you should be issue free.

Author: Rhianne Hutchinson - Part time lecturer at BCU Birmingham Jewellery School and laser technician at GETi

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