# 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. 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`](https://mellowcad.com/docs/commands/trim.md) then turns each boss's circle into an arc. - **Exercise:** Advanced · Mechanical · 2D - **Commands:** [`CIRCLE`](https://mellowcad.com/docs/commands/circle.md), [`LINE`](https://mellowcad.com/docs/commands/line.md), [`TRIM`](https://mellowcad.com/docs/commands/trim.md), [`DIMLINEAR`](https://mellowcad.com/docs/commands/dimlinear.md), [`DIMRADIUS`](https://mellowcad.com/docs/commands/dimradius.md), [`DIMDIAMETER`](https://mellowcad.com/docs/commands/dimdiameter.md) - **In the editor:** [Open it with its drawing](/draw?drawing=link), dimensioned beside where you draw yours ## The drawing 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`](https://mellowcad.com/docs/commands/circle.md), each by its radius: `20` and `10` at `0,0`, `12` and `6` at `90,0`. 1. Draw the bosses ```text Command: CIRCLE Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 0,0 Specify radius of circle or [Diameter]: 20 Command: CIRCLE Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 0,0 Specify radius of circle or [Diameter] <20.00>: 10 Command: CIRCLE Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 90,0 Specify radius of circle or [Diameter] <10.00>: 12 Command: CIRCLE Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 90,0 Specify radius of circle or [Diameter] <12.00>: 6 ``` ### 2. Draw the tangent lines [`LINE`](https://mellowcad.com/docs/commands/line.md), 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 ```text Command: LINE Specify first point: _TAN to Specify next point or [Undo]: _TAN to Specify next point or [Undo]: Command: LINE Specify first point: _TAN to Specify next point or [Undo]: _TAN to Specify next point or [Undo]: ``` ### 3. Trim the arcs [`TRIM`](https://mellowcad.com/docs/commands/trim.md): 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 ```text Command: TRIM Current settings: Projection=UCS, Edge=None, Mode=Quick Select object to trim or shift-select to extend or [cuTting edges/Crossing/mOde/eRase]: Select object to trim or shift-select to extend or [cuTting edges/Crossing/mOde/eRase/Undo]: Select object to trim or shift-select to extend or [cuTting edges/Crossing/mOde/eRase/Undo]: ``` ### 4. Draw the centre lines On Centre lines, the axis through both centres and a line across each boss. 4. Draw the centre lines ```text Command: LINE Specify first point: -26,0 Specify next point or [Undo]: @134,0 Specify next point or [Undo]: Command: LINE Specify first point: 0,-26 Specify next point or [Undo]: @0,52 Specify next point or [Undo]: Command: LINE Specify first point: 90,-18 Specify next point or [Undo]: @0,36 Specify next point or [Undo]: ``` ### 5. Dimension it On Dimensions, the distance between the centres with [`DIMLINEAR`](https://mellowcad.com/docs/commands/dimlinear.md), the bosses' radii with [`DIMRADIUS`](https://mellowcad.com/docs/commands/dimradius.md) and their bores with [`DIMDIAMETER`](https://mellowcad.com/docs/commands/dimdiameter.md). 5. Dimension it ```text Command: DIMLINEAR Specify first extension line origin or