Tutorial AH: Impeller

Source	Ming C. Leu, Wenjin Tao, Amir Ghazanfari and Krishna Kolan, NX 12 for Engineering Design (Missouri University of Science and Technology), section 3.5.3. The book’s chapter 4.7.5 models the impeller from this sketch: tutorial AU.
You learn	points at given coordinates, Arc by Center and Endpoints, Arc by 3 Points, tangent arcs, radius dimensions
Sizes	the book’s, in inches, typed in millimetres. The points are at the origin and at (11.75, 6). The end arcs have radii of 1.5 and 0.5; the arcs between them 18 (top) and 15 (bottom).

Step by step

1. A new part, a sketch and two points

Ctrl+N, then Sketch on the XC-YC plane and MB2. Click Point and click the origin: the point snaps to it. Type the second point’s coordinates in the XC and YC fields beside the pointer, Enter after each: (11.75, 6) in, which is 298.45 and 152.4 mm. FreeCAD keeps the first point Coincident with the origin and the second at its horizontal and vertical distances from the axes.

2. The two end arcs

Press A for Arc (by centre and end points). Click the point at the origin as the centre, then click the arc’s start above it and go round the left side to its end below. Do the same about the second point, round its right side.

3. The two arcs between them

Arc by 3 Points: click the top ends of the two end arcs, then a point between them. Do the same for the bottom ends. In NX-Style, open the Arc drop-down on the Sketch tab and pick Arc From 3 Points (or press A, then M to switch FreeCAD’s Arc to end points and rim point).

4. Tangent, Fixed and the radii

Make each arc Tangent to the next at its end points: four joints. The point at the origin is already fixed, because it is Coincident with the origin. Give the radii, biggest first: 18 and 15 between the ends, 1.5 and 0.5 at the ends.

The impeller blade sketch with its four tangent arcs

Ctrl+Q, and save with Ctrl+S.

The replay

#	In the book (NX)	In FreeCAD NX-Style	Result	Notes
AH1	Create a new file in inches (Impeller_impeller)	Ctrl+N, Model template	same	new document ['Unnamed']
AH2	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)
AH3	Sketch on the XC-YC plane, OK	ribbon 'Home › Direct Sketch > Sketch', plane row + MB2	same	picked XY-plane (Base plane)
AH4	Point: one at (0, 0, 0), one at (11.75, 6, 0)	ribbon 'Sketch › Curve > Point', MB1 on the origin, then XC and YC typed in the on-view fields	same	2 points, at (0.0000, 0.0000) and (11.7500, 6.0000) in; FreeCAD keeps typed coordinates as constraints: [['Coincident'], ['DistanceX', 'DistanceY']]; redundant []
AH5	Arc by Center and Endpoints: R1.5 about the origin point, R0.5 about the other point	A key, MB1 on the centre point, the start, round to the end, MB2 (twice)	same	arcs made; centres on the points True; radii 1.482, 0.526 in (sized below)
AH6	Arc by 3 Points: the top end points, then a point between; the same for the bottom	ribbon 'Sketch > Arc' dropdown > 'Arc From 3 Points', MB1 on both end points and between, MB2 (twice)	same	arcs made [True, True]; 4 of 4 ends snapped to the end arcs
AH7	Constraints: every arc Tangent to the next at its end points	two arcs + ribbon 'Tangent', 4 times	same	4 of 4 joints tangent (0 added); DoF 4
AH8	The point at the origin: Fixed	no click needed: the point is Coincident with the origin	differs	FreeCAD’s Coincident with the origin already fixes it; Fixed on top would be redundant
AH9	Rapid Dimension: the radii 1.5 and 0.5 at the ends, 18 and 15 between	arc + ribbon 'Radius / Diameter', the value typed in FreeCAD’s dialog, 4 times	same	R18, R15, R1.5, R0.5; DoF 0 ('Fully constrained'); every arc within 1.9e-13 mm of the solved figure (centres, radii, ends)
AH10	Finish Sketch	Ctrl+Q	same	sketch edit ended True
AH11	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_impeller.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

AH1

Create a new file in inches (Impeller_impeller)

Ctrl+N, Model template

same

new document ['Unnamed']

AH2

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)

AH3

Sketch on the XC-YC plane, OK

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

same

picked XY-plane (Base plane)

AH4

Point: one at (0, 0, 0), one at (11.75, 6, 0)

ribbon 'Sketch › Curve > Point', MB1 on the origin, then XC and YC typed in the on-view fields

same

2 points, at (0.0000, 0.0000) and (11.7500, 6.0000) in; FreeCAD keeps typed coordinates as constraints: [['Coincident'], ['DistanceX', 'DistanceY']]; redundant []

AH5

Arc by Center and Endpoints: R1.5 about the origin point, R0.5 about the other point

A key, MB1 on the centre point, the start, round to the end, MB2 (twice)

same

arcs made; centres on the points True; radii 1.482, 0.526 in (sized below)

AH6

Arc by 3 Points: the top end points, then a point between; the same for the bottom

ribbon 'Sketch > Arc' dropdown > 'Arc From 3 Points', MB1 on both end points and between, MB2 (twice)

same

arcs made [True, True]; 4 of 4 ends snapped to the end arcs

AH7

Constraints: every arc Tangent to the next at its end points

two arcs + ribbon 'Tangent', 4 times

same

4 of 4 joints tangent (0 added); DoF 4

AH8

The point at the origin: Fixed

no click needed: the point is Coincident with the origin

differs

FreeCAD’s Coincident with the origin already fixes it; Fixed on top would be redundant

AH9

Rapid Dimension: the radii 1.5 and 0.5 at the ends, 18 and 15 between

arc + ribbon 'Radius / Diameter', the value typed in FreeCAD’s dialog, 4 times

same

R18, R15, R1.5, R0.5; DoF 0 ('Fully constrained'); every arc within 1.9e-13 mm of the solved figure (centres, radii, ends)

AH10

Finish Sketch

Ctrl+Q

same

sketch edit ended True

AH11

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_impeller.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.

The four arcs are checked against the figure solved from the book’s data. The R18 arc runs outside both end arcs, so its centre is 18 + 1.5 from the origin and 18 + 0.5 from the second point. The R15 arc holds them inside, at 15 - 1.5 and 15 - 0.5.

What differs from NX

FreeCAD keeps typed coordinates as constraints (distances from the axes), so the second point is held before any dimension is added.
The first point is clicked on the origin, not typed: FreeCAD 1.1.4 gives a point typed at (0, 0) two Coincident constraints with the origin, and the solver flags the second as redundant.
FreeCAD’s Fixed keeps a point where it is. The point clicked on the origin is Coincident with it, which already fixes it.