Tutorial K: Parameter-driven flat bar

Book

Leake and Borgerson, Engineering Design Graphics, ch. 7, Fig. 7-30
You learn

The Expressions table (Ctrl+E), dimensions tied to names, configurations
Sizes

L, N and D for two configurations (A: 1219.2 mm, 5 holes, 50.8 mm; B: 914.4 mm, 8 holes, 25.4 mm; the book’s 48, 5, 2 and 36, 8, 1 in). Width, thickness and hole size are not given: 50.8 × 12.7 mm and Ø12.7 here.
The flat bar in configuration B

In short

  1. Ctrl+E: type L, N_holes, D and hole_spacing = (L - 2*D) / (N_holes - 1) into the Expressions sheet.

  2. Sketch the bar; its length is =Expressions.L.

  3. The first hole at D from the end; Pattern Feature with N_holes occurrences, hole_spacing apart.

  4. Type configuration B’s values into the same sheet: the bar follows.

Step by step

# In the book (NX) In FreeCAD NX-Style Result Notes

K1

Tools > Expressions (Ctrl+E): L = 48, N = 5, D = 2 (in)

Ctrl+E opens NXStyle’s Expressions sheet; names and values typed into its cells

differs

cells {'A2': "'L", 'B2': '=1219.2 mm', 'A3': "'N", 'B3': '5', 'A4': "'D", 'B4': '=50.8 mm'}; NX lists expressions in a dialog, FreeCAD keeps them in a spreadsheet

K2

Names L, N, D and the equation hole_spacing = (L - 2D)/(N - 1)

alias per value cell (cell properties); equation typed into B5

differs

hole_spacing = 279.400 mm (279.400 expected, the book’s 11 in); names refused: N (Invalid alias: a unit symbol, newton); used {'L': 'L', 'N': 'N_holes', 'D': 'D'}

K3

Create the flat bar: Extrude (X), XY plane

X key, plane row + MB2

same

picked XY-plane (Base plane)

K4

Rectangle, its length = L

R key + 2 MB1 clicks + MB2; length tied to the expression

differs

DoF 0; NX types 'L' in the dimension, FreeCAD types '=Expressions.L' (f(x)) in it

K5

Extrude the bar, 0.5 in thick

Ctrl+Q, 'lengthEdit' = 12.7 mm, MB2 = OK

same

volume 786579.1 mm^3, expected 786579.1; 1 solid(s)

K6

Create a hole at one end of the bar

top face + ribbon 'Home › Feature > Hole'

differs

FreeCAD’s Hole drills at circle centres in a sketch on the face

K7

Hole centre at D from the end, on the centre line

O key + 2 MB1 clicks + MB2; distance from the projected end tied to D

same

DoF 0; 50.800 mm from the end, 25.400 mm from the edge

K8

Hole Ø0.5 through

'Diameter' = 12.7 mm, 'Through all', MB2 = OK

same

volume 784970.3 mm^3, expected 784970.3; 1 solid(s)

K9

Rectangular array of the hole: count N, spacing hole_spacing

hole + ribbon 'Home › Pattern > Pattern Feature', X axis, {'axis': 'Base X-axis', 'mode': 'Spacing', 'count typed': 5, 'spacing': 11.0}; count and spacing tied to N and hole_spacing (f(x))

differs

length 1219.200 mm, 5 holes, first at 50.800 mm, last 1168.400 mm, pitch 279.4000 mm (279.4000 wanted); volume 778535 mm^3 (778535 wanted); NX: the array’s count and pitch fields take the expression names directly

K10

Configuration B: L 36, N 8, D 1

values typed into the sheet’s cells

same

length 914.400 mm, 8 holes, first at 25.400 mm, last 889.000 mm, pitch 123.3714 mm (123.3714 wanted); volume 577064 mm^3 (577064 wanted)

K11

The part is shown in the graphics window

render of the graphics window

same

2.9% of the view shows the part
Result Means

same

The book’s NX steps work as written.

differs

It works, but the FreeCAD way is different; the notes say how.

limit

The book’s way fails in FreeCAD itself; a workaround follows in the next steps.

missing

FreeCAD has no such function; a stand-in follows.

skipped

Not replayed; the notes give the reason.

FAILED

Did not work.

What differs from NX

  • NX lists expressions in a dialog; FreeCAD keeps them in a spreadsheet. A dimension refers to a cell as =Expressions.L.

  • FreeCAD refuses names that are unit symbols: the book’s N (the newton) becomes N_holes.