CNC Basics & 3D Printing

Copy the Document

As before, start by copying the tutorial document to your own Onshape account.

A. The Magic of CNC

CNC lets computers control machines to automatically manufacture parts

What is CNC?

CNC = Computer Numerical Control. In simple terms, it uses a computer to control a machine that automatically manufactures parts. You design the part in Onshape, then let the machine produce it precisely according to your design.

Common CNC Tools

• 3D Printer — Builds parts layer by layer with material (this chapter's focus)
• Laser Cutter — Cuts flat materials with a laser beam (Chapter 14)
• CNC Mill / Router — Removes material with a rotating cutting tool (Chapter 15)

These tools allow robotics teams to manufacture precise custom parts — shapes you can't buy off the shelf, special mounting brackets, or structural components that perfectly match your design.

B. What is 3D Printing?

3D printing builds parts by depositing material layer by layer

How 3D Printing Works

3D printing (also called additive manufacturing) creates parts by depositing material layer by layer (usually plastic filament like PLA or PETG). The printer's nozzle heats the filament to melt it, then lays it down one layer at a time following the designed path.

Why Do Robotics Teams Use 3D Printing?

• Rapid prototyping — Turn a design into a physical part within hours; test ideas quickly
• Custom parts — Manufacture specialized parts you can't buy commercially
• Complex shapes — Create shapes that are difficult or impossible with traditional machining

Common Uses

• Motor mounts and sensor brackets
• Gearbox housings
• Gripper components
• Cable management clips

Prototyping Examples

Many top robotics teams use 3D printing for rapid prototyping:

• Spectrum #3847's Prototyping Blocks — Standardized 3D-printed building blocks for quick prototyping
• HYPE #5254's HYPE Blocks — A similar modular prototyping system
• Quick Build Clamping Blocks — Printed blocks for quick clamping and fixturing
• Protopipe — A prototyping method using 3D-printed connectors with tubing

C. Designing for 3D Printing

Consider print orientation, supports, and wall thickness when designing

The Printing Workflow

The complete workflow from CAD model to physical part:

1. CAD Model — Design the part in Onshape
2. Export STL — Convert the model to 3D printing format
3. Slicer Software — Use Cura/PrusaSlicer to "slice" the model into layers
4. G-code — The slicer generates instructions that control printer movement
5. Print — The printer follows the G-code to print layer by layer

Designing for Strength

3D-printed parts have an important characteristic: print orientation affects part strength. The bond between layers is the weakest link.

Key Features

• Overhang angle — Overhangs less than 45 degrees from vertical don't need support structures
• Holes — Holes printed vertically come out rounder and more accurate
• Wall thickness — At least 2mm; walls that are too thin will break easily

Embedded Nuts and Heatset Inserts

3D-printed parts often need to connect to other parts. Tapping threads directly into plastic strips easily, so a better approach is using embedded nuts or heatset inserts.

Pause the print mid-way, insert a nut, then resume printing — the nut gets embedded in the part

XZ/YZ plane embedded nuts: design a hex slot for the nut to slide in, and the print wraps around it

Heatset inserts: heat with a soldering iron and press into a pre-made hole for reliable threaded connections

Supports and Infill

• Less support is better — Support structures increase print time and material use; they also leave rough surfaces after removal
• Infill percentage — 20-50% is usually sufficient. 100% infill wastes time and material, and makes the part heavier

D. Exporting STL from Onshape

Right-click part → Export → Select STL format

Export Steps

Right-click a part in Onshape → Export → Select STL format

1. Right-click the part you want to export in the parts list
2. Select Export
3. Choose STL as the format
4. Settings: Select Binary STL (smaller file size) and Fine resolution (more detail)
5. Click export and save the file

Exporting Multiple Parts

If you need to print multiple parts, you can export them one by one or select multiple parts to export together. We recommend exporting individually so you can adjust print parameters separately in the slicer.

Importing into Slicer Software

Import the STL file into slicer software, configure settings, and generate G-code print instructions

The exported STL file needs to be imported into slicer software (like Cura or PrusaSlicer) to generate print instructions. Common slicer settings:

• Layer height — 0.2mm for general use / 0.12mm for fine detail (thinner layers = finer quality but longer print time)
• Infill — Choose 20-50% based on the part's purpose
• Supports — Enable when there are overhanging sections
• Speed — Slower = better quality, but longer print time

E. 3D Printing Troubleshooting

Common 3D printing problems and solutions

Elephant's Foot

The bottom of the print bulges outward, looking like an elephant's foot. This happens when the first layer temperature is too high or the print bed is too close to the nozzle.

• Lower the first layer temperature
• Increase the Z-offset (move the nozzle slightly farther from the bed)

Stringing

Fine strings appear between parts. This is caused by material oozing from the nozzle during travel moves.

• Enable retraction
• Lower the print temperature slightly

Poor Bed Adhesion

Parts detach from the build plate during printing.

• Level the print bed
• Use a glue stick or PEI print surface for better adhesion

Warping / Melting

Parts warp or fine details melt.

• Lower the print temperature
• Increase cooling fan speed