🔧 CAD · Advanced · Build Documentation

CAD to Build
Handoff

CAD is only useful if it informs the physical build. This guide shows how to extract a parts list, screw plan, and fabrication notes from your Onshape model — so the build team knows exactly what to make.

1
Handoff
2
BOM
3
Screw Plan
4
Fab Notes
5
Notebook
// Section 01
What a Handoff Is
A handoff is the package of information that moves a design from CAD to the build table. Without it, builders have to keep asking the CAD person questions — slowing down both people. With it, the build can run in parallel with CAD refinement.

The Four Handoff Documents

📋
Bill of Materials
Every part needed, with quantities. Builder uses this to gather parts before touching the robot.
🔧
Screw Plan
Which fastener goes where. Eliminates the “which screw do I use?” question on every joint.
📷
CAD Screenshots
Annotated views with dimensions. Builder references these instead of guessing from memory.
✂️
Fab Notes
Which parts need cutting, drilling, or modification. Prevents fabrication errors.
⏱
How long should a handoff take to prepare? 20–30 minutes if your CAD model is clean and organized. If it takes longer, your model needs better organization — add that to the next iteration. A good handoff lets someone else build the design without asking a single question.
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// Section 02
Bill of Materials
The BOM is a complete list of every part in your design with exact quantities. Build it from your Onshape assembly — count each unique part and how many instances appear.

How to Generate a BOM from Onshape

  1. Open your Assembly in Onshape.
  2. Click Insert → BOM Table (or right-click the assembly root in the feature tree and select “Create BOM”).
  3. Onshape will generate a table of all parts with quantities automatically.
  4. Export as CSV or take a screenshot for your notebook and handoff document.
💡
BOM tip: Group VEX standard parts separately from custom-fabricated parts. Standard parts come from your parts bin. Custom parts need to be cut or drilled. The builder needs to know which is which before they start.

Interactive BOM Builder

Use this to build your handoff BOM during a CAD session. Saves to your device.

📋 Bill of Materials
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// Section 03
Screw Plan
Every joint in a VRC robot uses a specific fastener for a specific reason. Documenting this prevents the most common build error: using the wrong screw in a critical joint.

Fastener Reference — VEX Standard

FastenerThreadBest UseAvoid
8-32 × 0.5” button head8-32Light structural joints, most frame connectionsHigh-load pivots — button head can strip under torque
8-32 × 0.5” socket head8-32All high-torque joints, motor mounts, pivot pointsAnywhere you need to remove quickly — requires hex key
8-32 × 0.75” socket head8-32Through two layers of C-channel plus spacerJoints with only one layer — too long
8-32 × 1.0” socket head8-32Bearing block + c-channel + spacer stacksStandard frame joints — far too long
Nylon lock nut (8-32)8-32Any moving joint, motor mounts, arm pivotsDo not use on field elements or electronics (vibration loosens)
Keps nut (8-32)8-32Quick-disconnect structural joints you need to access in the pitMoving joints — vibrates loose under dynamic load

How to Document the Screw Plan

In Onshape, take a screenshot of each major joint with dimension annotations showing:

These screenshots go in the handoff document and in the notebook. A builder can match the screenshot to the physical robot and assemble the joint correctly without asking.

⚠️
Loctite rule: Apply Loctite Blue (242) to any structural screw that experiences vibration. This includes all drive frame screws, motor mount screws, and arm pivot screws. Mark these on your screw plan with “L”. Never use Red (271) — it is permanent and requires heat to remove.
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// Section 04
Fabrication Notes
Custom parts — gussets, plates, brackets — need to be cut or drilled. Fabrication notes tell whoever is cutting exactly what to make and how to make it right the first time.

What Needs a Fabrication Note?

Custom Plate Design in Onshape

🔄 Step 1 — Sketch
In a Part Studio, create a new sketch on the XZ plane. Draw the plate outline and all holes as circles. Use exact dimensions referenced to the 0.5” VEX hole grid.
🔄 Step 2 — Extrude
Extrude the plate to the material thickness — typically 0.125” for polycarbonate sheet, 0.090” for aluminum sheet. Use “Remove” for the hole extrudes.
🔄 Step 3 — Drawing
Create an Onshape Drawing from the part. Add dimension annotations to every edge and hole. Export as PDF — this is your cutting template and notebook evidence.
🔄 Step 4 — Material
Specify the material in the fab note: “Polycarbonate, 1/8” sheet” or “6061 aluminum, 0.090” sheet.” Cutting method: hand cut with polycarbonate cutter, CNC router, or laser cutter.
⚙ STEM HighlightEngineering: GD&T and Manufacturing Tolerances
Professional engineering drawings use Geometric Dimensioning and Tolerancing (GD&T) — a system for specifying exactly how much a fabricated part is allowed to deviate from the design. A hole position might be specified as ±0.005”. For VRC custom parts, you don’t need full GD&T — but you do need to specify tolerances for critical dimensions. A ¼” bearing bore needs to be ±0.002”. A structural clearance hole can be ±0.030”. Understanding which dimensions are critical is the difference between a part that works and one that doesn’t fit.
🎤 Interview line: “When we design custom gussets and mounting plates, we create Onshape drawings with full dimensions and specify material thickness and cutting method. This documentation means anyone can fabricate the part from the drawing — we’re not guessing measurements during the build.”
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// Section 05
CAD Evidence for the Notebook
Every CAD artifact you produce is potential notebook evidence. Here’s exactly what to capture at each EDP phase so your notebook is CAD-backed throughout the season.

CAD Evidence by EDP Phase

🔎Identify Problem
CAD evidence: Screenshot of the existing design (or a blank field) showing what constraints you are working within. Annotate max size limits, game element dimensions, scoring zone positions. This proves you analyzed the problem before designing.
💡Brainstorm
CAD evidence: Quick concept screenshots of 3+ designs. These don’t need to be polished — rough assemblies showing the core idea are fine. Label each concept with its name and key characteristics. Include the paper sketch that preceded the CAD.
✅Select Best Solution
CAD evidence: Decision matrix screenshot (all three concepts, weighted criteria, scores). Annotated comparison views showing the key differences between concepts A, B, and C. Written rationale referencing specific matrix criteria.
🔧Build & Program
CAD evidence: Final CAD screenshots — top-down, isometric, and detail views with dimensions annotated. BOM screenshot. Screw plan screenshots. Fabrication drawings for custom parts. Compare CAD vs physical build photo — this proves the build followed the design.
🔬Test & Iterate
CAD evidence: Version history screenshots showing what changed between CAD v1 and v2. Annotated comparison views showing exactly what was modified and why. This is the iteration evidence judges score under “Repeat Design Process.”
🏆
The Design Award connection: The RECF rubric’s Expert column requires “multiple detailed diagrams with pros/cons and research backing.” CAD screenshots with annotations are exactly these diagrams. A notebook with 5+ EDP cycles each backed by CAD evidence — concepts, decision matrices, final designs, iteration comparisons — scores Expert in multiple rubric rows simultaneously.

Related Guides

💻
Onshape Setup
Account, documents, VEX library
 🚗
First Drivetrain
Shaft planning, bearing placement
 📝
Engineering Notebook
EDP, rubric, Design Award
 🔬
Testing System
Test what you built from CAD
 ✂️
Custom Parts & Fabrication
DXF, X-Carve, PDF, Delrin, polycarbonate
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