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Imagine a rectangular billet of material on the mill table.

Look at the top, front, left-hand corner of the billet.

However you create your NC code, manually, with AlphaCAM or with other software, always have the co-ordinates of that corner as X=0, Y=0, Z=0. (There are useful exceptions to this rule: see the topic Setting the Origin for Machining)

This corner is the work origin. When you prepare the mill for machining, WELmill guides you through a routine to locate this work origin on the billet. All machining moves are calculated from that corner (ie absolute measurement is used, not incremental). Its location means that all X and Y moves have positive values. All Z moves have negative values, because the end of the tool goes below the Z zero level.

In AlphaCAM or other CAD system, when planning 2.5D machining, always start by drawing a rectangle to represent the billet of material from which the part is to be cut. On the PC screen, the bottom left corner of the rectangle must at X=0, Y=0. The exact location of the geometry of the part within the billet boundary does not matter: all tool movements are calculated from X=0, Y=0.

When tool paths have been set, tell AlphaCAM that the rectangle is the boundary of the billet. To do this click on 3D

3D Simulation to see what will happen when the part is machined.

                              

In AlphaCAM, if creating or importing 3D geometry, this geometry will be enclosed in a Work Volume. This is not the billet: it is an envelope which contains the geometry. The billet needs to be defined separately. To do this, draw a rectangle of suitable X and Y dimensions round the X-Y plan of the geometry. The X and Y dimensions need to be bigger than the greatest X and Y dimensions of the part by at least the diameter of the largest cutter which is to cut round the outside of the part. Ensure the rectangle has positive dimensions from X=0, Y=0.

Now click on 3D