Tutorial AG: Impeller Lower Casing

Source	Ming C. Leu, Wenjin Tao, Amir Ghazanfari and Krishna Kolan, NX 12 for Engineering Design (Missouri University of Science and Technology), section 3.5.2. The book’s chapter 4.4 then revolves this sketch into the casing: tutorial AO.
You learn	Profile with tangent arcs, a fixed point to dimension from, radius dimensions, Move Curve with Copy Original, joining curve ends with lines
Sizes	the book’s, in inches, typed in millimetres. Line 1 is 15 below the origin and 7.3 long. Curve 1 has a radius of 33 and Curve 2 of 8. Line 2 is 8.1 below the origin and 1.0 long. The copies are 0.5 up (the wall), 1.5 down (the edge), and the flange is 0.5 wide.

Step by step

1. A new part and a sketch

Ctrl+N. The book makes an inch part. NX-Style parts are metric, so the sizes are typed in millimetres (15 in = 381 mm). Click Sketch, pick the XC-YC plane and press MB2.

2. The inner curve

Press Z for Profile. Draw Line 1 below the origin, from left to right. Press M three times for a tangent arc and click Curve 1’s end. Press M three times again for the second tangent arc, Curve 2, which bends the other way. After an arc, FreeCAD starts with a tangent line, so it takes three presses again. Press M twice for a plain line (NX’s Line; FreeCAD would hold it tangent to the arc), click Line 2’s end and press MB2. Line 1 and Line 2 get Horizontal as they are drawn. Then click Tangent where it is missing, between Curve 2 and Line 2; the other joints are tangent already.

3. A point at the origin, and the dimensions

Click Point and click the origin. The point snaps to it, which fixes it there. In NX you type the point’s coordinates and click Fixed. FreeCAD’s Fixed keeps a point where it already is.

Dimension from the point: Line 1 15 below it and Line 2 8.1 below it (Distance), Curve 1 radius 33 and Curve 2 radius 8 (Radius / Diameter), Line 1 7.3 long and Line 2 1.0 long. One degree of freedom is left: nothing places the curve along X. The book leaves it too, because the casing is later revolved about the X axis.

Select the dimensions, then MB3 > Hide (or Ctrl+B).

The curve after Hide: the dimensions are gone

4. Move Curve: the wall, the edge and the flange

Select the four curves and click Move Curve. Set Copies to 1 so that the curves are copied, not moved (NX: Copy Original). Click a base point, then type the move in the fields beside the pointer: length 12.7 mm, angle 90°. Join the two ends with lines (L). That closes the casing wall.

Copy the four curves again, 38.1 mm at -90° (1.5 in down), and join their ends to the inner curve. That is the edge, which the next chapter extrudes.

At the small end, copy the edge’s end line 12.7 mm at 180° (0.5 in along -XC), and join the two lines at the top and the bottom. That is the flange. The sketch now has 19 curves.

Ctrl+Q, and save with Ctrl+S.

The replay

#	In the book (NX)	In FreeCAD NX-Style	Result	Notes
AG1	Create a new file in inches (Impeller_lower_casing)	Ctrl+N, Model template	same	new document ['Unnamed']
AG2	Units in the New dialog (the book picks inches)	metric part kept; book sizes typed in mm	differs	FreeCAD sets units in Preferences, not in the New dialog; NXStyle defaults to millimetres (document: Standard (mm, kg, s, °); 25.4 mm shows as 25.40 mm)
AG3	Sketch in Task Environment on the XC-YC plane	ribbon 'Home › Direct Sketch > Sketch', plane row + MB2	same	picked XY-plane (Base plane); FreeCAD edits every sketch in its own environment, as NX’s task environment
AG4	Profile: Line 1, Curve 1, Curve 2, Line 2	Z key, 5 MB1 clicks, M (3x) before Curve 1’s end, 3x before Curve 2’s and 2x before Line 2’s (NX’s Line), MB2	same	curves ['line', 'arc', 'arc', 'line']; tangent joints 2 (Line 1-Curve 1, Curve 1-Curve 2; Line 2 is drawn as a plain line); Horizontal on Line 1 True, on Line 2 True; tool ended by MB2 True; DoF 8
AG5	A point at the origin (0, 0, 0), then Fixed	ribbon 'Sketch › Curve > Point', MB1 at the origin	differs	point at (0.0000, 0.0000) mm; the click snapped to the origin; DoF 8. FreeCAD’s Fixed keeps a point where it is, so Coincident with the origin puts it at (0, 0, 0), as NX’s typed coordinates do
AG6	Tangent at every curve-line and curve-curve joint	ribbon 'Tangent' where missing	same	made by Profile; added ['3-4 (0)']
AG7	Dimensions: p1 15, p2 7.3, R 33, R 8, p6 8.1, p4 1.0	picks + ribbon 'Sketch › Constraints > Distance' and 'Radius / Diameter', each value typed in FreeCAD’s dimension dialog (biggest first)	same	Curve 1 radius 33, Line 1 15 below the origin, Line 2 8.1 below the origin, Curve 2 radius 8, Line 1 7.3 long, Line 2 1.0 long; DoF 1 ('Under-constrained: / 1 Degrees of Freedom'): only the position along X is left free, as in the book; the four curves match the book’s figure
AG8	Select all the dimensions, MB3 > Hide	dimensions selected, MB3 on empty space > Hide	same	6 of 6 dimensions hidden (FreeCAD’s 'virtual space'); the sketch’s own visibility untouched True; menu ['Toggle Driving/Reference Constraints', 'Toggle Constraints', 'Select Associated Geometry', 'Hide', 'Delete']
AG9	Move Curve: the 4 curves, Distance 0.5 along YC, Copy Original	4 curves selected + ribbon 'Sketch › Edit Curve > Move Curve', base point, offset typed	same	4 copies made; largest error 5.2e-06 mm
AG10	Join the end points at the two ends: the casing wall is closed	L key, MB1 on each end point, MB2 (2 lines)	same	2 lines; 4 of 4 ends snapped to the curves
AG11	Move Curve: the lower curve, -1.5 along YC, Copy Original	4 curves selected + ribbon 'Sketch › Edit Curve > Move Curve', base point, offset typed	same	4 copies made; largest error 6.6e-05 mm
AG12	Straight lines join it with the inside curve: a closed chain	L key, MB1 on each end point, MB2 (2 lines)	same	2 lines; 4 of 4 ends snapped to the curves
AG13	Move Curve: the outer end line, -0.5 along XC, Copy Original	1 curves selected + ribbon 'Sketch › Edit Curve > Move Curve', base point, offset typed	same	1 copies made; largest error 5.6e-07 mm
AG14	Straight lines join the two lines: the flange’s rectangle	L key, MB1 on each end point, MB2 (2 lines)	same	2 lines; 4 of 4 ends snapped to the curves
AG15	The sketch: 19 curves (the casing wall, its edge, the flange)	compared with the book’s figure	same	19 curves; all 19 match the book; DoF 8 ('Under-constrained: / 8 Degrees of Freedom'): the copies keep no constraints, like NX’s non-associative copies. The next chapter revolves the wall and the flange about the X axis and extrudes the edge
AG16	Finish Sketch	Ctrl+Q	same	sketch edit ended True; the sketch is shown True (its dimensions stay hidden)
AG17	Save and close the file	file name given once by script (the system file dialog is not driven); a change, then the Ctrl+S key	same	Impeller_lower_casing.FCStd rewritten by Ctrl+S: the file holds the change and the part is unmodified afterwards (modified before the key: True); FreeCAD format, not .prt

In the book (NX)

In FreeCAD NX-Style

Result

Notes

AG1

Create a new file in inches (Impeller_lower_casing)

Ctrl+N, Model template

same

new document ['Unnamed']

AG2

Units in the New dialog (the book picks inches)

metric part kept; book sizes typed in mm

differs

FreeCAD sets units in Preferences, not in the New dialog; NXStyle defaults to millimetres (document: Standard (mm, kg, s, °); 25.4 mm shows as 25.40 mm)

AG3

Sketch in Task Environment on the XC-YC plane

ribbon 'Home › Direct Sketch > Sketch', plane row + MB2

same

picked XY-plane (Base plane); FreeCAD edits every sketch in its own environment, as NX’s task environment

AG4

Profile: Line 1, Curve 1, Curve 2, Line 2

Z key, 5 MB1 clicks, M (3x) before Curve 1’s end, 3x before Curve 2’s and 2x before Line 2’s (NX’s Line), MB2

same

curves ['line', 'arc', 'arc', 'line']; tangent joints 2 (Line 1-Curve 1, Curve 1-Curve 2; Line 2 is drawn as a plain line); Horizontal on Line 1 True, on Line 2 True; tool ended by MB2 True; DoF 8

AG5

A point at the origin (0, 0, 0), then Fixed

ribbon 'Sketch › Curve > Point', MB1 at the origin

differs

point at (0.0000, 0.0000) mm; the click snapped to the origin; DoF 8. FreeCAD’s Fixed keeps a point where it is, so Coincident with the origin puts it at (0, 0, 0), as NX’s typed coordinates do

AG6

Tangent at every curve-line and curve-curve joint

ribbon 'Tangent' where missing

same

made by Profile; added ['3-4 (0)']

AG7

Dimensions: p1 15, p2 7.3, R 33, R 8, p6 8.1, p4 1.0

picks + ribbon 'Sketch › Constraints > Distance' and 'Radius / Diameter', each value typed in FreeCAD’s dimension dialog (biggest first)

same

Curve 1 radius 33, Line 1 15 below the origin, Line 2 8.1 below the origin, Curve 2 radius 8, Line 1 7.3 long, Line 2 1.0 long; DoF 1 ('Under-constrained: / 1 Degrees of Freedom'): only the position along X is left free, as in the book; the four curves match the book’s figure

AG8

Select all the dimensions, MB3 > Hide

dimensions selected, MB3 on empty space > Hide

same

6 of 6 dimensions hidden (FreeCAD’s 'virtual space'); the sketch’s own visibility untouched True; menu ['Toggle Driving/Reference Constraints', 'Toggle Constraints', 'Select Associated Geometry', 'Hide', 'Delete']

AG9

Move Curve: the 4 curves, Distance 0.5 along YC, Copy Original

4 curves selected + ribbon 'Sketch › Edit Curve > Move Curve', base point, offset typed

same

4 copies made; largest error 5.2e-06 mm

AG10

Join the end points at the two ends: the casing wall is closed

L key, MB1 on each end point, MB2 (2 lines)

same

2 lines; 4 of 4 ends snapped to the curves

AG11

Move Curve: the lower curve, -1.5 along YC, Copy Original

4 curves selected + ribbon 'Sketch › Edit Curve > Move Curve', base point, offset typed

same

4 copies made; largest error 6.6e-05 mm

AG12

Straight lines join it with the inside curve: a closed chain

L key, MB1 on each end point, MB2 (2 lines)

same

2 lines; 4 of 4 ends snapped to the curves

AG13

Move Curve: the outer end line, -0.5 along XC, Copy Original

1 curves selected + ribbon 'Sketch › Edit Curve > Move Curve', base point, offset typed

same

1 copies made; largest error 5.6e-07 mm

AG14

Straight lines join the two lines: the flange’s rectangle

L key, MB1 on each end point, MB2 (2 lines)

same

2 lines; 4 of 4 ends snapped to the curves

AG15

The sketch: 19 curves (the casing wall, its edge, the flange)

compared with the book’s figure

same

19 curves; all 19 match the book; DoF 8 ('Under-constrained: / 8 Degrees of Freedom'): the copies keep no constraints, like NX’s non-associative copies. The next chapter revolves the wall and the flange about the X axis and extrudes the edge

AG16

Finish Sketch

Ctrl+Q

same

sketch edit ended True; the sketch is shown True (its dimensions stay hidden)

AG17

Save and close the file

file name given once by script (the system file dialog is not driven); a change, then the Ctrl+S key

same

Impeller_lower_casing.FCStd rewritten by Ctrl+S: the file holds the change and the part is unmodified afterwards (modified before the key: True); FreeCAD format, not .prt

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.

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.

Each of the 19 curves is compared with the book’s figure, rebuilt from its dimensions.

What differs from NX

FreeCAD gives Move Curve’s distance as a length and an angle. NX takes a distance along a chosen vector.
Copies = 1 is NX’s Copy Original. With 0, FreeCAD moves the curves.
Hidden sketch dimensions go to FreeCAD’s "virtual space". Its constraint list still shows them; Show All (Ctrl+Shift+U) brings them back.