Slide Set 3 – Orthographic Projection II – Isometric .

BNG 101 – Engineering GraphicsSlide Set 3 – Orthographic Projection II –Isometric Projection(Read Planchard 2-1 to 2-10)

Projections

Types of axonometric projectionsDimetricTwo of the three axes have equal angles (usuallyaround 105 )

Types of axonometric projectionsTrimetricThere are no equal angles between the coordinateaxes

Types of axonometric projectionsIsometricAll the angles between the coordinate axes areequal (120 )

Comparing axonometric 009 09 22/axonometric projections.jpg

Isometric projection – a closer lookWhat is the true angle between the axes?Do the sides shown represent the true lengths of the cube sides?

Isometric projection – a closer look10.82What is the true length of the cube sides?

Isometric projection versus drawing

Circles in isometric drawings Circles cannot betransferred directly tothe isometric drawing.As the object is rotatedto view it as isometric,holes and cylindricalfeatures also rotate andappear as ellipsesrather than true circles

Isometric Limitations

Exercise 1Draw the isometric view of a cube with side lengths 25 mm(spacing between lines on your isometric paper is 5 mm).The “front” face is drawn for you below:

Isometric drawing orientationHow do we know which octant the cube goes in?

Exercise 2Draw the isometric view for the following object (spacing is5 mm). Use point “O” for orientation:

Exercise 3Draw the isometric view for the following object (spacing is5 mm). Use point “O” for orientation:(final shape)Let’s see how we got the answer using subtractive steps

Exercise 3 (cont.)

Exercise 3 (cont.)

Exercise 3 (cont.)

Exercise 4Draw the isometric view for the following object (spacing is5 mm). Use point “O” for orientation:

Isometric drawing – inclined surfaces The object representedat right will be drawnas an isometricdrawing using thefollowing steps Note the orientation ofthe inclined surfaceand the measurementsAODCEFBGOO

Isometric drawing – step 1 Step 1 – Sketching theobject as if it were acomplete cube withoutany cuts.– The measurements ofoverall Width (A),Height (B) and Depth(C) are transferred fromthe orthographic to theisometric by countinggrid spacesOStep 1

Isometric drawing – step 2 Step 2 – The angle ofthe inclined surfacecannot be transferreddirectly. Locate thecorners of the inclinedsurface and then drawlines to connect thecorners Notice that edges thatare parallel in theorthographic viewswill also be parallel inthe isometric drawingStep 2

Isometric drawing – step 3 Step 3 – Add therectangular cut acrossthe left top edge.Notice that the rear ofthe edge of the cutdisappears behind theraised portion of theblock.Step 3

Isometric drawing – step 4 Step 4 – Add therectangular cut acrossthe left top edge.Notice that the rear ofthe edge of the cutdisappears behind theraised portion of theblock.Step 4

Exercise 5Draw the isometric view for the following object (gridspacing shown is 5 mm). Use point “O” for orientation:

Exercise 6Draw the isometric view for the following object (gridspacing shown is 5 mm). Use point “O” for orientation:

Isometric drawing – step 1 Step 1 – Sketching the object as if it were a complete cube without any cuts. – The measurements of overall Width (A), Height (B) and Depth (C) are transferred from the orthographic to the isometric by counting grid spaces . O. Step 1