Thursday, October 11, 2012

Amulet Construction

To make the amulet shown below in CAD drawings I first start with a piece of 360 brass stock.  It is held to the plate below with a layer of paper and wax based adhesive.  This can be applied or removed with just over 200 degrees fahrenheit, easily supplied by a hot plate.  This has the advantage of not having to be pried off like double stick tape.  It allows you to cut all sides of the part free without additional clamping.

The first program cuts the outside of the amulet profile and the center pocket for the gem.  This cut is made with a square end mill.

The second program roughs out the 3 dimensional contours of the part.  I use a 1/8" diameter ball end mill.  It leaves a minimum of .007" of an inch everywhere on the part to allow for a finish cut.  This cut took approximately 20 minutes to make, and removed the bulk of the material.  Although the cut is shiny, the detail does not match the model very closely.

The finish cut is made with a 3/64" ball end mill.  The tool moves in a spiral from center to outside. Each  arm of the spiral is .0015" apart.  It moves up and down at the same time to form the contours of the part.  This cut takes much longer to make (~2hrs) but produces the fine finish seen here.  The part and plate it was resting on were returned to the hot plate and separated.  

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