Tutorial T: A guide bush documented to ISO GPS

Book	The PMI workflow of Wünsch, Pilz and Vajna, Siemens NX für Einsteiger – kurz und bündig, 4th ed., section 6.10 (PMI tab, Rapid Dimension on a cylindrical face, tolerances, the PMI folder); the part is ours
Standards	ISO 16792 (3D annotation), ISO 286 (fits), ISO 14405 (the envelope), ISO 8015 (independency), ISO 2768 (general tolerances), ISO 1101 and ISO 5459 (geometrical tolerances and datums)
You learn	PMI › Tolerancing, Rapid Dimension with a tolerance class, the envelope, datums, frames, Inspection Plan, the ISO 8015 trap, a fit as a stack-up, STEP with PMI, Inherit PMI
Sizes	A flange Ø40 × 8, a body Ø25 × 30 pressed into a housing, a bore Ø16 for a sliding shaft

The bush’s body is pressed into a housing (Ø25 k6 in an H7 hole); its shoulder seats on the housing; a Ø16 g6 shaft slides in its bore.

Step by step

1. The part and its standard

The bush is modelled by script; the exercise is the documentation. PMI › Tolerancing: ISO GPS, general tolerances ISO 2768-mK.

2. Sizes with their fits

Select the body’s cylinder, PMI › Rapid Dimension: tolerance class k6, Envelope ticked, OK: Ø25.000 k6 (+0.015/+0.002) Ⓔ. Then the bore: H7, without the envelope for now.

3. Datums and geometrical tolerances

Datum Feature Symbol A on the body’s cylinder, B on the shoulder. Feature Control Frame: coaxiality Ø0.02 to A on the bore; perpendicularity 0.02 to A on the shoulder.

4. Dimensions without a tolerance of their own

Rapid Dimension between the shoulder and the top: 30, nothing typed; the flange 8 ±0.05. The 30 is covered by ISO 2768-m: ±0.2 (over 6 up to and including 30).

The bush with its PMI: fits with the envelope

5. The inspection plan, and the ISO 8015 trap

PMI › Inspection Plan numbers the six characteristics and checks the PMI. It flags the bore: H7 is a fit, but under ISO 8015 independency the size controls only two-point sizes, not form. A bore within H7 at every section can still be bent or barrel-shaped enough to bind the shaft. Tick the bore’s Envelope in the property view and run the plan again: no warnings.

The inspection plan: characteristics with their limits

6. The fit as a stack-up

Tolerance Stackup, select the bore’s PMI dimension, Add from PMI; Add Typed for the shaft: 16, direction −, class g6. The worst case is a clearance of 0.006 to 0.035 mm, as ISO 286 gives for Ø16 H7/g6. The stack-up reads the bore’s class from the PMI: change it, and the fit follows (tutorial V does).

7. STEP with PMI

PMI › STEP with PMI, a file name, OK. The file holds the bush and its PMI as STEP AP242 data: datums A and B, the two diameters with H7 and k6, the 8 ±0.05 as a size, the 30 as a location, the coaxiality and perpendicularity frames with their datums. OpenCASCADE reads it back: 2 datum references, 4 dimensions, 2 geometrical tolerances. The envelopes and the ISO 2768 note are listed as not written: AP242 in OpenCASCADE has no place for them.

The Information window after STEP with PMI: what the file holds

8. The drawing inherits the PMI

Ctrl+Shift+D, New Sheet, a top view and a front view at 2:1. Select each view and click Inherit PMI: the diameters with k6 and H7 and Ⓔ, the 30 and the 8 ±0.05, the frames, the datum symbols, and the note Tolerancing ISO 8015 · General tolerances ISO 2768-mK.

The replay

#	In the book (NX)	In FreeCAD NX-Style	Result	Notes
T1	The guide bush: flange Ø40 x 8, body Ø25 x 30, bore Ø16	modelled by script (the exercise is the documentation)	same	volume 17139.0 mm^3, expected 17139.0
T2	PMI tab > Tolerancing: ISO GPS, general tolerances ISO 2768-mK	ribbon 'PMI › Standard > Tolerancing', 'ISO 2768-mK' typed, MB2 = OK	differs	standard ISO, general ISO 2768-mK: what a drawing’s title block says (NX keeps it in the drafting standard and a general note); stored with the PMI folder of the part
T3	Rapid Dimension on the body’s cylinder: Ø25 k6 with the envelope Ⓔ (it is pressed into the housing)	body selected + ribbon 'PMI › Dimension > Rapid Dimension'; 'k6' typed, Envelope ticked; MB2 = OK	differs	Ø25.000 k6 (+0.015/+0.002) Ⓔ; NX: the cylindrical face is picked in the graphics window and the PMI placed with a click; here it is placed beside the face
T4	Datum Feature Symbol A on the Ø25 body (its axis)	body selected + ribbon 'PMI › Annotation > Datum Feature Symbol'; letter A; MB2 = OK	differs	datum feature A
T5	Datum Feature Symbol B on the shoulder that seats on the housing	shoulder selected + ribbon 'PMI › Annotation > Datum Feature Symbol'; letter B; MB2 = OK	differs	datum feature B
T6	Rapid Dimension on the bore: Ø16 H7 (no envelope yet)	bore selected + ribbon 'PMI › Dimension > Rapid Dimension'; 'H7' typed; MB2 = OK	differs	Ø16.000 H7 (+0.018/0)
T7	Coaxiality of the bore Ø0.02 to A (ISO 1101; the symbol ASME calls concentricity)	bore selected + ribbon 'PMI › Annotation > Feature Control Frame'; concentricity, Ø0.02, datum A; MB2 = OK	differs	concentricity \| Ø0.020 \| A
T8	Perpendicularity of the shoulder 0.02 to A	shoulder selected + ribbon 'PMI › Annotation > Feature Control Frame'; perpendicularity, 0.02, datum A; MB2 = OK	differs	perpendicularity \| 0.020 \| A
T9	Rapid Dimension: the body’s length 30, no tolerance of its own (ISO 2768-m, over 6 up to 30: ±0.2)	shoulder, top selected + ribbon 'PMI › Dimension > Rapid Dimension'; nothing typed; MB2 = OK	differs	30.000
T10	Rapid Dimension: the flange 8 ±0.05	under, shoulder selected + ribbon 'PMI › Dimension > Rapid Dimension'; +0.05 and −0.05 typed; MB2 = OK	differs	8.000 ±0.050
T11	Inspection Plan: the characteristics, numbered, and the checks	ribbon 'PMI › Inspection > Inspection Plan'	differs	the check finds the bore’s H7 without the envelope: under ISO 8015 a size controls only local two-point sizes, so the fit is not guaranteed. NX has no such check
T12	The bore gets the envelope Ⓔ; the plan again	the PMI’s Envelope property; Inspection Plan	differs	6 characteristics, no errors or warnings; the length 30 inspected at 29.8 to 30.2 (ISO 2768-m); bore Ø16.000 H7 (+0.018/0) Ⓔ
T13	The fit Ø16 H7/g6 as a stack-up: bore from the PMI, shaft by its ISO 286 class	Add from PMI (the bore’s dimension) + Add Typed: 16, '-', class g6	differs	clearance 0.006 to 0.035 mm worst case, as ISO 286 gives for 16 H7/g6 (0.006 to 0.035); a later change of the PMI’s class follows
T14	The bush with its PMI in the graphics window	render of the graphics window	same	5.3% of the view shows the part (an occupancy check: something is drawn; the shape itself is checked by its geometry)
T15	PMI > STEP with PMI: the bush and its PMI as STEP AP242 data	ribbon 'PMI › Exchange > STEP with PMI', the file name typed, MB2 = OK	differs	schema AP242_MANAGED_MODEL_BASED_3D_ENGINEERING_MIM_LF; datums A, B (2 datum systems); sizes: 2 diameter, 1 thickness; locations: 1; with ± tolerances: 3; fits: H7, k6; geometric tolerances: 1 coaxiality, 1 perpendicularity; read back by OpenCASCADE: {'datums': 2, 'dimensions': 4, 'geometric_tolerances': 2}. NX writes PMI to STEP AP242 too; FreeCAD’s own STEP export drops it. The envelope Ⓔ and the ISO 2768 note have no semantic AP242 form in OpenCASCADE and are listed as not written
T16	Drafting: New Sheet, a top view and a front view at 2:1	Ctrl+Shift+D, ribbon 'New Sheet', twice 'Base View' with the body selected	differs	the second Base View stands in for a projected view, as in tutorial H
T17	Inherit PMI on each view: the dimensions with their ISO classes and the envelope, the frames, the datum symbols, and the tolerancing note	each view selected + ribbon 'Drafting > Inherit PMI'	differs	4 dimensions [8.0, 16.0, 25.0, 30.0] (⌀%.3w k6 Ⓔ; ⌀%.3w H7 Ⓔ; %.2w; %.2w), 4 symbols, note ['Tolerancing ISO 8015', 'General tolerances ISO 2768-mK']. NX inherits PMI from a model view into a drawing view; FreeCAD has no PMI, NXStyle adds both

In the book (NX)

In FreeCAD NX-Style

Result

Notes

The guide bush: flange Ø40 x 8, body Ø25 x 30, bore Ø16

modelled by script (the exercise is the documentation)

same

volume 17139.0 mm^3, expected 17139.0

PMI tab > Tolerancing: ISO GPS, general tolerances ISO 2768-mK

ribbon 'PMI › Standard > Tolerancing', 'ISO 2768-mK' typed, MB2 = OK

differs

standard ISO, general ISO 2768-mK: what a drawing’s title block says (NX keeps it in the drafting standard and a general note); stored with the PMI folder of the part

Rapid Dimension on the body’s cylinder: Ø25 k6 with the envelope Ⓔ (it is pressed into the housing)

body selected + ribbon 'PMI › Dimension > Rapid Dimension'; 'k6' typed, Envelope ticked; MB2 = OK

differs

Ø25.000 k6 (+0.015/+0.002) Ⓔ; NX: the cylindrical face is picked in the graphics window and the PMI placed with a click; here it is placed beside the face

Datum Feature Symbol A on the Ø25 body (its axis)

body selected + ribbon 'PMI › Annotation > Datum Feature Symbol'; letter A; MB2 = OK

differs

datum feature A

Datum Feature Symbol B on the shoulder that seats on the housing

shoulder selected + ribbon 'PMI › Annotation > Datum Feature Symbol'; letter B; MB2 = OK

differs

datum feature B

Rapid Dimension on the bore: Ø16 H7 (no envelope yet)

bore selected + ribbon 'PMI › Dimension > Rapid Dimension'; 'H7' typed; MB2 = OK

differs

Ø16.000 H7 (+0.018/0)

Coaxiality of the bore Ø0.02 to A (ISO 1101; the symbol ASME calls concentricity)

bore selected + ribbon 'PMI › Annotation > Feature Control Frame'; concentricity, Ø0.02, datum A; MB2 = OK

differs

concentricity | Ø0.020 | A

Perpendicularity of the shoulder 0.02 to A

shoulder selected + ribbon 'PMI › Annotation > Feature Control Frame'; perpendicularity, 0.02, datum A; MB2 = OK

differs

perpendicularity | 0.020 | A

Rapid Dimension: the body’s length 30, no tolerance of its own (ISO 2768-m, over 6 up to 30: ±0.2)

shoulder, top selected + ribbon 'PMI › Dimension > Rapid Dimension'; nothing typed; MB2 = OK

differs

30.000

T10

Rapid Dimension: the flange 8 ±0.05

under, shoulder selected + ribbon 'PMI › Dimension > Rapid Dimension'; +0.05 and −0.05 typed; MB2 = OK

differs

8.000 ±0.050

T11

Inspection Plan: the characteristics, numbered, and the checks

ribbon 'PMI › Inspection > Inspection Plan'

differs

the check finds the bore’s H7 without the envelope: under ISO 8015 a size controls only local two-point sizes, so the fit is not guaranteed. NX has no such check

T12

The bore gets the envelope Ⓔ; the plan again

the PMI’s Envelope property; Inspection Plan

differs

6 characteristics, no errors or warnings; the length 30 inspected at 29.8 to 30.2 (ISO 2768-m); bore Ø16.000 H7 (+0.018/0) Ⓔ

T13

The fit Ø16 H7/g6 as a stack-up: bore from the PMI, shaft by its ISO 286 class

Add from PMI (the bore’s dimension) + Add Typed: 16, '-', class g6

differs

clearance 0.006 to 0.035 mm worst case, as ISO 286 gives for 16 H7/g6 (0.006 to 0.035); a later change of the PMI’s class follows

T14

The bush with its PMI in the graphics window

render of the graphics window

same

5.3% of the view shows the part (an occupancy check: something is drawn; the shape itself is checked by its geometry)

T15

PMI > STEP with PMI: the bush and its PMI as STEP AP242 data

ribbon 'PMI › Exchange > STEP with PMI', the file name typed, MB2 = OK

differs

schema AP242_MANAGED_MODEL_BASED_3D_ENGINEERING_MIM_LF; datums A, B (2 datum systems); sizes: 2 diameter, 1 thickness; locations: 1; with ± tolerances: 3; fits: H7, k6; geometric tolerances: 1 coaxiality, 1 perpendicularity; read back by OpenCASCADE: {'datums': 2, 'dimensions': 4, 'geometric_tolerances': 2}. NX writes PMI to STEP AP242 too; FreeCAD’s own STEP export drops it. The envelope Ⓔ and the ISO 2768 note have no semantic AP242 form in OpenCASCADE and are listed as not written

T16

Drafting: New Sheet, a top view and a front view at 2:1

Ctrl+Shift+D, ribbon 'New Sheet', twice 'Base View' with the body selected

differs

the second Base View stands in for a projected view, as in tutorial H

T17

Inherit PMI on each view: the dimensions with their ISO classes and the envelope, the frames, the datum symbols, and the tolerancing note

each view selected + ribbon 'Drafting > Inherit PMI'

differs

4 dimensions [8.0, 16.0, 25.0, 30.0] (⌀%.3w k6 Ⓔ; ⌀%.3w H7 Ⓔ; %.2w; %.2w), 4 symbols, note ['Tolerancing ISO 8015', 'General tolerances ISO 2768-mK']. NX inherits PMI from a model view into a drawing view; FreeCAD has no PMI, NXStyle adds both

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.

What differs from NX

NX places each PMI with a click; here a PMI is placed beside its face. This bush’s PMI are made with no work view, so they show in every model view; tutorial Y works in model views.
NX has no ISO 8015 check and no inspection plan; NX-Style’s come from the PMI’s semantics.
NX writes PMI into STEP AP242 and JT; NX-Style writes STEP AP242 with semantic PMI only (no graphical PMI, no JT).