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How to use GD&T in GOM Software


With its focus on functionality and fit, GD&T is a powerful inspection tool that helps reduce waste and scrap, simplify inspections and create easy to interpret results. GOM Software provides access to the full breadth of GD&T inspections that take only seconds to fully implement within the software. Keep reading to learn where these tools are located in the software and how to use them through several different examples.


Where can GD&T Be Applied in GOM Software?

This tutorial uses a plastic multimedia part in GOM Software. There are multiple areas where GD&T can be applied in GOM Software, and the easiest way is with the GD&T quick creation tool. Begin by opening a new project, importing both the CAD and the mesh data, and applying a prealignment. The GD&T quick creation menu is in the toolbar of the inspection workspace. Clicking on it reveals a complete list of all the GD&T inspection elements that can be created.



The second location for applying GD&T inspection is in the I-Inspect wheel. To bring up the I-Inspect wheel, click on the magnifying glass in the workspace toolbar, or hit CTRL and right-click anywhere in the 3D view, and it will appear at the location of your mouse. If you have an element created and selected, such as a plane, clicking on the GD&T symbol will reveal inspections related to the element. 


Finally, the last place to locate GD&T inspection is in the dropdown menu located at the top of the software. Clicking on inspection and then hovering over check GD&T reveals a complete list of potential GD&T inspections.


Creating and Applying GD&T Inspection to a Project in GOM Software

The easiest way to apply GD&T to projects is with the GD&T quick creation menu. Start by creating some simple form GD&T call outs that don't require a datum system, such as roundness and flatness. The remaining form inspections would also have a similar creation sequence.


First, make the CAD exclusive. Left-click on the CAD, press the letter E, and the software will hide everything but the CAD. For roundness, navigate to GD&T quick creation and click on roundness. At the bottom of the screen, the software indicates what options are available while this function is active.


Hit CTRL and click on a cone, then use the GD&T quick creation tool to construct the nominal element and apply the appropriate measuring principle. The software will then prompt the roundness inspection, so apply a tolerance such as 0.1 millimeters and create and close by hitting OK. The quick creation function is still active, so a few more roundness inspections can be created by hitting CTRL and left-clicking on a cone, then hitting OK. After repeating the process on the desired areas, finish the roundness inspection by pressing the right mouse button or hitting Escape to cancel.


Roundness inspection can be visualized by turning on color representation in the Properties tab. Clicking on the roundness labels and hovering on the right-hand side will reveal double arrows that show the Properties tab when clicked, or you could press Tab, which is the hotkey that's the default for hiding and displaying the properties.


With the roundness selection, navigate to the Display tab, click on it, and then toggle Show Color Deviation Representation and untoggle the Show Tolerance Zone/Virtual Condition. Notice that the software indicates the roundness with the colors that appear. To better visualize it, hide the CAD using the I-hotkey and then click on the mesh and toggle the visibility. To eliminate the nominal elements, such as the Cone 1, Cone 2, and Cone 3, click on each cone's roundness and then go over to the label on the right-hand side, click on Label and then give them a separate label template. For this example, switch it to checks. Now that the element and the inspection element no longer share a common label, they'll be separated. Clicking on all three of the cones and pressing the hotkey E will hide them. Finally, change the tolerance legend to plus or minus 550 microns to scale up or scale down and visually see the areas in or out of roundness.


How to Inspect Flatness in GOM Software

To begin inspecting flatness on the surface using the same process to visualize the high and low areas on the mesh, first make the CAD exclusive. Then find flatness using GD&T quick creation by clicking on it, holding down CTRL, and then hovering over a plane or area. By left-clicking, the software will build the plane and allow a tolerance to be applied. Apply a tolerance of 0.2 and then hit OK and hit Escape to exit out of the function.


Next, to visualize this area, click on the flatness inspection and pull up the Properties tab. Then go down to the display, turn on Show Color Deviation Representation, and then turn off the tolerance zone. Since this is built on the mesh, hide the CAD and then make the mesh visible to see the areas that are red and blue based on the legend scaling.


To get rid of the nominal plane or element, click on the flatness check, press Tab, go to Label and change the template of the label to Checks which will separate the two. Then the plane can be hidden. Scaling the legend to 0.2 provides a better area to see where it's high and low on the mesh.


How to Create a Datum System and Use it for GD&T Inspections in GOM Software

To create a datum system to use for GD&T inspections in GOM Software, begin by making the CAD exclusive. Then create a simple three plane datum structure by clicking on the GD&T quick creation dropdown at the top, and click on Create Datum System. A dialog box will pop up, prompting you to define the elements for the datum structure. Datums on the CAD can be defined by clicking the blue icon in the datum line called Create Fitting Element and then pressing CTRL and left-clicking on the surface that you want the datum.


The software will then create the elements. Then, give each datum a name, such as "Datum A." Then repeat these steps for Datum B as well as Datum C. Once you've created all the datums, you can hit Create and Close to see the datum system listed in the Explorer tab under Actual Datums. If the elements were created ahead of time, for instance, D 1, D 2, and A, you will be able to create a datum system from this. Set Datum 1 as Plane A, then set Datum 2 as a compound structure of D 1 and D 2, then hit Create. For practice, create one more datum system A, B and then hit Create and Close.


How to Use Free Form Surfaces as a Datum Structure in GOM Software

It's common practice to set up and inspect your datum structure as one of the first steps to laying out an inspection plan. For example, if there is an outer contour area as Datum F, you could create a datum system and reference that as the datum, and where the datum falls and dictates how many degrees of freedom it constraints. For example, a freeform surface will constrain all six degrees of freedom if it is your primary datum. If it were the second or tertiary datum, it would constrain the remaining degrees of freedom left in your datum structure.


How to Apply Orientation GD&T Inspections in GOM Software

Beginning with a parallelism check to the interface of the sliding channel to the opposing face, which is, in this case, Datum E, first go to GD&T quick creation, click on parallelism and then hold down CTRL and left-click on the desired surface. The software gives you the choice of ISO 1101 or ASME. For this example, pick ISO. Then select a datum system from the list. It doesn't have to be a particular datum system; you can reference an element such as the plane or Datum E. After the datum system is selected, apply a tolerance of 0.2, and then Create and Close. Once this is done, you can continue applying additional parallelism inspections.


How to Use the Perpendicularity GD&T Inspection in GOM Software

Another simple GD&T inspection is perpendicularity. If you go to the GD&T quick creation and click on perpendicularity, you can check the perpendicularity of Datum E to Datum A and check the most recent slider to Datum A as well. If you press down CTRL and left-click on Datum E, you can choose the datum system. For this example, pick A and then hit OK.


This perpendicularity check can be repeated by holding down CTRL and left-clicking on Plane 4. Then, press and click on Datum A, apply a tolerance of 0.2, and hit OK. Right-click to get out of the perpendicularity creation function.


How to Perform True Position Inspection Requirements in GOM Software

If you have an existing feature, such as Cylinder 1, you can still use the quick creation tool on it, but first, to use the MMR, you'll need to do a linear size check on the cylinder. Begin by going to Explorer, clicking on Cylinder 1 while holding CTRL, and clicking on the CAD, pressing E to make it exclusive. Then go to GD&T quick creation, click on Dimension (Independency Principle), and then use CTRL and left-click on Cylinder 1. The box opens and prompts you to enter a tolerance. For this example, set it to one millimeter and hit OK.


The inspection line that appears on the cylinder label has an upper and a lower limit defined by the linear point size, known as the LP, and this is the method the software uses to calculate the size of the cylinder. When you right-click and edit the creation of this linear size check, you'll see there's an upper limit, a lower limit, as well as the computation. When you click on the computation method, you can see different ways of calculating the upper or the lower limit, such as the maximum inscribed or the minimum circumscribed, depending on the print and the call out.


Hit cancel and leave it as the Two-point size as that is the default correct method. Exit out of that window, go back to quick creation and find true position, which the software calls position. Then CTRL and click on the Cylinder 1 label, select the datum system, ABC, change your tolerance region type to circular, and then apply the MMR. The software will pull the value from the size check applied earlier. If you change the material requirement to none, you'll see in the box for the check that the position fails; but by applying this MMR, the true position passes. Keep the tolerance at 0.2 and then hit OK.


How to Create a Composite Tolerancing Call Out in GOM Software

Another powerful inspection tool in the software is composite tolerancing. Suppose a pattern of holes or cylinders needed to be inspected simultaneously, such as for an assembly fit. In that case, you could create an element group of those cylinders, apply a theoretical exact dimension or TED pattern call out, and then apply a composite tolerance to that inspection. Then both the pattern locating tolerance zone framework and the feature related tolerance zone framework can be applied to create two TED pattern call outs.


Begin with a set of elements that need the TED pattern inspection. This example will use the cylinders already created, C 1 through C 7. Create one element group by highlighting all seven cylinders, then go to the Inspection dropdown menu, and go down to Create Element Group. Give it a name, such as Pattern 1, and hit Create and Close. This element group is now connected to all seven of the cylinders.


Next, go to GD&T quick creation, go down to TED pattern, and then use CTRL and click on the Pattern 1 label. The creation dialog box will open, and then you can begin filling in the needed areas. For this example, give it the name PLTZF, which stands for Pattern Locating Tolerance Zone Framework, and then set the datum system to ABC and the zone type to circular. Don't check the box for material requirement this time. Next, click on the composite tolerancing line, toggle Use Composite Tolerancing, apply a tolerance of 0.25, and then Create and Close.


The next TED pattern inspection will be the feature-related tolerance zone framework that will be named FRTZ. Hit CTRL and click on Pattern 1, choose the datum system to be just AB, and change the tolerance zone to circular composite. Click on Use Composite Tolerancing, hit the toggle FRTVF, and change the name to FRTZF. Then apply a tolerance of 0.2 and then hit Create and Close. The PLTZF and the FRTZF are now checked within element group Pattern 1 as indicated by the name within each line.


How to Perform a Surface Profile Call Out within the GOM Software

To perform a surface profile call out within GOM Software, make the CAD exclusive and expand the GD&T quick creation dropdown. Then hit Select on Surface Profile, and the software will prompt you to select an area upon which to build the inspection. Hold down CTRL and click on a patch on the CAD, and after a moment, the Surface Profile Check dialog box will appear. Choose ISO 1101, select datum system ABC, apply a tolerance of two, and hit OK.


If you need to inspect more than one patch at a time, such as along the opening of an edge, keep the surface profile inspection active and hold down CTRL and Shift to select multiple different patches that the software will use when it builds the surface profile. When you're done selecting all of the desired patches, press CTRL and left-click on a patch to build the surface and allow you to inspect the surface profile. Keep the same standard, the ISO 1101, and then choose the datum system ABC, keeping the tolerance at two millimeters.


If you need to apply an unequally disposed tolerance zone, the option is at the bottom of this dialog box. Clicking on it allows you to choose either the ISO or the ASME standard. If you select the ASME standard, you'll see the label modified to reflect the unequally disposed tolerance, so that won't be used for this example. Hit OK to finalize the creation of surface profile along different patches.


How to Visualize Deviations of the Surface Profile in GOM Software

Lastly, visualize the deviations of the surface profile by following the steps from the previous inspections. Click on the surface profile of the label highlighted in gray, go to Properties by pressing Tab, go to display on the right-hand side, and turn on Show Color Deviation Representation. Color might show up, but it's currently hidden by the surface body and by the CAD body. While clicking CAD, press I to turn it invisible. Then click on both the Surface 1 label and Surface 2 label, navigate to Display Properties and go to Transparency. Toggling it to the right will hide the surface. Now the colors are visualized, and you can turn on the mesh and see the surface profile on the part.


How to Use ISO Visualizations in GOM Software

The ISO visualizations were introduced in the GOM Software version 2020, allowing you to change the display or labels to reflect the appearance on a print. Begin by clicking on the surface and the surface profiles on both of the inspections, and then pull up properties on the right-hand side and go to the label tab. Go to the template and notice there are different options for toggling the display.

By switching to ISO, you'll see the label now change in the 3D view. There is an option for ISO symbology that you can edit, toggle on or off, or adjust to hide the actual values. The option Tendency is the green or red arrow indicating what direction the deviation applies relative to where it should be. If you want to change the position of these labels, you can edit the annotation by clicking on the button marked Edit Annotation Plane, which brings up a window allowing you to choose which plane it is on. In this example, selecting Plane X flips the label, so it's looking in towards Plane X, and then you can change the Reading Direction and hit OK to finalize the label modifications.


How to Learn More about GD&T

You can always utilize the Direct Help menu at the top right of the screen by clicking on it, typing in GD&T, and hitting enter to reveal all the elements related to GD&T. Clicking on General Information About GD&T will provide an overview of what it is and how the standards are calculated. For a more generalized overview, click on Check GD&T to see additional parameters and inspections available to explore, such as the location, symbols, and explanation of flatness and how it's calculated.


Continue Improving Your Digital Engineering Skills with GOM Software

GOM Software contains many user-friendly functions with a full suite of GD&T functionalities. With this powerful software, anyone can perform a quick analysis of their parts from basic cylindricity call outs to full composite tolerancing of a whole pattern-- and this is just one of the many uses for GOM Software. To learn about other applications and functionalities of the software, or to discuss ATOS 3D scanning technologies, contact a Capture 3D team member today!

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