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AutoCAD exercise: a link with tangent lines

Draw a link in AutoCAD: two bosses joined by lines tangent to both with the Tangent object snap, the arcs between them trimmed, and its dimensions. Free online.

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Draw this link, in millimetres: two bosses 90 apart, of radius 20 and 12, bored to radius 10 and 6, joined by lines tangent to both, with the arcs between the lines trimmed away. The tangent lines take the Tangent object snap at both ends; TRIM then turns each boss's circle into an arc.

The drawing

A link of two bosses 90 apart, joined by tangent lines, dimensioned.90R20R12Ø20Ø12
A link of two bosses 90 apart, joined by tangent lines, dimensioned.

Step by step

The engine draws each step and writes its history as you would type it: the prompts in AutoCAD 2027's order, with the same option letters. After a command's first point, a typed point is measured from the last one, as dynamic input measures it, and the history writes it with @; # measures from the origin.

1. Draw the bosses

On the Outline layer, four circles with CIRCLE, each by its radius: 20 and 10 at 0,0, 12 and 6 at 90,0.

1. Draw the bosses
  1. Command: CIRCLE
  2. Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 0,0
  3. Specify radius of circle or [Diameter]: 20
  4. Command: CIRCLE
  5. Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 0,0
  6. Specify radius of circle or [Diameter] <20.00>: 10
  7. Command: CIRCLE
  8. Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 90,0
  9. Specify radius of circle or [Diameter] <10.00>: 12
  10. Command: CIRCLE
  11. Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 90,0
  12. Specify radius of circle or [Diameter] <12.00>: 6
1. Draw the bosses

2. Draw the tangent lines

LINE, then type _TAN, the Tangent object snap for one point, and pick the large circle near its top; _TAN again and pick the small one near its top. The line touches both. The same along the bottom.

2. Draw the tangent lines
  1. Command: LINE
  2. Specify first point: _TAN to
  3. Specify next point or [Undo]: _TAN to
  4. Specify next point or [Undo]:
  5. Command: LINE
  6. Specify first point: _TAN to
  7. Specify next point or [Undo]: _TAN to
  8. Specify next point or [Undo]:
2. Draw the tangent lines

3. Trim the arcs

TRIM: pick each boss between the two lines, on the side that faces the other. The inner arcs are gone and each circle is an arc.

3. Trim the arcs
  1. Command: TRIM
  2. Current settings: Projection=UCS, Edge=None, Mode=Quick
  3. Select object to trim or shift-select to extend or [cuTting edges/Crossing/mOde/eRase]:
  4. Select object to trim or shift-select to extend or [cuTting edges/Crossing/mOde/eRase/Undo]:
  5. Select object to trim or shift-select to extend or [cuTting edges/Crossing/mOde/eRase/Undo]:
3. Trim the arcs

4. Draw the centre lines

On Centre lines, the axis through both centres and a line across each boss.

4. Draw the centre lines
  1. Command: LINE
  2. Specify first point: -26,0
  3. Specify next point or [Undo]: @134,0
  4. Specify next point or [Undo]:
  5. Command: LINE
  6. Specify first point: 0,-26
  7. Specify next point or [Undo]: @0,52
  8. Specify next point or [Undo]:
  9. Command: LINE
  10. Specify first point: 90,-18
  11. Specify next point or [Undo]: @0,36
  12. Specify next point or [Undo]:
4. Draw the centre lines

5. Dimension it

On Dimensions, the distance between the centres with DIMLINEAR, the bosses' radii with DIMRADIUS and their bores with DIMDIAMETER.

5. Dimension it90R20R12Ø20Ø12
  1. Command: DIMLINEAR
  2. Specify first extension line origin or <select object>: 0,0
  3. Specify second extension line origin: @90,0
  4. Non-associative dimension created.
  5. Specify dimension line location or [Text/Angle/Horizontal/Vertical/Rotated]:
  6. Dimension text = 90
  7. Command: DIMRADIUS
  8. Select arc or circle:
  9. Dimension text = 20
  10. Specify dimension line location or [Text/Angle]:
  11. Command: DIMRADIUS
  12. Select arc or circle:
  13. Dimension text = 12
  14. Specify dimension line location or [Text/Angle]:
  15. Command: DIMDIAMETER
  16. Select arc or circle:
  17. Dimension text = 20
  18. Specify dimension line location or [Text/Angle]:
  19. Command: DIMDIAMETER
  20. Select arc or circle:
  21. Dimension text = 12
  22. Specify dimension line location or [Text/Angle]:
5. Dimension it

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