The eMachineShop CAD software intentionally limits what you can design to shapes that can be manufactured by certain manufacturing processes using standard economical methods. To understand what shapes are possible it helps to understand one of the key processes, milling, on which much of the user interface is based. Although eMachineShop uses CNC milling, a picture of a manual milling machine is easier to understand:
A milling machine looks somewhat like a drill press at first glance. A cutting tool protrudes down from a rotating spindle. A block of material is placed on a moving table below the cutter. While the cutting tool turns, a computer controls the vertical (Z axis) motion of the cutter and the horizontal (X and Y axis) motion of the block of material. The cutter is guided to move through the material, removing portions to create shapes. Additionally, the material can be turned to various orientations in the middle of the process and cutting tools of various shapes can be used. The cutter shapes directly supported in the CAD include (shown in side view):
The above tools are essentially round when viewed from the top. Referring to the above images from left to right:
- Plain endmill – used for most milling – creates walls with straight 90 deg edges and sharp corners at the bottom of recesses.
- Chamfer endmill – creates 45 deg bevels on the top (near) edge of a wall or recess
- Grooving endmill – creates rectangular grooves in side walls
- Ball mill – creates rounded edges at the bottom (far) edge of a recess
- Rounding endmill – creates rounded edges at the top (near) edge
- Angle endmill – creates walls at angles other than 90 deg
- and, not shown, a conventional drill
The eMachineShop CAD limits shapes to those that can be made by motion of the cutters vertically or X/Y motion of the material along straight lines or curves, but not simultaneous motion of all 3 axis, as doing so generally increases costs substantially and significantly complicates the interface. Knowing these capabilities and limitations allows you to determine what is possible and insures that the parts you design will be economical to make.
Many more shapes are possible using the revolve feature which is the basis for turning parts on a lathe or turning center.
Examples of possible shapes include the parts shown on various pages of this web site such as the main gallery. You will see that a quite diverse array of shapes are possible.
Examples of shapes that cannot be modeled include those with complex curves such as statues, faces and computer mice, although there are tricks to achieve some complex curved shapes. It is also impractical to mill recesses that cannot be reached, such as a bore on an inside wall of a five side box.