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Milling machine – how to make… – silver box

When jewellers make silver boxes they do not use the conventional folder. This gives slightly rounded corners and truly square corners look much better.

The box is made out of one piece of metal. Where the folds are the sheet is cut forming a v-shape cut.

This is done using a double-sided 45° cutter on a horizontal arbor (in the horizontal socket).

Thin sheet is seldom really flat so, ideally, the sheet is clamped all along points where it is to be machined. In practice the cutter is not big enough to be able to clamp the workpiece on top. Though the cuts are not meant to go all the way through, the workpiece is mounted on parallels but even these are not directly under the cut.

This is used to machine along all the inside edges of the box where they are folded but not right through the sheet of silver. For a rectangular piece of silver sheet this needs two cuts along the x-axis and two along the y-axis.

Small differences in flatness will make relatively large differences in the thinness at the thinness part of the V’s.

 

Fig. Machining a “silver” box 444

 

For a copper sheet which is 2mm thick the V’s need to be about 1.75mm deep so the part that is actually folded is only 0.25mm thick. This can easily be folded using the finger without any difficulty.

But, before folding, it is essential to clean up the V’s with a fine file. Small pieces of copper swarf can easily get welded on and these will stop the sheet being folded to a perfect 90º.

A fold like this can only be done once, undone once and folded, if necessary, again for the second time before the joins break completely.

The corner pieces that are not needed can be sawn diagonally and can then be broken off by bending then to and fro.

The box is folded and the corners and edges are then soldered with silver solder.

see Solder and soldering for silver solders to be used if the object is to be hallmarked.

(If the material is thin it might be difficult to silver solder it without is distorting but it could be soft soldered easily.)

It is possible to machine the edges of the box using a slitting saw whilst the work piece is set up to mill the V-shapes. But it is unlikely that the edges will all be the same height. So the soldered box is clamped to the milling table and the tops of the sides milled so they are all the same height.

(For reasons the reader will probably appreciate, copper has been used in the example).

ref

The Theory and Practice of Goldsmithing

E Brepohl

p220