# Datum Reference Frame Definition Template

> Source: https://netray.co/tools/datum-reference-frame-definition-template
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

A one-page record of how datums A, B and C are established, which degrees of freedom they constrain and how the fixture and CMM should locate the part.

## Category

engineering-plm

## Industry

Discrete Manufacturing

## Audience

- Design engineer
- Quality engineer
- CMM programmer
- Tooling engineer

## Tool

**Kind:** template

**Output:** document

**Fields:**

#### Company name

**Key:** company

**Type:** text

**Default:** Acme Precision Ltd

#### Part number and revision

**Key:** part_no

**Type:** text

**Default:** PN-48213 Rev C

#### Date

**Key:** date

**Type:** date

**Default:** 2026-10-20

#### Prepared by

**Key:** author

**Type:** text

**Default:** M. Iyer, Manufacturing Engineering

#### Primary datum A feature

**Key:** datum_a

**Type:** text

**Default:** Mounting face, planar surface (3 points of contact)

#### Secondary datum B feature

**Key:** datum_b

**Type:** text

**Default:** Bore B1 diameter 25 H7, axis (4 DOF with A)

#### Tertiary datum C feature

**Key:** datum_c

**Type:** text

**Default:** Side slot, width 8 mm (rotation about B)

#### Simulator for A

**Key:** sim_a

**Type:** text

**Default:** Ground fixture plate, flatness 0.005

#### Simulator for B

**Key:** sim_b

**Type:** text

**Default:** Expanding mandrel, 25.000 mm nominal

#### Material condition on datum B

**Key:** mod

**Type:** select

**Options:**

- RFS (regardless of feature size)
- MMB (maximum material boundary)
- LMB (least material boundary)

**Default:** RFS (regardless of feature size)

#### Fixture and setup notes

**Key:** notes_in

**Type:** textarea

**Default:** Clamp on rib R2 only, torque 3 Nm, to avoid distorting the bore.

**Blocks:**

#### Datum Reference Frame Definition

**Body:** Company: {{company}}
Part: {{part_no}}
Prepared by: {{author}} on {{date}}

#### Datum features and simulators

**Table:**

**Columns:**

- Datum
- Feature on part
- Physical simulator
- Degrees of freedom constrained

**Rows:**

**0:** A (primary)

**1:** {{datum_a}}

**2:** {{sim_a}}

**3:** 1 translation, 2 rotations

**0:** B (secondary)

**1:** {{datum_b}}

**2:** {{sim_b}}

**3:** 2 translations

**0:** C (tertiary)

**1:** {{datum_c}}

**3:** 1 rotation

#### Material condition modifier on B

**Body:** {{mod}}

#### Fixture and setup notes

**Body:** {{notes_in}}

#### Approvals

**Signatures:**

- Design engineer
- Quality engineer
- Tooling engineer

**Notes:** The datum precedence A, B, C and the six degrees of freedom model follow common GD&T practice (ASME Y14.5 and ISO 5459 describe the rules). Verify against the standard your drawing cites.

## Content

**Intro:** A datum reference frame is the coordinate system every position, profile and runout tolerance on the drawing is measured from. When the shop, the CMM and the design disagree about how to hold the part, the same part can measure good and bad. This template records the scheme once.

**Sections:**

#### How to use it

**Body:** Name the real feature that establishes each datum, the physical simulator you will use to contact it (plate, mandrel, collet, soft jaws) and which degrees of freedom each datum removes. A part has six: three translations and three rotations. The primary datum usually removes three, the secondary two and the tertiary one. Share the sheet with tooling and the CMM programmer.

#### Reading the datum precedence

**Body:** Order matters. A, B, C is not the same as B, A, C because the primary datum gets first contact. The material condition modifier on a datum feature of size changes whether the simulator is fixed at size or can float, which affects shift and therefore measured position.

**Bullets:**

- Primary: most stable, usually a large planar face
- Secondary: constrains location perpendicular to the primary
- Tertiary: stops the last rotation or translation
- RFS simulators expand or contract to the actual size of the feature

#### Common mistakes

**Body:** Drawings sometimes name a datum that cannot physically be contacted, or the shop fixture locates on features different from the drawing datums. Both create arguments at final inspection. Also check that clamping does not distort thin features before you measure.

**Cta:** If your ERP routings do not carry the fixture and setup information, we can discuss attaching setup documents to operations.

**Faq:**

#### What is a datum reference frame?

**Answer:** It is the set of up to three mutually perpendicular planes established by datum features in the order given in a feature control frame. All the related tolerances are measured relative to it.

#### What are the six degrees of freedom?

**Answer:** Translation along and rotation about each of the three axes. Datums A, B and C together remove all six, so the part location is fully defined.

#### Do I always need three datums?

**Answer:** No. A feature may need only one or two datums depending on which orientation or location it controls. Use as many as the function requires.

#### What is a datum feature simulator?

**Answer:** It is the real equipment surface, such as a gauge plate or mandrel, that stands in for the theoretically perfect datum during measurement.

## Search terms

datum reference frame template, datum definition form, datum feature simulator, datum scheme documentation, gd&t datum setup sheet, fixture locating scheme template, datum targets worksheet

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