Question 1 of 5: Views, dimensioning, CAD sequence and manufacture of a pipe-saddle clamp

Question 1: Views, dimensioning, CAD sequence and manufacture of a pipe-saddle clamp (50 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Reading the pictorial. The part is a pipe-saddle clamp of constant cross-section and uniform wall thickness. Along its length it has five zones:

• A flat mounting flange at the left, with two vertical bolt holes and rounded outer corners.
• A half-cylindrical arch that rises above the flange. Underneath it is an open semicircular groove running the full width, which seats a pipe or round bar.
• A flat base strip.
• An upright end wall at the right. It is taller than the arch and has two horizontal through-holes and rounded top corners.

The underside is one flat plane, interrupted only by the groove. Small fillets blend the arch into the flange and the base, and the base into the wall. The shipped pictorial is not dimensioned, so the proportions below are read from it (length ≈ 1.6 × width, wall height ≈ 0.6 × width).

a) Third-angle orthographic views

Choice of views. The profile is constant across the width, so the front view should look along the width. That makes the profile (flange, arch, groove, base, wall) appear in true shape as the view’s outline. Two more views are needed:

• The top view shows the flange holes as circles and the rounded flange corners.
• The right-side view shows the wall holes as circles and the rounded wall corners.

In third-angle projection the top view sits directly above the front view and the right-side view directly to its right, joined by projectors (same length in front and top, same height in front and side).

1. Front view: the profile outline. The flange holes appear as a pair of hidden vertical lines through the flange thickness. The wall holes appear as a pair of hidden horizontal lines through the wall. Centre lines mark the hole axes and the arch centre on the base plane.
2. Top view: the rectangular plan with rounded left corners and the two flange holes as visible circles. Thin tangent lines mark where the fillets meet the flat surfaces. A visible line marks the wall’s inner top edge. The groove edges are hidden lines. Each wall hole is a hidden pair of lines through the wall thickness.
3. Right-side view: the wall face with rounded top corners and the two wall holes as visible circles. Hidden lines show, behind the wall, the plate top, the groove crown and the arch crown, plus the two flange holes.

b) Full dimensioning

Approach (ASME Y14.5 / CSA B78.2 practice). Each feature is dimensioned once, in the view where it appears in true shape, and never to a hidden line. Dimensions go outside the views where practical and run from functional datums: the bottom face, the left end and the front face.

• Front view (profile): overall length and overall height; plate thickness and wall thickness; the arch centre located from the left end; arch inner and outer radii as Rxx leaders from the common centre; a general note for the small fillets.
• Top view: overall width. The flange holes are located from the left end and the front face, with the centre-to-centre spacing, and called out once as 2X ⌀xx THRU. The corner rounds are called out as 2X Rxx.
• Right-side view: the wall holes are located by height above the base and by edge distance plus spacing, and called out as 2X ⌀xx THRU. The wall top rounds are called out as 2X Rxx.

No dimension is repeated between views.

c) Feature-based solid-modelling sequence

The design intent is a constant section of uniform thickness, so the model should be built from one profile sketch. This is more robust than adding and cutting blocks, because every later change (thickness, arch radius) then happens in a single sketch.

1. Base feature: extruded profile. Sketch the complete closed profile on the FRONT plane: flange line, two concentric arcs for the arch and the groove, base line, wall. Fully constrain it: arcs concentric with their centre on the bottom line, horizontal and vertical relations, and thickness dimensions equal. Then extrude it mid-plane by the width W.
2. Flange holes. On the flange top face, sketch two circles, dimensioned from the left end and the mid-plane. Use an extruded cut Through All, or the Hole Wizard. A mirror about the mid-plane keeps the holes symmetric.
3. Wall holes. On the wall’s outer face, sketch two circles at the hole height and cut Up To Next (through the wall only).
4. Rounds and fillets last. Add rounds to the two vertical flange-end edges and the two wall-top edges. Add fillets at the arch roots and the base-to-wall corner, unless they were already drawn in the step-1 sketch. Filleting last avoids references to edges that a later feature would consume.

d) Manufacturing methods and issues

The constant section with uniform thickness is the key to choosing a process. It points to extrusion or forming rather than removing material from solid.

• Aluminium extrusion, then machining (best for medium to high volume). Extrude the full profile, including the groove, arch and fillets, as a long bar (6061-T6 or 6063). Saw it to length W, then CNC-drill the four holes and mill the corner rounds. Die cost is modest, the profile needs no draft, and material waste is small.
  • The corner rounds and all four holes run across the extrusion direction, so they are always secondary operations.
  • The flange holes (vertical) and wall holes (horizontal) are perpendicular to each other. That needs two set-ups or a right-angle fixture, which can shift the two hole patterns relative to each other.
  • Saw cuts leave burrs. Extrusion tolerances on the profile are wider than machined tolerances.
• Press-formed steel plate (high volume, lowest piece cost). Blank and punch the holes flat, then form the arch and bend up the wall on a press brake or a progressive die. This shape can in principle be formed because the thickness is uniform.
  • Every bend gets an inside and outside radius, so the sharp outer corner at the wall root in the pictorial would become a radius.
  • The 180° arch springs back, so the groove diameter needs over-forming or a restrike.
  • Holes too close to a bend distort. Keep them at least about 2–3 plate thicknesses from any bend.
  • The flat underside must stay coplanar after forming.
• Sand or investment casting, then machining. Workable, but it needs draft on the groove and wall faces and machining allowance on the seating surfaces. Porosity is a risk in thin sections. It is overkill for a simple prismatic shape.
• Machining from solid plate or bar (prototypes and one-offs). Simple tooling, but most of the stock is removed (the groove, the space between arch and wall, the whole top), so cycle time and scrap are high. A ball or radius cutter is needed for the arch.

General issues:

• If the groove seats a pipe or shaft, its radius and surface finish are functional, so specify them.
• The two hole patterns must be positioned relative to each other, and to the groove axis.
• Deburr the holes and edges.
• Add a finish for corrosion protection (anodize for aluminium; paint or galvanize for steel).