Section: 3D Advanced
This section covers the more advanced 3D drawing methods. You might want to skip this section and return later if you are new to eMachineShop.
Complex 3D curves are curves that require machining motions on all three directions simultaneously. For example the top of a computer mouse is a complex 3D curve. You can create complex 3D curves in the eMachineShop CAD only by approximating shapes using a stair-case approach as in a topographic map as in the example below:
- Use the Line | Contour command and manual adjustments such as by nudging to create the contour lines.
- Set the Z value for each line.
- Consider using Comments to Machinist “Hand sand to remove steps” or “Contour mill to remove steps”.
Also see the Revolve capability which allows for complex “turned” curved shapes.
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:
Milling Machine and Endmills
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):
Those tools drawn in pink are essentially round when viewed from the top. Referring to those 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.
An angled wall is one at an angle other than 90 degrees. You can create angled walls on outside or inside shapes. For example, you might want a tapered wall inside a round hole or when designing injection molded or cast parts, you may need to use walls of about 92 degrees to allow your part to be easily removed from the mold.
To set the angle of a wall
- Choose a line in your drawing.
- Set Line | Machine | Auto | Side Wall | Angle to the desired angle.
- Click OK.
Sharp Inside Corners
You might need a rectangular hole (or any sharp corner shape) into which you will slide a rectangular male item (e.g. a power switch). If you draw a simple rectangle you might receive a warning that the corners will be rounded which could block insertion of the rectangular item. In this case consider creating a shape like this:
To create a mating shape (like the image above to the right)
- Draw the shape of the male component.
- Select Line | Corner | Mate | Inside.
- Enter the desired radius – it is recommended to use the largest acceptable radius.
- Click OK.
- Increase the size of the female shape slightly for clearance and tolerance using Line | Contour | Outside.
- Draw a rectangle.
- Draw a circle of the desired corner diameter – say .25″. Typically you can use the Minimum Cutter Diameter value.
- Click the Repeat button three times.
- Drag the circles so that their top snap points snap to each corner of the rectangle.
- Rotate each circle around the rectangle’s corner the appropriate multiple of 45 degrees.
- Select everything.
- Choose Line | Intersect.
- Delete the interior segments.
- Group the line segments.
- Set Z to Air Inside.
Why not sharp corners?
Sharp inside corners are problematic because most cutting processes use round tools. Round cutting tools can make sharp outside corners and sharp corners at the bottom of a pocket but not at the corners of the walls of a pocket. Imagine taking a block of ice and creating a square pocket (recess) with a round hot metal rod – you can’t get sharp corners at the walls of the pocket because the rod is round. For 2D processes (cutting sheets) tools are often very thin so you can get close to a sharp corner. For 3D processes tools of small diameter can be used but they usually cannot reach deeply as they will break.
Note: 3D shapes that cannot be modeled directly in the CAD can often be described using the Comment feature.