by Dennis Collin
When producing Isometric Drawings there is usually a need to draw shapes that represent circular holes or filleted corners. I described the process of starting an isometric drawing of a simple bracket item in a previous blog here.
Unfortunately, the regular Fillet command and Circles do not understand the nature of an isometric drawing grid.
Fig 1. If working with an Isometric grid, Circles do not work! (See Fig. 2)
However, this is where the Ellipse command is useful. If working with an Isometric grid, when using the base Ellipse command from the command prompt, an option to draw an Ellipse with the Isocircle function appears on the command line. (See Figure 3.)
Fig 2. Trying to draw or modify a circle in Isometric mode!
Choosing this option will then draw the ellipse as if it were a typical circle but the ellipse will be aligned to the current isoplane and will look correct and orientate to the current grid lines.
Fig 3. Drawing an Ellipse with the Isocircle option orients the geometry to the current isoplane!
For most reliable results use the ‘raw’ Ellipse command from the command prompt, the default command macro on the Ribbon menu, bypasses the isocircle option and creates incorrect geometry.
Fig 4. Work in progress, use construction lines to locate holes and fillets before using Trim command.
For the application of filleted edges and holes, copy the original ellipse using the grid snap and trim the overlapping geometry. For filleted edges I usually draw some construction lines for assistance, position an ellipse isocircle, copy it and trim any surplus elements to get a desired result.
Fig 5. The finished ‘bracket’
If necessary, keep toggling the Isoplane and finish off the drawing as required. Apply hatching if applicable. Once complete the result will look something like Figure 5.
To form ‘tangential edges’ use the nearest snap as an alternative. It is a rare example when this snap is useful and recommended to be used! In this example the Midpoint snap was used to form the silhouetted edge and complete the shape.
Isometric drafting along with many other more advanced AutoCAD concepts are covered on our Bespoke and follow-on AutoCAD courses. For more details on a range of our courses these please visit https://arkance.world/gb-en/training/