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Machining centre automates the setting of gemstones
Machining centre automates the setting of gemstones

Machining centre automates the setting of gemstones

Added to MTDCNC by Whitehouse Machine Tools on 01 December 2015

An ingenious method for automating the setting of gemstones has been developed using a Brother 30-taper, vertical machining centre, which can naturally also carry out high-precision milling of gold, silver and other precious metals. The Japanese machine builder’s sole UK agent, Whitehouse Machine Tools, describes the metalforming process.

Traditionally, the metal that holds a gem in place is formed manually over the crown of the stone to create the setting. When only one or a few stones are secured, in a ring for example, this is still the easiest way. However, a clasp for an expensive handbag can easily hold a matrix of 250 diamonds over a flat surface. In this case, considerable time savings can result from automating their setting.

It has been found that a Brother vertical-spindle machining centre can be used to set the gemstones in a CNC cycle. The metalforming technique involves slowly rotating a steel tool with a hollow dimple at the tip, slightly larger than the gem, and programming it to visit each stone consecutively and press the metal over the crown to create a rim setting.

Alternatively, to produce a pavé setting that looks like a continuous surface of many closely-spaced diamonds, a similar but smaller diameter tool bends the metal into beads around each stone to hold it in place.

In both cases, the time for completing the setting cycle is a fraction of that needed to do the job manually, so the customer receives the item in a shorter lead-time. Repeatability is better than is possible to achieve by hand, resulting in even higher quality products. If a twin-pallet, 3-axis Brother TC-31A is used for this purpose, four clasps may be fixtured on the two pallets and set with diamonds unattended overnight.

If engraving on a curved surface is required, production can be transferred to a Brother machine with a 4th axis rotary indexer. A 60,000 rpm air turbine may be deployed in place of the Brother spindle to raise productivity, but for most jobs the TC-31A’s 22,000 rpm spindle is sufficiently fast.

5-axis machining in jewellery manufacture

A Brother machining centre ideally suited to milling precious metals is the 5-axis TC-S2 DN -O, which has a 27,000 rpm spindle and 2-axis compound table. The machine is able to transform the metalcutting possibilities available to a jewellery producer. For instance, complex cutlery handles can be fashioned from solid silver in a 3+2-axis cycle for economical production in significant batch sizes.

In addition to machining end products, hardened steel tools for pressing products such as phosphor-bronze pen clips may also be produced on Brother machining centres.

Swarf reclamation and recycling is a priority in jewellery manufacture in view of the high value of the metals used. Boxes placed under the workpiece in each machine catch 80 per cent of the swarf. The machining centres are usually cleaned down after completing each production batch and the remaining precious metal dust is retrieved from a fine filter, after it has been left to dry. In this way, over 98 per cent of swarf is reclaimed.

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