Zeiss GD & T Pro App Notes PDF

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Zeiss GD & T Pro App Notes Learn, interpret and inspect GD&T according to ISO 1101. Using examples and animations, the GD&T Pro App explains the wide range of geometrical dimensioning and tolerancing in an understandable and simple way. In the Basics section, essential terms are introduced; the Symbolism section explains and illustrates the most common symbols in GD&T.

Basics Introduction Properties of a Part The properties of a part are comprised of geometric, physical and chemical properties. After production, a part has actual properties. Deviations between actual and plan are unavoidable. The functionality of products depends primarily on how much the actual properties of the single parts deviate from the nominal properties. The nominal properties are determined by specifying geometric, physical and chemical properties. The drawing shows the geometric properties through a tolerance dimension and a position tolerance as well as the physical and chemical properties through the material specifications. After production, the part features actual properties. For example, the connecting surface perpendicular to the borehole axis is a cavity that can influence the stability of the part. Such deviation between the actual and nominal properties are generally unavoidable in commercial production. The geometric properties are divided into dimensional and design properties specified by he designer. This occurs in the shape of tolerances. Each individual feature of a part must fall within its specified tolerance in order for a part to work properly. The goal of this teaching program is to familiarise you with the form and position design tolerance. Furthermore, the connection between the size, form and position tolerances will be illustrated.

Design Errors Design errors can be broken down into position and form errors, waviness and surface roughness. A workpiece surface is always an overlay of these design errors. Shape deviations can be divided into position deviations, form and waviness deviations and, surface quality. Possible causes for these deviations are shown in the right column. A workpiece surface is practically always an overlay of given shape deviations.

Classification of Geometry Tolerances Geometry tolerances can be broken down into size and design errors. Design tolerances can be further broken down into position, profile an form tolerances. This illustration provides an overview of the design tolerances that belong to the geometric tolerances in addition to the dimension tolerances. Over the cause of the teaching program you will become familiar with all form tolerances profile form tolerances and position tolerances. Furthermore, you will receive information on various tolerancing possibilities. Now it is time to get an overview of the form and position tolerances, specifically the breakdown of position tolerances into directional and runout tolerances.

Drawing Entries Symbolism Symbolism is clearly specified for form and position tolerancing. The tolerance box has at least two, but no more than fives boxes. The tolerance value is entered in millimetres (mm).

2

5

The symbols are clearly specified for form and position tolerancing. The tolerance frame has at least two but no more than five boxes. In general it is always read from left to right. The first box always contains the symbol of the tolerance property. For example, there is a circle for the roundness tolerance, a parallelogram for the flatness tolerance, or a circle with a plus sign for the position tolerance. The second box shows the form or position tolerance value in millimetres (mm). For example, the 0.02, 0.05 or 0.3 millimetres. The third to fifth boxes are used to enter the datum letters for the position tolerances. For a tolerance zone with a circular cross section, for example, cylindrical tolerance zones, the diameter symbol is entered in front of the tolerance value. If the form and position tolerance will apply to multiple features, it can be indicated above the tolerance box. For example, six times. If special properties are required, this can be noted near, preferably below, the tolerance frame. These include the type of form deviation for the flatness tolerance. NC – not convex.

Application The tolerance box is linked to the tolerance feature by a leader line with arrow.

The tolerance frame is linked to the tolerance feature by a leader line with arrow.

If a datum is required for tolerancing, it must be indicated with a datum triangle and a framed datum letter. This datum letter must also be entered in the third box of the tolerance frame.

If the arrow is drawn with the extension of a dimension line, the axis or midplane is the tolerance feature. In this example, the straightness deviation of the axis of this shaft is toleranced.

If the leader arrow ends next to the dimension line, the surface line or surface is toleranced. In this case, the straightness deviation of each surface line is toleranced.

If a common datum comprised of multiple features will be used, these features must be specified as datums with different datum letters. A common datum is identifiable by the way it is entered in the tolerance frame. The datums are located at the end of the tolerance frame and are separated by perpendicular lines. In this example, the common axis must be created from A and B. If axis or midplanes are used as datums, the datum triangle must be given as an extension of the dimension line.

A datum structure system is created from several datum features. Up to three boxes with different datum letters are located in the tolerance frame. These datum letters must be entered with border and datum triangle on the specified datum elements. The order of the letters is important. The first letter is always the primary datum, the second the secondary datum, and the third the tertiary datum. In this order, the primary constrains three degrees of freedom, the secondary constrains two degrees of freedom, and the tertiary datum constrains one degree of freedom. If exact dimensions are theoretically required in a drawing, these are labelled with a numerical value in a square. Theoretically exact dimensions are required for the position, profile and directional orientation tolerances.

Applicable Area Form and position tolerance apply to the entire expansion of the toleranced feature. However, the scope of validity for form and position tolerances can be limited. Form and position tolerances apply to the entire expansion of the toleranced feature. The scope of validity for form and position tolerances can be limited. This is done by labelling and dimensioning the size and position of the limited area.

Only a certain area of a feature influences the function. The datum axis A, in this example, is only relevant to function in an area of 15 mm. The drawing entries must clearly specify this area using a dot-dash line and the theoretically exact dimension of 15mm. The axial runout tolerance only applies to the limited part of the plane surface. This limited part of the plane surface is identified through a dot-dash line and the theoretically exact diameter of 20mm. If the tolerances must be complied with globally and locally, they must be entered as follows: a global flatness tolerance of 0.1mm applies to the entire expansion of the surface, at the same time, however, a flatness tolerance of 0.05 applies to every local partial surface of 100x100mm.

Limitations Form and position tolerance apply to the entire expansion of the toleranced feature. In special cases, it can be necessary to enter the area being toleranced outside the part.

Form and position tolerance apply to the entire expansion of the toleranced feature. In special cases, it can be necessary to enter the area being toleranced outside the part. This is done through the use of projected tolerance zones. These are labelled by a circled “P” behind the tolerance value in the tolerance box and on he linear dimension of the projected tolerance zone. The position tolerance does not apply here for the disk thickness of 18mmm, but for the area of 20mm outside the disk.

More Tolerances Multiple form and position tolerances can apply for one feature. If multiple form and position tolerances will apply for one feature, multiple tolerance boxes can be stacked on top of one another. These are then linked to the toleranced feature by a common leader arrow.

Reference Systems Datum A theoretically exact geometric reference (such as axes, planes, straight lines, etc.) to which toleranced features are related. Datums may be based on one or more datum features of a part. Straight axis

Plane

The datum is always a theoretically exact geometric element, such as a straight axis or a plane.

A datum letter identifies the datum element to which the respective position profile tolerance refers. The datum letter is a capital letter entered in a datum box that is also given in the tolerance frame. The datum box is connected to a datum triangle by a leader line.

If an axis midplane is to be used as a datum, the datum triangle must always be entered as an extension of the corresponding dimension line – even if the affected tolerance dimension already exists at another location.

However, if a surface or surface line is the datum, the drawing entry appears as follows: The datum triangle must always be clearly offset from the dimension lines, dimension auxiliary lines and edges. After finishing the part, a theoretically exact datum must be created from the datum element featuring form deviations. This is done by eliminating the form deviations of the datum elements.

If the datum is a line or a plane, it must be placed so that the greatest distance between the datum and the captured datum element is kept to a minimum.

If the datum is the axis of a borehole, it is used as the axis of the largest inscribed cylinder. This is the maximum inscribed cylinder.

With a shaft, the datum is the axis of the smallest circumscribed cylinder. This is the minimum circumscribed cylinder.

If the datum is the centre plane of a groove, it is used as a centre plane of the inscribed parallel plane pair with the greatest distance. Maximum inscribed plane pair.

If the datum is the centre plane of two exterior surfaces, it is used as a centre plane of the circumscribed parallel plane pair with the shortest distance. Minimum circumscribed plane pair.

Common Reference Combined datum out of two or more separate datum features. If a common datum is comprised of two or more form elements, the datum letters are given in the third field of the datum box and separated by perpendicular lines. In this example, the datum is the common axis or the two minimum circumscribed coaxial cylinders that must be formed simultaneously from the left and right shaft sections. This rule is explained in more detail as follows:

If only the left cylinder is available as a single datum element, the datum is the axis of the minimum circumscribed cylinder with diameter 𝑃1 , the pairing dimension of the left shaft section. It is the same if the right cylinder is the only datum element (diameter 𝑃2 ). This would be the case if neither axis is coaxial.

If the axis of the left minimum circumscribed cylinder is selected as the common datum, it results in a circumscribed cylinder with diameter 𝑃2∗ for the right shaft section, which is considerably larger than its pairing dimension 𝑃2 .

Likewise a larger circumscribed cylinder results for the left shaft section if only the axis of the right minimum circumscribed cylinder is selected as the common datum.

The common axis must now be created is a way that both circumscribed cylinders have to be enlarged as little as possible. The diameter of the minimum circumscribed coaxial cylinders created in this manner is described as effective pairing dimensions. They characterise the functionally effective counterpart with a common axis.

If form deviations on the datum surfaces are negligible, the common datum axis can be said as the axis of the minimum circumscribed cylinder around the axis of the two individual minimum circumscribed cylinders.

Datum System A group of two or more separate datums used as a combined reference for a tolerance feature. Form and position tolerances often require definition of a datum system comprised of up to three datums in order to clearly specify the location and direction of the tolerance zones. The principles of the three plane datum systems apply: primary datum, secondary datum, tertiary datum.

Primary Datum

Datum A is the primary datum because datum A is in the first position in the tolerance frame. The primary datum must be added to the datum element so that the greatest distance between the datum and datum element is kept to a minimum.

Secondary Datum

The secondary datum must be positioned perpendicular to the primary datum. Taking this into consideration, the greatest distance between the secondary datum and the secondary datum element must also be kept to a minimum.

Tertiary Datum

The tertiary datum must be positioned perpendicular to both A and B. The part is now only moved in the direction of datum C until it lies on at least one point on C. The part is now in a clear position to the datum system.

Standards There are numerous standards for tolerancing (ISO and DIN).

Symbolism Straightness Overview Tolerance Type

Form

Elements

Line, Axis

Datum

None

Introduction

Straightness Tolerance of an axis The tolerance zone is enclosed by a cylinder with diameter 𝑡. Straightness Tolerance of an edge The tolerance zone is enclosed by two parallel, straight planes at distance 𝑡. Straightness Tolerance of a surface line Each surface line of the toleranced cylindrical surface must be enclosed by two parallel straight lines at distance 𝑡.

Example: Straightness 1 Straightness tolerance is a form tolerance. Straightness tolerance, 0.5 mm, in the example applies to the entire length of the part in every cross section. This tolerance is used to establish a tolerance zone that is bordered by two parallel lines at a distance of 0.5 mm. The respective captured must lie within this tolerance zone if the part is to comply with the tolerance.

Form deviations are evaluated using the minimum zone evaluation method. For example, the distance between two ideally aligned geometric elements which enclose the captured surface must be as small as possible. This distance between them is the form deviation. The determination of straightness deviation will be explained on the basis of any section.

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Straightness deviation of the displayed feature , is seen as tolerance compliant when the captured profile can be fit in between two parallel lines whose distance is less than or smaller than the specified tolerance. Practically, this means that two parallel lines must be found, which enclose the captured profile with the least possible distance. This minimum distance is the sought after straightness deviation.

Example: Straightness 2 On parts such as this edge or blade, it is often enough to limit the straightness deviation in one direction only. This is referred to as straightness deviation in the specified direction. The straightness deviation of the edge, is the minimum distance of two parallel planes lying perpendicular to the tolerance direction, which includes the documented edge.

These tolerance specifications also apply to the straightness deviation in the specified direction. Each documented surface line of the cylinder must lie within two parallel planes with a distance of 0.07mm to ensure that straightness tolerance can be complied with.

Example: Straightness 3 This guide bar will be used to limit the straightness deviation of the documented axis in two directions. The straightness tolerance in the width direction of 35mm is 0.2mm. Straightness tolerance of 0.05mm is stipulated in the narrow side of 12mm.

In short, this means that the documented axis must lie in a tolerance cube the length of the guide bar with a cross section of 0.2x0.05mm in order to comply with both straightness tolerances. After production of the guide bar, the axis deviates from its ideal geometric form. It exhibits straightness deviation.

In this example, the straightness deviations are 0.06 and 0.05mm. This means that the straightness tolerance of 0.05mm in the direction of the narrow side of the tolerance cube has been exceeded.

Example: Straightness 4 The tolerance specification for this cylindrical form element, state that the documented axis of borehole must lie within a cylindrical tolerance zone with a diameter of 0.09mm. If axes or mid-surfaces have to be tolerance, the leader arrow must be labelled as an extension of the corresponding dimension line. For straightness tolerances of the axes of rotational symmetric parts a cylindrical tolerance zone must always be stipulated, that is, a diameter symbol must proceed the tolerance value. This is a spatial tolerance deviation because the documented borehole axis may deviate from the straightness in any direction. The actual straightness deviation is the diameter of the minimum circumscribed circle around the documented axis, here it is 0.07mm. You will now see a few more examples of tolerancing axes with cylindrical tolerance zones. As a result of this type of tolerancing, individual cylindrical tolerance zones with the same value can be specified for the axes of several separate cylindrical elements. The individual elements therefore, have cylindrical tolerance zones independent of each other which have the same diameter. On each feature, the leader arrow is entered as an extension of the dimension line because axes are being toleranced. The location of the cylindrical tolerance zones can vary, only their diameters are the same.

Using the same tolerancing, but with the addition of the letters “CZ” – common zone – after the tolerance value, the axes of the cylindrical feature share a common cylindrical tolerance zone within which the documented axes of the individual elements must be located.

Roundness Overview Tolerance Type

Form

Elements

Circumferential Line

Datum

None

Introduction

Roundness Tolerance In the measuring plane perpendicular to the axis, the tolerance zone is enclosed by two concentric circles at distance 𝑡. Example: Roundness 1 Roundness tolerance is also a form tolerance. In this example, roundness deviation of the captured profile will be confined in every cross section of the cylindrical part. The roundness deviation of each cross section must be no more than 0.08mm. This means that the captured circumference lines must lie between two concentric circles that have a radial distance of 0.08mm. The roundness deviation is the minimum radial distance of two concentric circles that tangentially confine the circumferal line.

Example: Roundness 2 A roundness tolerance can also be specified for circular arcs. This information is provided in the same way as for complete circles. The captured circular arc lies between two concentric circular arcs at a minimal radial distance. This distance is the roundness deviation.

Flatness Overview Tolerance Type

Form

Elements

Plane

Datum

None

Introduction

Flatness Tolerance The toleranced area must lie between two parallel planes with the distance 𝑡. Example: Flatness 1 Flatness tolerance is a form tolerance. The captured surface must lie within two parallel planes separated by the amount of the flatness tolerance. ...