Read orthographic views, scales, dimensions, tolerances, schematics, GD&T callouts and floor plans, then sketch and model parts in free CAD tools.

Technical Drawing & CAD Basics

Measure the object's overall width, depth and height with a tape or ruler and write them down with units.

Measure two or three features (a hole, a notch, a step) and their locations from an edge.

Choose the front view and lightly block in the front, top (above) and right side (to the right) views on grid paper, keeping them aligned.

Project each feature between views with light lines, then add hidden lines and centre lines.

Darken the visible lines so they are clearly thicker than hidden and centre lines.

Add the key dimensions, each feature once, on the view that shows it best.

On a separate area or sheet, sketch an isometric view of the object, boxing it in first and drawing any holes as ellipses.

Add a small title block: part name, your name, date, units, NOT TO SCALE and third-angle projection.

Show your sketch to someone else and ask them to describe the object without seeing it. Note anything they got wrong.

## Why it matters

Even in a world of CAD, the fastest way to explain a part, a bracket you need, or a conduit route is a quick sketch. Engineers sketch in design meetings, electricians sketch as-built changes, and mechanics sketch a worn part before it goes to the machine shop. A clear sketch with the right views and a few key dimensions can save hours of back-and-forth.

## What you need

- Pencil (a mechanical 0.5 mm works well) and an eraser.
- **Grid paper** (5 mm or 1/4 in squares) for orthographic sketches, and **isometric grid paper** if you have it (free printable sheets exist online).
- A ruler for checking, though good technical sketches are freehand.
- The part itself, or a picture of it, and a tape or caliper to measure it.

## Freehand line technique

- Draw lines with your arm, not just your wrist. Mark the start and end points first, then sketch light strokes between them.
- Pull lines toward you or across, rotating the paper if needed.
- Sketch **light construction lines** first; darken the final outline at the end.
- Use **line weight** to communicate: dark, thick visible lines; medium dashed hidden lines; thin centre and dimension lines.

## Proportion over precision

A sketch does not need to be to scale, but proportions should be right. Use the grid: if the part is 60 mm by 40 mm, make it 12 squares by 8 squares on 5 mm paper. Estimate features by halves and quarters of a known length.

## Sketching three views: step by step

Use third-angle projection (US convention) unless told otherwise.

1. **Choose the front view**: the face that shows the most shape.
2. **Block in the front view** as a light rectangle using the overall width and height.
3. **Block in the top view** directly above, the same width, using the depth for its height. Leave a gap of a few squares.
4. **Block in the right side view** to the right of the front, the same height, using the depth for its width.
5. **Project features between views** with light horizontal and vertical lines. A step in the front view appears as a line in the top and side views.
6. **Add circles and arcs**: sketch the centre lines first, mark the radius on each line, then join the marks.
7. **Add hidden lines** for features you cannot see.
8. **Darken visible lines**, then add centre lines.
9. **Add key dimensions** with extension and dimension lines, once each, on the view that shows the feature best.
10. **Add a title block**: part name, your name, date, units, "NOT TO SCALE" if it is not.

## Sketching an isometric view

1. Draw three light axes from one corner: one vertical, two at 30 degrees from horizontal (follow the isometric grid).
2. Mark the overall width, depth and height along the axes and box in the part.
3. Cut away notches and steps from the box.
4. For holes, sketch **ellipses** on the faces (a circle in isometric is an ellipse). Box the ellipse first in a rhombus.
5. Darken the visible edges only. Isometric sketches usually leave out hidden lines.

## Worked example: a small angle bracket

A bracket is an L shape seen from the front: 50 mm wide base, 40 mm tall upright, 5 mm thick, 30 mm deep. Two Ø6 holes go through the base, 12 mm in from each end.

- **Front view (12 × 8 squares at 5 mm, close enough):** the L outline. The base holes appear as hidden lines.
- **Top view:** a 50 × 30 rectangle with a line 5 mm from the left end where the upright rises, and two circles with centre lines on the base.
- **Side view:** a 30 × 40 rectangle with a line 5 mm above the bottom for the base thickness.
- **Dimensions:** overall 50, 40 and 30; thickness 5; hole locations 12 from each end, centred in depth; 2X Ø6 THRU.

## Common mistakes

- Starting with details before blocking in the overall size.
- Views that do not line up, so features cannot be projected.
- All lines the same weight.
- Dimensioning the same feature in two views.
- Forgetting units.

## Recap

- Sketch light, then darken; use line weights to separate visible, hidden and centre lines.
- Block in all three views first, aligned, then project features across.
- Use grid paper for proportion; circles in isometric become ellipses.
- Add key dimensions once each and a simple title block.

## Try it

The **Do** tab walks you through sketching a real object from your home in three views and an isometric view.


Sketch a simple part in three orthographic views and an isometric view using paper and a ruler.

Sketching by hand

Manual Drafting: Orthographic Sketching on Grid Paper

Sketching Multiviews and Dimensions

Download and install LibreCAD from https://librecad.org/ or FreeCAD from https://www.freecad.org/ (official sites only).

Create a new drawing and set the units to millimetres.

Create layers for outline, centre lines and dimensions with different line types or weights (in FreeCAD Sketcher, skip layers and use construction lines for centre lines).

Draw the 120 x 80 mm outline starting at the origin, using typed coordinates or lengths, not the mouse alone.

Draw four 8 mm holes 10 mm in from each edge and a 30 mm hole in the centre. In FreeCAD, constrain the sketch until it reports fully constrained.

Add dimensions: overall size, hole locations, 4X Ø8 THRU and Ø30 THRU.

Add a simple title block with part name, your name, date, units, scale and projection.

Save the file (DXF or FCStd) with a revision letter in the name and export a PDF.

Open the PDF and check every dimension against the reading. Fix any mistakes.

## Why it matters

Almost every engineering and trade drawing you will see is made in CAD (computer-aided design). Industry tools such as AutoCAD, SolidWorks, Revit or Inventor are expensive, but the core ideas (precise coordinates, layers, snaps, dimensions, title blocks) are the same in free software. Learning them now means your first week with a commercial package is about where the buttons are, not how CAD thinks.

## Free tools for 2D drawing

- **LibreCAD**: free, open-source 2D CAD for Windows, macOS and Linux. Closest in feel to classic AutoCAD 2D drafting. Saves DXF, which most CAD tools open.
- **FreeCAD**: free, open-source 3D modeller with a **Sketcher** workbench for constrained 2D profiles and a **TechDraw** workbench for making 2D drawings from 3D models. Better if you want to continue into 3D (lesson 9).
- **Onshape free plan**: browser-based, no install. Free-plan documents are **public**, so never put school, employer or client designs in it.

Download only from the official sites: https://librecad.org/ and https://www.freecad.org/. Checked on 2026-10-23.

## How CAD differs from drawing on paper

1. **You draw at full size.** A 120 mm plate is drawn 120 mm long. Scale is applied only when printing or placing the drawing on a sheet.
2. **You enter exact values.** Type coordinates or lengths instead of eyeballing. LibreCAD accepts absolute coordinates like `0,0`, relative ones like `@120,0`, and polar ones like `@50<90` (50 units at 90 degrees).
3. **Snaps** lock the cursor to endpoints, midpoints, centres and intersections, so lines meet exactly.
4. **Layers** separate content (outline, hidden, centre, dimensions, title block), each with its own line type, colour and weight. Turn layers on and off to simplify.
5. **Dimensions are associative**: they measure the geometry, so if you edit the geometry the number updates. Never type over a dimension value to "fix" it.
6. **Constraints** (FreeCAD Sketcher, Onshape) hold relationships such as horizontal, equal, tangent and fixed lengths. A fully constrained sketch cannot change accidentally.

## Worked example: a mounting plate in LibreCAD

Target: a 120 × 80 mm plate with four Ø8 holes, each 10 mm in from both edges, and a 30 mm diameter centre hole.

1. **Set units:** Options > Current drawing preferences > Units: millimetres.
2. **Create layers:** `outline` (continuous, 0.5 mm), `centre` (CENTER line type, 0.25 mm), `dims` (0.25 mm).
3. **Draw the outline** on `outline` with the Line tool: `0,0`, then `@120,0`, `@0,80`, `@-120,0`, then close back to `0,0`. (Or use the rectangle tool from `0,0` to `120,80`.)
4. **Draw the corner holes** with the circle (centre, radius) tool: centres at `10,10`, `110,10`, `110,70`, `10,70`, radius 4.
5. **Draw the centre hole** at `60,40`, radius 15.
6. **Add centre lines** on the `centre` layer through each hole.
7. **Dimension** on the `dims` layer: overall 120 and 80; hole locations 10 from each edge (or baseline dimensions from the lower-left corner); `4X Ø8 THRU`; `Ø30 THRU`.
8. **Add a title block**: a rectangle in the corner with part name, your name, date, units (mm), scale (1:1), third-angle symbol or note, and general tolerances.
9. **Save** as DXF and **export or print to PDF**.

In FreeCAD the same plate is a Sketcher profile: draw a rectangle and five circles, then apply constraints (horizontal/vertical distance, radius, symmetric) until the sketch turns fully constrained (FreeCAD shows it in a different colour and reports zero degrees of freedom).

## Good CAD habits from day one

- Start at the origin and keep it meaningful (a corner or a datum).
- Use snaps; never guess a line onto another.
- Put everything on the right layer.
- Save often and use clear file names with revision letters (`plate-120x80_revA.dxf`).
- Check the PDF at 100% before sending it.

## Common mistakes

- Drawing in inches when the part is in mm (or the reverse); set units first.
- Lines that look joined but overlap or leave tiny gaps (zoom in and check, or use snaps).
- Typing over dimension text.
- Putting dimensions and geometry on the same layer.
- Uploading private designs to a public free-plan workspace.

## Recap

- Draw at full size with exact coordinates, snaps and layers; scale only at print time.
- Dimensions are associative; constraints lock design intent.
- Free tools: LibreCAD for 2D, FreeCAD Sketcher/TechDraw, Onshape free plan (public documents).

## Try it

In the **Do** tab, install a free tool and draw the mounting plate from the worked example.


Draw and dimension a simple plate in free 2D CAD software and export it as a PDF.

Your first 2D CAD drawing

LibreCAD - Lesson 01 - Introduction, Download, Install, Interface, Panels, Toolbar, Customize, Reset

FreeCAD Beginner Tutorial : Sketch

Create a free Onshape account (no payment needed) or install FreeCAD from https://www.freecad.org/, and start a new part in millimetres.

Sketch the L profile on the front plane starting at the origin, add the dimensions 50, 40 and 5, and constrain it fully.

Extrude (Pad) the profile 30 mm, symmetric about the sketch plane.

Sketch two 6 mm circles on the top face of the base, 12 mm from each end and centred in depth, and cut them through all (or use the Hole feature).

Add an R3 fillet to the inside corner of the L.

Rename the features in the tree so another person can understand the model.

Change the upright height from 40 to 50 mm in the first sketch and confirm the holes and fillet update without errors. Change it back.

Export the part as STEP, and take a screenshot of the model with the feature tree visible.

## Why it matters

Mechanical engineers design almost everything in 3D, civil and electrical engineers increasingly use 3D models (BIM, equipment layouts, cable trays), and maintenance teams use models to order parts and plan repairs. A 3D model is a single source of truth: drawings, 3D prints, CNC programs and assembly checks all come from it.

## Parametric, feature-based modelling

Most mechanical CAD tools (SolidWorks, Inventor, Fusion, Onshape, FreeCAD Part Design) work the same way:

1. **Sketch** a 2D profile on a plane, fully constrained with dimensions.
2. **Create a feature** from it: **extrude** (FreeCAD calls it **Pad**), **revolve**, **sweep** or **loft** to add material, or **cut** (FreeCAD: **Pocket**) to remove it.
3. **Add more features** on faces of the solid: holes, fillets, chamfers, patterns.
4. The **feature tree** (history) records every step in order. Change a dimension early in the tree and everything after updates. That is what **parametric** means.

**Design intent** is the idea behind it: model the part the way it should change. If the holes must always stay 12 mm from the ends, dimension them from the ends, not from each other.

## Free 3D tools

- **Onshape free plan**: runs in a browser, saves automatically, good tutorials. Documents on the free plan are **public**, so keep private designs out.
- **FreeCAD**: free and open source, installs locally. Use the **Part Design** workbench for feature-based solids.

Official sites: https://www.onshape.com/en/products/free and https://www.freecad.org/. Checked on 2026-10-23.

## Worked example: the angle bracket in 3D

The bracket from lesson 7: an L 50 mm wide, 40 mm tall, 5 mm thick, 30 mm deep, with two Ø6 holes through the base.

**Plan the model:** one L-shaped profile extruded 30 mm, then holes, then fillets. Three or four features.

1. **New part** in millimetres.
2. **Sketch on the front plane.** Draw the L profile with the line tool starting at the origin: 50 along the bottom, up 5, back 45, up 35, back 5, down 40 to close. Add dimensions 50, 40 and 5 (twice) and constrain it fully; the corner sits on the origin.
3. **Extrude (Pad) 30 mm.** Use a **symmetric** extrude (15 mm each side of the sketch plane) if you want the front plane to be a plane of symmetry; it keeps later features centred.
4. **Holes.** Sketch on the top face of the base: two circles Ø6 with centres 12 mm from each end and centred in depth (a symmetric constraint or 15 mm from the edge). Extrude-cut **through all** (FreeCAD: Pocket, type "Through all"), or use the dedicated **Hole** feature, which records the hole as a hole for drawings.
5. **Fillet** the inside corner of the L with R3 to make it stronger and easier to manufacture.
6. **Check:** measure the model with the measure tool, rename features ("L profile", "Base holes", "Inner fillet") and set a material if the tool supports it to see the mass.
7. **Change test:** edit the first sketch and change the height from 40 to 50. The holes and fillet should update without errors. If something breaks, your references or constraints need fixing.

## From model to drawing and file

- Make a 2D drawing from the model (Onshape: Drawing; FreeCAD: TechDraw) with front, top, side and isometric views; the dimensions come from the model.
- Export **STEP** to share with other CAD tools (the universal format for solids) and **STL** or **3MF** for 3D printing.

## Common mistakes

- Under-constrained sketches that shift when you edit later.
- Building everything in one complicated sketch instead of simple features.
- Dimensioning features from each other instead of from the edges or datums that matter.
- Referencing edges that disappear when an earlier feature changes, causing errors downstream.
- Sharing a native file when the other side needs STEP.

## Recap

- Sketch, constrain, then extrude/revolve or cut; add holes and fillets as features.
- The feature tree makes the model parametric: change early dimensions and the rest updates.
- Capture design intent with good references and constraints.
- Export STEP for CAD exchange and STL/3MF for printing.

## Try it

In the **Do** tab, model the bracket in Onshape's free plan or FreeCAD and test a design change.


Model a simple bracket in a free 3D CAD tool by sketching, extruding and adding holes and fillets.

Intro to 3D modelling

Beginner Tutorial 1/5 - Onshape 3D CAD - Creating Sketches and Objects

FreeCAD Sketch to 3D Solid (Pad + Constraints) [FreeCAD Tutorial 2026 - Part 1]

Sketch a part by hand, then draw it in free 2D CAD and model it in a free 3D tool.