What is GD&T?

GD&T is an acronym that stands for Geometric Dimensioning and Tolerancing.  It is a symbolic language used by designers to communicate manufacturing constraints and tolerances clearly.  This information is conveyed in the form of annotations included in the design of the part.

To start, the designer encodes the information into the model, using GD&T’s specific grammar and syntax rules.  This eliminates the lengthy notes in a drawing that used to be used to describe the form.  With GD&T we have a broad range of tolerances, giving the designer a certain flexibility to communicate dimensional constraints based on the requirements of the part. Read More


How to Evaluate Flatness in GD&T

Flatness ASME GD&T Definition

In this post, we are going to take a look at the multiple methods of evaluating flatness in GD&T and determine which is the optimal approach.

Flatness is a GD&T form tolerance that is conceptually simple.  According to the ASME Y14.5 standard, it “specifies a tolerance zone defined by two parallel planes within which the surface must lie.” Read More


BuildIT 2016 SP2 is Now Available!

Service pack 2 for BuildIT 2016 is now available for download. Please view the full release notes for more detailed information.


  • Modified the surface highlighting during inspection to preserve all other rendering settings (mode, transparency…).
  • Added the ability to set the threshold for the geometry identification at import (Simplify Quadrics).
  • Read More

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    GD&T in Wind Power: Maximum Material Condition and Maximum Material Boundary Effects on a Wind Turbine Tower Flange

    Wind Turbine Flange GD&T

    In a previous post, we presented an application of geometric dimensioning and tolerancing with a wind turbine flange. In this text we will continue further, analyzing the same part with simulated points. Our objective is to observe the effects of different material modifiers on the analysis results and their advantages. For this, we will simulate measurement points on the part and then perform a GD&T analysis in BuildIT. We will then compare how the results obtained are affected by the application of different modifiers. Read More

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    GD&T in Aerospace Assembly: Use of Multiple Datum Targets for N-2-1 Location of Fuselage

    Datum Based Alignment of Fuselage

    This post will present a possible case in the aerospace industry for locating a fuselage part with 9-2-1 location, using datum target areas. For more detailed information on datum targets, you may refer to the ASME standard, section 4.24 [1].

    N-2-1 Location with Datum Target Areas

    In a previous post, we talked about using 3-2-1 precision location to create an accurate and repeatable datum reference frame for the part, while avoiding overconstraint. However, for most sheet metal manufacturing processes, the main dimensional problem is the sheet metal deformation normal to the surface [2]. This deformation cannot be neglected, even under the self-weight of the workpiece. Analysis shows that the average deflection of a sheet steel plate 400 mm x 400 mm x 1 mm under its self-weight can be between 1-3 mm with a 3-2-1 location layout. Therefore, an adequate fixturing system for sheet metal usually requires N>3 locators on the primary datum to properly restrain workpiece deformation. Read More

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    GD&T in Wind Power: Position Tolerances in Wind Turbine Tower Flanges

    NX Flange Full

    Recently, utility-scale wind turbines have become so large and heavy that they are manufactured and assembled in sections. While a wind turbine tower can reach a height of up to 100 m, there is a limit of 4.3 m on the diameter to pass under bridges. For easier handling and transportation, a wind turbine tower is typically manufactured in multiple sections. Read More

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    GD&T in Automotive Assembly: Surface Profile Tolerances

    Car Door Surface Profile Tolerances

    In a previous post, we presented an application of datum targets for 3-2-1 location of a car door. In this post, we will follow up with the same part to verify the surface profile tolerances along the side surfaces of the door, for optimal assembly conditions.

    Surface Profile Tolerances

    A surface profile tolerance zone is a three-dimensional volume establishing permissible boundaries of feature(s) of a part. A surface profile tolerance can be used to define a tolerance zone to control combinations of size, form, orientation and location of a feature relative to true profile.  For additional information about profile tolerances, please refer to the section 8 of the ASME Y14.5-2009 standard [1]. In Figure 1, we can observe the car door part located through datum targets with surface profile tolerances. In the next sections, we shall analyze these tolerances further to better understand their functions. Read More

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    GD&T in Precision Engineering: Use of Diamond Pins in Precision Location Applications

    Diamond Pin Assembly GD&T

    In a previous post, we elaborated on the principles of precision location and presented one of the techniques for achieving it: The use of slots. However, with slots, we can still have the problem of high manufacturing cost if the part has substantial thickness.  This is because manufacturing a slot is simply more complex than drilling a hole, in relatively thick parts. One technique to have the best of both worlds is to use diamond pins. Read More

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    GD&T in Automotive Assembly: Use of Datum Targets for Precision Location of Large Surfaces

    Automotive Datum Targets

    In manufacturing and assembly, parts must be accurately and repeatably located in a well-defined reference frame to ensure consistent quality. For many automotive parts, because of the large and irregular surfaces involved, the entire surface of the feature cannot be used as a datum. In these cases, we use datum targets to establish a datum reference frame. This post will present a possible case in the automotive industry for locating a car door with the 3-2-1 location method, using datum target areas. For more detailed information on datum targets, you may refer to the ASME standard, section 4.24 [1]. Read More

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    GD&T in Precision Engineering : Use of Slots in Precision Location Applications

    GD&T Pin and Slot DRF

    Precision location can be very important in various engineering applications, such as machining and assembly. In machining, the tool follows a very precise path and a workpiece must be located precisely and stably at a precise position. In assembly, the positions of assembled parts must be assembled easily and overconstraint of the parts must be avoided. One of the common techniques for accomplishing these targets is the use of slots as part features. Read More


    BuildIT 2016 SP1 is Now Available!

    Service pack 1 for BuildIT 2016 is now available for download. Please view the full release notes for more detailed information.


  • BITS-2461 Modified the model import where GD&T Features will not be imported if their associated geometries are not imported
  • BITS-2919 Improved the object picking in Wireframe mode
  • BITS-2856 Modified the Point Inspection Annotation command to reference the associated Actual Point if no Nominal is found
  • BITS-2944 Added Show Details option for elements of pattern features in the new entity-based reporting scheme
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    Jig, Tool Building and Assembly using BuildIT

    Metrology assisted assembly, as well as jig and tool building, are used extensively in the aerospace and automotive industries. BuildIT can help streamline these workflows by offering all of the necessary tools:
    – real-time inspection capabilities,
    – network bundling for large part inspection
    – and flexible reporting tools. Read More