Carving on Acrylic sheet using CNC-machine

Carving is a subtractive manufacturing/machining process in which the tool scrapes out the material from the workpiece to generate the desired shape object. The process has been here for centuries; sculptures made of stone or paintings inside the caves are examples.

Advancement in Computer-Aided Manufacturing (CAM) has modernized the traditional carving process. Nowadays, Computerized Numerical Control (CNC) machining eliminates the need for sculpting skills to carry out the machining process like carving. A CNC router is a computer-controlled cutting machine which is having a cutter attached to a rotating spindle to carry out the cutting process; the tool attached with the spindle is guided on the workpiece to remove specific material at certain locations.

Typically, the CNC- router used for carving woods, aluminum, and plastic has 3 DOF in a Cartesian coordinate system. The router can carry out translational motion in the X, Y, and Z-axis.

Working with Acrylic

Let us come to the central part, i.e., how to carve on acrylic? The complete process can be divided into three significant chunks.

1. Pre processing – In first stage, we will take the geometry and will generate the corresponding G-code based on the required finishing and machine characteristics.
2. Processing – In this stage, the actual cutting process is carried out.
3. Post-processing – In this stage, the additional finishing operation using sand papers and polish is carried out.

Pre – processing

This stage is the most straightforward yet crucial stage of the whole process. First, we will import the geometry (.obj, .stl) format in any standard CAM software (Autodesk Fusion 360). Then, we will set up the dimension (this includes modifying the measurements based on clearances and clamping zones) of the workpiece and starting position.

Then, we can specify the type of clearing process (Adaptive or pocket clearing) and machining parameters (such as feed rate, depth of cut and plunge rate, etc.). The machining parameters are crucial in the whole process; a wrong combination can damage the workpiece and the tool.

The following combination of parameters can work well –

After the roughing operation, we can select the finishing operation and corresponding machining parameters. Majorly, the machining parameters remain the same except for the depth of cut and similar parameters.

Processing

After the G-code is generated, the workpiece is set on the bed of the CNC router. The clamping should be done so that it restricts the movement of the workpiece in all three directions. The clamps should be carefully kept so that they don’t come in the tool path specified in the G-code.
The presence of chips (material removed by the machining process) on the workpiece can affect the surface finish of the final object. If the chip removal system is not integrated with the machine, we should manually remove the chip.

Post processing

Up to this point, the surface of the workpiece may have marks generated by the tool, which can make the surface translucent. So, wet sanding is done to remove those marks. Wet sanding is basically a sanding operation done in the presence of water. It should be done with 220, 400, 600, and 1500 grit sandpaper one by one. The sanding should not be restricted to one location and should be done with light to medium pressure. After the wet sanding, standard glass polish can be applied to further enhance the surface finish.

Hurray !! You have got the final object.

One problem that I faced when feeding the G-code in the CNC software was – “Your design exceeds the work area bounds. Make your design smaller and try again.” Even after the scaling down the geometry multiple times, the error persisted. Later on, I realized the issue was not with the geometry but with the setup. The geometry must always be in (+,+,+) cartesian zone i.e. first zone.