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Technical Drawing & CAD Basics · CAD Hands-On

Your first 2D CAD drawing

Reading1h 14mLesson 2 of 3 in this module

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

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.

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