Activity 3.

Orthographic Projections
Terms:
• F.V. – Front View
• L.H.S.V. – Left Hand Side View
• T.V. – Top View
Tools:
• 2H pencil for construction and projection lines
• 0.5-0.6 mm technical pen for outlines
• 0.2-0.3 mm technical pen for engineering lettering, dimensions, dimension lines, leader
lines, extension lines, centerlines, and hidden lines
• T-square and set squares for vertical and horizontal projection lines
• 45°x45° set quares for vertical and horizontal projection line intersection
• Ruler / scale / compass / protractor
• Eraser for removal of projection lines for the final output
Quick Setup
• Draw three aligned rectangles for the three main views (Front, Top, Right Side).
• Lightly project guidelines between the views to keep features aligned.
• Check for alignment by drawing a 45° angle line from the F.V’s bottom right corner to
the intersection of the T.V. and L.H.S.V. projection line intersection
Directions:
• To draw F.V. in the direction of X, L.H.S.V. and T.V.
• As the L.H.S.V. is to be drawn, fix the position of xy at centre of page and x1y1 to the left
side as L.H.S.V. will come to the right of F.V.
• Draw the rectangles for the F.V. (170 x 115), project it down to locate T.V. (170 x 55) and
take the projections of F.V. to left to draw L.H.S.V., complete the rectangle of L.H.S.V. by
taking the projections from T.V.
• First we will start with F.V. Draw the rectangle for base plate 1 70 x 15
• Draw vertical centre lines at 20 mm and 75 mm and 40 mm (consecutive distance) from
left.
• Draw hidden lines for 5 mm depth for two Ø30 spot face holes, draw dotted lines for 2
holes of Ø 15 (Inside these holes).
• Draw horizontal centre line at 35 mm from base, in semi-circle.
• Referring third centre line and this horizontal line draw the circle of 10 mm radius and
semicircle of 20 mm radius.
• Draw vertical lines from end of this semi-circle. Till it touches to base.
• Draw another horizontal centre line at 60 mm above previous horizontal centre line.
• With this as centre, draw circles of Ø10 and Ø25.
• Also draw the arc of radius 20 mm, join this to base with inclined line to represent rib.
• Draw two lines at 3 mm to both the sides, vertical centre lines of the circles to represent
the rib.
• From third centre point, draw centre line at 30°. Draw arcs of 50 mm, 73 mm, 57 mm, 80
mm.
• Draw an arc of centre line pattern of 65 mm radius. (Draw centre line for an arc)
• Taking intersection of this as reference and horizontal centre line draw semi-circle of
radius 15 mm and 8 mm.
• Also draw same arcs, where this line intersects with 30° inclined line.
• Erase unwanted arcs if any.
• Draw inclined line at 15° from left end of block. Show the required dimensions. Now
project all the required line to draw T.V.
• Now draw the top view
• Complete the rectangle of the top view (170 x 55)
• Project the centre lines. (Vertical at 20, 75 and 40 consecutive distances from left and
at 20 above base)
• Draw the two circles of Ø30 and Ø15 to represent spot holes.
• Draw projection of inclined rib 10 thick and circular slot 15 thick.
• Draw hidden lines for inner circular slot.
• Draw rectangle for semicircular projection from F.V. projections
• Draw hidden lines for hole of Ø20 in it.
• Show the projections of bosse holes.
• Draw hidden lines for hole of Ø10. Show the required dimensions.
• Take projections from F.V. and T.V. to complete L.H.S.V.
• Complete the base rectangle of 55 mm x 15 mm. To represent the base.
• Complete the rectangle at left side in L shape of 10 mm thick.
• Show the projections of projected semi-circle.
• Show hidden lines of hole in it.
• Show projection of projected slot and show hidden lines in it.
• Draw projection of boss and show hole in it by dotted line.
• Show inclined line for the rib. (h) Draw front view, top view and L.H.S.V. in their relative
position.
• Verify alignment of features between views (holes and slots should line up).
• Erase unnecessary construction lines.
• Review for neatness and clarity — every feature in the isometric should be represented
correctly in at least one orthographic view.
Activity 4. Isometric Projection

Tools:
• 2H pencil for construction lines
• 30°/60° set square (or isometric grid)
• 0.5-0.6 mm technical pen for outlines
• 0.2-0.3 mm technical pen for engineering lettering, dimensions, dimension lines, leader
lines, extension lines, centerlines, and hidden lines
• T-square and set squares for vertical and horizontal projection lines
• Eraser for removal of projection lines for the final output
• Ruler / scale / compass / protractor
• Ellipse template or French curve (recommended)
Quick Setup:
• Use isometric projection with the usual axes: vertical (Z) up, and two axes at 30° left and
30° right from horizontal. Lines parallel to these axes are drawn true length (no
foreshortening).
• Draw light construction lines first. Ink or darken only after checking everything.
• Refer to the drawing’s dimensions while constructing: base thickness 15 mm, slot offset
15 mm, slot width 16 mm, R50 center for arch, upright block length 35 mm, boss Ø20,
top boss Ø25 (5 mm high) with hole Ø10, brace width 6 mm, etc.
Directions:
1. Establish the isometric axes
o Lightly draw a vertical construction line for Z. From a point near the lower-left,
draw two 30° lines (one to the right, one to the left) for the isometric X and Y
axes. Mark these axes lightly.
2. Draw the top face outline of the base (top rectangle in isometric)
o Using the given plan dimensions, lay off the top surface rectangle along the two
30° axes and vertical as needed. Work from a chosen origin point. (For exam
practice, pick the lower-left front corner as origin.)
o Draw the top outline of the base as a parallelogram: length along the right 30°
axis, width along the left 30° axis.
3. Draw the base thickness (drop the verticals)
o From each top corner, drop vertical construction lines downwards equal to the
base thickness (15 mm). Connect the lower ends to form the visible front and side
faces of the base. Darken the visible edges.
4. Mark hole and feature centrelines on the top face (plan projection)
o On the top surface, measure and mark the center positions of the two recessed
holes and the center of the upright block. Project those centerpoints in isometric:
locate them along the corresponding 30° axes distances shown on the drawing
(e.g., 20 mm, 75 mm segments etc.). Use dashed centerlines where needed.
5. Draw the countersunk / counterbore hole(s) as ellipses
o Each circular hole on a plane parallel to the top face will appear as an ellipse in
isometric. To draw an ellipse:
▪ Construct the isometric bounding rhombus (the top view’s square
bounding the circle projected to the isometric plane). Use the circle’s
diameter and draw the rhombus aligned to the 30° axes.
 ▪ Use an ellipse template or freehand the ellipse tangent to the midpoints of
the rhombus sides. For multiple depth features (Ø30 × 5 deep, spotface
Ø15 etc.) draw the outer ellipse for the counterbore and an inner ellipse for
the through hole; add cross centerlines (dashed) inside the ellipses to show
the hole centers.
6. Draw the right-hand upright block (rectangular block on the base)
o From the block centerline on the top face, draw the block footprint in isometric
(rectangle). Project verticals up for the block height. Draw the top face of the
block and the vertical front face. Dimension from drawing: the block length along
the base is 35 mm (use that to set the top rectangle length).
7. Construct the semicircular upright top (front face)
o On the front face of the upright block, draw the semicircular top: find the
centerline vertically on that face and draw an arc of radius R20 (use the front face
as a plane — the semicircle appears true in that plane). In isometric it will look as
a rounded top attached to the rectangular block.
o Place the Ø20 hole at the semicircle center; on the semicircular face the hole will
project as an ellipse — draw the ellipse centered on the centerline and add the
center cross.
8. Draw the triangular spacer/brace with centre hole and dimensions
o From the block top, project the brace upward at the slanted direction shown. Use
the given brace width (6 mm) — draw two parallel slanted longitudinal lines from
the semicircular boss up to the top boss position. Connect and draw the triangular
web shapes. Add the bracing edges that connect to the top boss. Use light dashed
construction lines to locate the top boss center.
9. Draw the top boss and small hole at the arch top
o At the top position (where the arch meets the small boss), draw a circular boss
(Ø25 by 5 mm high). In isometric the boss cylinder’s circular face appears as an
ellipse. Draw the outer ellipse for the boss and a concentric inner ellipse for the
hole Ø10. Add a small vertical rectangle on the boss where it meets the arch to
show the boss height (5 mm). Add center dashed lines.
10. Draw the curved arch main body (outer profile)
o Find the arch center (R50) approximate by projecting from the upright block
centerline in plan: locate the R50 centre point along the isometric axes. From that
center, draw the outer arcs forming the curved arch. Because the arch is in a plane
that is vertical and tilted, you can construct the arc in its plane and project it into
isometric by plotting points on the arc and connecting with smooth curve. Use
several construction points and a French curve for accuracy.
 11. Draw the slot inside the arch (inner profile and round ends)
o The slot is an inner offset of the outer arch. The drawing shows an offset from
outer edge (15 mm) and slot width 16 mm. Method:
o From the outer arch construction, offset the entire curve inward by the given
offset (15 mm) to get the inner wall. This may require transferring normals at
several points — mark key points (top, left, right), offset them, then blend with
arcs of the appropriate radii and circular endcaps.
o The slot ends are semi-circular: draw them using the same centerline of the slot
end arcs. In isometric they appear as rounded elliptical ends; draw them using
your French curve or ellipse template.
12. Add the thin face thickness of the arch (top and side faces)
o The arch has thickness (you can see the top face and the visible outer edge).
Project the thickness as small vertical/axis-parallel edges (use the isometric axes
to offset the inner arc to show the thickness). Connect and darken visible edges.
13. Connect the arch to the base with the ramp/fillet details and the sloped tangent piece
o At the base left the arch meets a tapered sloping piece (15° slope, R15 fillet).
Draw the sloped face by projecting the 15° slope on the correct plane: mark the
sloping edge on the top face and drop the appropriate verticals. Add the small
fillet radii (R15) and chamfers where shown.
14. Draw auxiliary lines for the brace and show the hidden centrelines
o Add the dashed centerlines and projection lines from holes and bosses down to
the base where dimension lines indicate. These help ensure everything lines up.
15. Check and refine arcs / ellipses
o Recheck all ellipses for holes and bosses so they’re symmetrical and centered.
Use an ellipse template for the holes (Ø20, Ø10, Ø25 boss top) and match the
major/minor axes to the isometric axes.
17. Darken the final visible edges and add hatching for cut or spotfaced features (optional)
• Ink or darken the outer visible outlines. Erase construction lines. Add cross-hatching in
sectional or recessed areas if you are producing a technical rendering.
18. Finishing touches: hidden lines, centerlines, and notes
• Show hidden edges with thin dashed lines. Add center cross marks in holes and a few
dashed projection lines to indicate alignments. Write the important feature notes (e.g.,
Ø30 × 5 deep counterbore, 2 holes Ø15 spotface) near the features with leader lines.
Special tips for the tricky parts
• drawing circles as isometric ellipses: draw the circle’s bounding square in isometric (a
rhombus) and then sketch the ellipse tangent to the midpoints of that rhombus. An ellipse
template makes this quick and accurate.
• curved arch offset/slot: don’t try to offset the whole curve by eye—mark several normals
(at top, left, right) and offset those points exactly, then blend through them with a French
curve.
• bosses and small cylinders: draw the top face ellipse first, then drop the correct vertical
height and close the cylinder with a lower ellipse if visible. Keep center crosshairs to
align features with the parts below.
 DRWN11E – Engineering Drawing and Plans
Rubric for Grading
Activity 4. Isometric Projection
Name:
Section:
Semester and AY:

Criteria Description Points Grading

Accuracy of Correctness of angles (30° axes), proportions, and 25
Projection alignment of features compared to the given object.
Completeness of All features of the object are represented (slots, holes, 20
Views bosses, fillets, arcs, hidden parts where needed).
Line Quality & Use of proper line weights: thick for visible edges, 15
Weight dashed for hidden lines, thin for
construction/centerlines. Lines must be clean and sharp.
Geometry & Circles, arcs, ellipses, and slots are drawn properly with 15
Features correct orientation and placement.
Dimensioning & Necessary dimensions, labels, and centerlines are 10
Annotations included neatly and in the correct format.
Neatness & Overall drawing neatness, absence of smudges, legible 10
Presentation lettering, and proper sheet layout.
Compliance with Title block filled, scale followed (1:1), correct 5
Instructions projection method applied.

Checked and validated by:

ENGR. ARJAY M. DULAY

Instructor, DRWN11E