Week 07 – Computer Controlled Machining

Personal and Group Assignment

This week's personal assignment was to document the process of designing and machining a large-scale project. The group assignment focused on testing the machine's runout, alignment, speeds, feeds, and toolpath capabilities.

Group Assignment

Here's also the link to our group assignment of this week.

What is Computer Controlled Machining?

It is a subtractive fabrication process where a computer-controlled cutting tool (a router bit) removes material from a solid block to create a shape. Unlike laser cutting, CNC machining allows for 2.5D and 3D shapes by controlling the depth (Z-axis).

Large Format CNC Workflow

Working with a large format CNC router involves a clear sequence of steps — from digital design to physical part. Each stage depends on the previous one, so understanding the full pipeline is essential before touching the machine.

The process starts in CAD software (in my case Shapr3D), where the part is designed with the final dimensions and joint tolerances already considered. The design is then exported as a DXF file, which is imported into VCarve Pro — the CAM software — where toolpaths are generated and cutting parameters are set.

VCarve exports the toolpaths as a G-Code file, which is loaded into Mach3 — the machine control software that communicates directly with the CNC router. Before running the file, the machine must be physically prepared: the material is secured to the bed, the correct bit is installed, and the X, Y, and Z origins are set precisely using the control panel and a Z-probe.

Once the machine runs, the operator must stay present at all times to monitor the cut, check for material movement, and stop the machine immediately if something goes wrong. After machining, the parts are sanded, deburred, and tested for fit before final assembly.

Full workflow summary

01. Design — Model the part in CAD (Shapr3D) with correct dimensions and joint tolerances. Export as DXF.

02. CAM setup — Import DXF into VCarve Pro. Define toolpaths (Profile, Pocket, Drilling), set feeds, speeds, and depth of cut. Run a simulation to verify.

03. Machine preparation — Mount and secure the material. Install the correct router bit. Set X/Y origin at the material corner. Use the Z-probe to zero the Z axis.

04. Cutting — Load the G-Code in Mach3 and start the cut. Monitor continuously. Never leave the machine unattended.

05. Post-processing — Sand edges, remove burrs, test press-fit joints, and assemble.

CNC Tooling and Bits

Choosing the right tool is essential for a good finish and machine safety. These are the most common bits I used:

Up-cut

Pulls chips upward. Excellent for clearing material in deep cuts but can leave a rough finish on the top surface of the wood.

Down-cut

Pushes chips downward. It provides a very clean top surface finish, ideal for shallow engraving or thin materials.

Compression

Combines up-cut and down-cut geometry. It leaves a clean finish on both the top and bottom of the material, perfect for plywood.

Machine Specifications

Before machining, I reviewed the technical specifications of our machine to set the correct feeds and speeds in VCarve.

This is the large-format CNC machine at Fab Lab Puebla.

Feature	CNC Router
Work Area	1220 x 2440 mm (4' x 8')
Spindle Speed	Up to 18,000 - 24,000 RPM
Materials	Plywood, MDF, OSB, Foam, Soft metals
Hold-down	Vacuum table / Nails
Axis	X, Y, Z (3-Axis)
Post-Processor	G-Code (Arc/mm)

CAM Process in VCarve

To convert my 2D design into machine instructions, I used VCarve Pro. This is the workflow I followed:

Strategy	Application	Parameters
Profile	Cutting out the external shapes	Outside vectors, add Tabs
Pocket	Creating hollows or recesses	Inside vectors, clearing path
Drilling	Pre-drilling holes for screws	Center of circles, Peck drilling
Dog-bones	Corner clearance for joints	Corner fillets for 90° fit