Total Runout | GD&T Basics. While straightness has parallel lines representing its tolerance zone, the flatness tolerance zone is formed by two parallel planes. Post by Tom Oakes » Thu Sep 06, 2018 8:16 pm. The part in question is a retaining ring, and the ring is out of round by more than . . This symbol specifies the depth of a feature. So if your center is 0. . Would a concentricity of +/-. Measure concentricity with Dial Gauge: Keep the target in place and put the dial gauge on the top of the circumference for the axis indicating the tolerance. Brett Krienke Posts: 481 Joined: Tue May 22, 2018 7:56 pm Location: Austin, TX Hat sich bedankt: 122 Mal. Concentricity - Concentricity describes a condition in which two or more features (cylinders, cones, spheres, etc. There’s also a taper at the front of the. Runout, roundness, and concentricity. 01mm Concentricity @ MMC of 21/21. Easy Guide to GD&T – Total Runout [ Symbol, Tolerance, Measurement ] GD&T Total Runout Symbol . Definition of Total Runout. San Pedro Street Ste 4 ♦ Gilbert, AZ 85233 USA (480)478-0041 ♦ (480) 478-0041 Fax ♦ An Introduction to Geometric Dimensioning and Tolerancing (GD&T) Michael Yount Proof Engineering Co. The GD&T symmetry callout ensures symmetry control by checking the distance. 025" off and not notice. •The true geometric counterpart’s axis or center line or center plane is the datum. Concentricity is expensive to inspect. If you see a concentricty call out of diametrical tolerance zone of 0. Even if the thru bore and one end bore are done in the same operation with the same tool there could still be issues with concentricity. Concentricity and symmetry are also types of location tolerances. Advanced Search We may lose more than 36% of the tolerance zone by using the callout in this manner. Profile tolerances can be used to control location, but these are covered separately. Figure 26. a shift tolerance is always available c. I thought a concentricity callout was only used on a high speed rotating part application. First, you will have to establish and identify where would the point of the datum plane, surface, or axis lies. To specify geometric tolerance properties, do one of the following: For parts, click Geometric Tolerance (MBD Dimension toolbar) or Tools > MBD Dimension > Geometric Tolerance. Or, can I just get away with using Calypso as is?Manufactured items differ in size and dimensions from the original CAD model due to variations in the manufacturing processes. Verifying concentricity is a time-consuming process, and in many cases it is. Perpendicularity can reference a 2D line, but more commonly it. Your drawing uses 2 surfaces only. This tolerance is similar to concentricity, and the verification of symmetry tolerance is also time-consuming and difficult. These are form, location, orientation, profile and runout. Different source but here is what I had (Attached) Also see p 146 of the ASME 1994 std. Concentricity is concerned with the centre, and the control is associated with a feature of size to indicate it is applied to the axis. In this approach, you can select the smaller outer cylinder to define the feature. 020. Simultaneous position callouts or MMB/MMC, etc. Select the GDT tab. There is a callout that the treads are to run true with centers on the end of the part (other features are also called out to run true with the centers) within . 006. Many people are confused by concentricity callouts. This page explains the 16 symbols used in GD&T, and the classification thereof. I know concentricity is obsolete, but I'm curious how you guys would handle this. 06-18-2009, 02:00 PM. And apparently, it is being phased out of ASME Y14. It looks like a callout exist for that. 1 Position - The position tolerance symbol is a circle with a horizontal and vertical line drawn through the circle. It says that each diameter much be concentric with each other and I was trying to avoid having 4 concentricity callouts for each diameter if at all possible. The callout controls the circularity of the inspected cross-section. Roundness, or circularity, is the 2D tolerance that controls how closely a cross-section of a cylinder, sphere, or cone is to a mathematically perfect circle. How to easily type miscellaneous technical symbols (⌀ ⌖ ⌘) using. 5M ISO At Maximum Material Condition m. No -- do not reference a datum in that profile callout. ⏿. I just wanted to see how you might handle this concentricity callout in this cavity: Pic11. The largest maximum and minimum difference is used as. DATUM -A is the 80mm piston bore. Concentricity | GD&T Basics The datum, or master feature would be the shaft. 01. (Circular) Runout INCLUDES FORM ERROR about the circle. 5 defines a part as. Can you suggest what should be the. The hardware most commonly used with a counterbore is a. A requirement that the centerline or axis of two features are located within a specified tolerance of each other. 002 diameter cylindrical tolerance zone at the center of -A-. Controls the form of a feature. Besides the removal of concentricity and symmetry, the changes in the ASME Y14. Observer eye symbol. A true position of . Next, you will plot the points on the outer profile’s controlled surface, which can be determined using the CMM or a coordinate measuring machine. However, for the first GTOL in the part, the GTOL frame is previewed with. Cylindricity is a fairly common callout for shafts, pins and any critical cylindrical element. The criteria - 0. All the profiles of orientation and are used in the exact same way. png. For more ALT codes for various signs and symbols, see ALT Codes for Miscellaneous Symbols. Older →. png. The GD&T is telling you what the datum is. 05 A O O A O O O It is locating the 0100 cylinder's derived median points relative to the datum axis of the bore. Dont take it personal, we all screw up big at times, My favorite screw up is to be . the print had a very clear concentricity callout for those 2 diameters. ago. In all likelihood what your seniors actually want is true position, not concentricity. Straightness, Flatness, Circularity, Cylindricity, Line profile, Surface profile, Perpendicularity, Angularity Parallelism, True position, and Concentricity callouts can be added to various created entities and shown in the report. cylindricity e none of the above 50 in a concentricity callout. Runout can also measure concentricity for a product. To open this page: With a drawing open, click Options (Standard toolbar), select Document Properties, and then select Dimensions > Hole. Hello JSW05, The main target of my post is ensure that my measurement method for calculating the position callout and concentricity callout is the most correct. The circularity callout defines a two-dimensional tolerance zone for the actual part surface. Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line. Any thoughts on how to get Calypso to measure concentricity per ASME Y14. The shoulder is the ledge between threads and shaft. 1. Fluent with axial and radial stack ups as well as…In this thread, for example, you want to apply concentricity callout to the hole. 1. The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces. This symbol specifies the depth of a feature. Step-2: Plot the controlled surface outer profile using CMM or other measurement instruments. 1 O O 100+0. Lathe backbore - critical features - Challenge. A ground cylinder. Concentricity Gage being used to inspect a part Angularity Measurement • Simple Angle Callout • Use Bevel Protractor – should be anywhere between 29° and 31° Angularity Measurement • Angularity Callout • Tolerance 0. Here you can see that GD & T symbols are broadly categorized into the following categories based on their features. Geometric Dimensioning & Tolerancing ASME Y14. The inspector must take a number of two point measurements (theoretically an infinite amount of them) as shown below. If the case isn’t properly concentric and the bullet isn’t properly aligned down the center of the bore, the bullet will enter. If you see a concentricty call out of diametrical tolerance zone of 0. 3. Concentricity is a 3-Dimensional cylindrical tolerance zone that is defined by a datum axis where all the derived median points of a referenced circular feature must. Turning Point Tutors cc Achieving academic excellence Exam Revision Notes MOW 217 Presenter 1: Benji Gwashavanhu Presenter 2:The thread is 1/2-28 if that matters. Most often they're used incorrectly. HTH (Hope This Helps)Datum Selection. The concentricity value can be calculated by using two diameters — one for the hole and one for the shaft that goes through it. 5? As I understand the standard, it is looking for all of the median points of diametrically-opposed elements of the feature. If required select feature material modifier. 1 dia tolerance cylinder centered on datum [A]. Search in titles only Search in PC-DMIS for CMMs only. Position Tolerance Symbol 3. Many of the common symbols used in technical drawings make use of a graphical callout structure known in the ASME standard as a ‘feature control frame’ (FCF) and in the ISO GPS family of standards as a ‘tolerance frame’. Concentricity is a advanced 3D GD&T call is ensured such one or more component features live concentric about a datum axis. Concentricity considers how a cylindrical shape is positioned on a theoretical axis. Level and origin to that 3D line. 0025 from the center axis of the part as defined. The graph expresses the annual evolution of the frequency of use of the. It says that each diameter much be concentric with each other and I was trying to avoid having 4 concentricity callouts for each diameter if at all possible. --This is not okay per any rev of GD&T. 2. 4. 13. The correct method would be to use the datum as the datum. However, in more. Concentricity Tolerance Zone. ⏿. See screen shot below from the machining program. Concentricity and symmetry are also types of location tolerances. 23FF ALT X. Post by Tom Oakes » Thu Sep 06, 2018 8:16 pm. Transforming CMM Metrology with PC-DMIS Pro, CAD and CAD++ software. V-blocks are not the correct datum simulator. What is the best way to measure this on the CMM and report it?2. 001" but concentricity . These measurements would then need to be compared to each other. 0005 It always ends up . So ideally, both features should share the same true central datum plane. GD&T Flatness is a common symbol that references how flat a surface is regardless of any other datum’s or features. Concentricity treats the mating surfaces as ideal circles, which is ideal for alignment. Symmetry. . You can specify document-level drafting settings for hole callouts. Datum A is a plane. 001? Is this the reason the true position callout is popular on round features, rather than a smaller concentricity callout. 2. I’m making these parts that call for rough and finish reamers, but I’m having trouble holding to the concentricity callout of . 0025’’ lowerthan the center of DBT Hole SizePerpendicularity, Concentricity, and True position callouts may require additional air nozzles, air circuits and multiple input readouts to prevent “out-of-round” conditions from influencing the gage readings. Advanced SearchWe may lose more than 36% of the tolerance zone by using the callout in this manner. Tolerance ,001" ( which is 0,0254 mm ) for those lengths of cylinders it's negligible. For the the complete list of the first 256 Windows ALT Codes, visit Windows ALT Codes for Special Characters & Symbols. Concentricity r r Location Symmetry i i Circular Runout h h For Related Features Runout Total Runout t t . The goal is to ensure it is straight enough for the application. Thus, while straightness only makes sure that a single line on a surface has to be within the limits, GD&T flatness does the same for a collection of. Concentricity. The purpose of a concentricity callout is to ensure that the. Runout. Similar to break edges, deburr callouts are usually pretty loosey goosey. Continuing with the example of the circle, Concentricity controls how much the distance between any median point and the ideal axis may vary, hence it establishes a. I have multiple parts where a cylinder is called out as a datum and another cylinder has either a runout or concentricity callout back to the datum. The callout controls the circularity of the inspected cross-section. I know concentricity is obsolete, but I'm curious how you guys would handle this. Default file types. It is defined as the variance of the surface. If a drilled or reamed hole must run perfectly true to a coaxial counterbore or circular boss, a concentricity callout is the best way to assure this. More Intuitive Workflows for Creating and Editing Geometric Tolerances (GTOLS) in DrawingsGD&T Tips - Runout - vs Concentricity Concentricity (see "when used") What And probably 50 other discussions. We make 'encoder disks' which are disks that have a pattern on them that typically have to be held with a tight tolerance against the ID as204K subscribers in the Machinists community. ” This yielded five results, the first of which is in the Foreword section of the standard. ) It's kind of like checking flatness; the three highest points taken anywhere on those four surfaces form an imaginary plane. Most often they're used incorrectly. Sinclair International has released an interesting article about Case Concentricity* and bullet “run-out”. This area is a cylinder with 0. (Reason: concentricity. Next, the roller body would be rotated in the same setup and have its runout measured in several locations. Tags: None. Total runout c. Concentricity ASME. measure your datum diameter first and set your X and Y scales to 0. To set geometric tolerance properties, do one of the following: For parts, click Geometric Tolerance (DimXpert toolbar) or Tools > DimXpert > Geometric Tolerance. The surfaces must be perpendicular within the tolerance limits specified in the feature control frame. • For workpieces with high concentricity callout • For radial readjustment of workpieces with big changes in weight during machining • To apply additional grip force to the workpiece by the adjustment screws • Readjustment of the centerline of the workpiece in process Technical features • Integrated fi ne adjustment to center the. We can use the above setup and follow the following steps to measure cylindrical part concentricity. png. However in many cases, the use of runout or true position can replace the need for concentricity and be much easier to. The counterbore symbol is used on a drawing to indicate that a counterbore hole feature is required. The reason shooters work with tools and gauges to measure and control concentricity is simple: to make sure the bullet starts down the bore consistently in line with the bore. Unless of course you want two concentric ovals. Total runout is measured by rotating the part 360 degrees around the datum axis and using a dial indicator to see the variation on the part surface. OD/ID Concentricity Callouts. Sometimes called roundness, circularity is a 2-Dimensional tolerance that controls the overall form of a circle ensuring it is not too oblong, square, or out of round. I would have recommended calling the profile of the hex concentric to the shaft, however seeing as most others here seem to be settled on "profile of a surface" I'll have to re-evaluate my understanding of the concentricity callout. 4 mm. Symmetry. 4 to 5. Concentricity ASME. Concentricity is a very complex feature because it relies on measurements from derived median points as opposed to a surface or feature’s axis. Concentricity: The shoulder and thread pitch diameter shall be concentric within 0. 9m Create Account. Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line. runoutLogin here. The following formula is used to calculate the concentricity: C =. The purpose of a countersink is to allow a fastener, typically a flathead screw, to sit slightly below the surface of the part. Step-2: Plot the controlled surface outer profile using CMM or other measurement instruments. Depth of. 005" be within tolerance for your part?Straightness tolerance is a 2-dimensional GD&T callout that controls the straightness of part features. In other words, the GD&T "Position" Tolerance is how far your feature's location can vary from its "True Position". I am using G821 to keep material as close to guide bushing as possible. Creating the GDT Call-out. This control is used a lot in a variety of situations that involve coaxial relationships. Lindenberger. Click to expand. 4. 4. The tolerance of the perpendicularity callout. Surface perpendicularity does not directly control the angle between the surfaces. San Pedro Street Ste 4 ♦ Gilbert, AZ 85233 USA (480)478-0041 ♦ (480) 478-0041 Fax ♦ An Introduction to Geometric Dimensioning and Tolerancing (GD&T) Michael Yount Proof Engineering Co. Usually the cylinder is checked from outside diameter to inside. Concentricity is a condition . png. Concentricity, is a tolerance that controls the central derived median points of the referenced feature, to a datum axis. Total runout controls both the amount of variation in the surface as the part is rotated, but the amount. Chamfers do not have to be a 45 degree angle as shown in the picture above, but this is certainly the most common configuration. I just wanted to see how you might handle this concentricity callout in this cavity: Pic11. We can use the above setup and follow the following steps to measure cylindrical part concentricity. It's boundary and tolerances are relative to the physical edge of the circle, not the axis line. Note that in the case of the 90° countersink, this callout is the same as a 45° chamfer because the countersink angle takes both sides into account, so it is twice the chamfer angle. #6. png. A requirement that the centerline or axis of two features are located within a specified tolerance of each other. Rotate the target and measure the maximum and minimum runout with a dial indicator. Instead, it ensures perpendicularity by. When you project a datum along the axis line, the projected deviation grows. 05 A O O A O O O It is locating the 0100 cylinder's derived median points relative to the datum axis of the bore. 9m Create Account. Straightness, Flatness, Circularity, Cylindricity, Line profile, Surface profile, Perpendicularity, Angularity Parallelism, True position, and Concentricity callouts can be added to various created entities and shown in the report. It essentially means the same thing — the total variation from highest to lowest gage point. This is reasonable from ISO point of view (because ISO concentricity is just a special case of ISO position), but in ASME world concencentricity is something totally different than position, and in this application it would not be proper choice. The geometric dimensioning and tolerancing (GD&T) standards in ASME Y14. Dont take it personal, we all screw up big at times, My favorite screw up is to be . To examine the differences in these concepts it is helpful to first review the Geometric Dimensioning and Tolerancing hierarchy of SLOF - Size, Location, Orientation, and Form. Both symbols focus on the theoretical center datum being constrained within a specific limit to ensure that the entire structure is uniform. 5 -2018 Paragraph 4. These measurements would then need to be compared to. 4 and it would be about a close as one will get but not perfect. It is often used in lieu of concentricity and symmetry which also belong to GD&T location controls group. Your challenge is to create a backbore operation in this part that has a tight concentricity callout. Sometimes called roundness, circularity is a 2-Dimensional tolerance that controls the. The top section is the size and shape of the target area. We can control and measure the location of different. Datum A is a dashed line through the axis of the ring. 5 text for mention of the word “concentricity. Luckily, we know someone. Transforming CMM Metrology with PC-DMIS Pro, CAD and CAD++ software. In metrology and the fields that it serves (such as manufacturing, machining, and engineering ), total indicator reading ( TIR ), also known by the newer name full indicator movement ( FIM ), is the difference between the maximum and minimum measurements, that is, readings of an indicator, on the planar, cylindrical, or. Measurement setup requires at least two indicators at 180 degree to each other, rotating the part and noting the readings of both indicators at each "clock" position, after that doing some math, as to determine the cloud of the median point and so forth. For more ALT codes for various signs and symbols, see ALT Codes for Miscellaneous Symbols. ID. Drafting: What's the proper way to specify concentricity? This is more of a drafting question than an SE specific question, but hopefully one of you can help. You really don't even need a tapered shoulder. Datum B is also a plane. Transforming CMM Metrology with PC-DMIS Pro, CAD and CAD++ software. Within the GDT panel: Oct 25, 2011. I am measuring a cylinder. Straightness can control two very different types of functions. 5 is clear on this. 001 between the same two surfaces would allow only . It’s a simple issue of uniformity. and the most common example is comparing the ID and OD relative to each other on a hollow shaft or tube. Any shoulder angle (even 90 degrees) cut true on both the male and female threads should align your. Transforming CMM Metrology with PC-DMIS Pro, CAD and CAD++ software. Keep in mind though that Y14. This scan must then be analyzed to determine the central axis points at each location along the cylinder, forming the true part axis. You can attach a datum feature symbol to the following items: In a part or assembly, on a planar model surface or on a reference plane. The CMM operators decided they would look at the check with a concentricity function. 1 in this perpendicularity. Cylindricity is a 3-Dimensional tolerance that controls the overall form of a cylindrical feature to ensure that it is round enough and straight enough along its axis. It's also not in the newest edition. From Old School conventional guys, to CNC Programmers, to the…When you call out parallelism, flatness is implied. 05mm and we were getting numbers around. . Despite the difference in name, both do broadly the same. In geometric dimensioning and tolerancing (GD&T), a unique set of GD&T symbols are used to define the relationships between part features and measurement references. The first three characteristics (deviations) may be toleranced either together (in common) by the profile tolerance of the cone ( t in Fig. You will be taken to the agent interface. The general rule of thumb is not to use threads for alignment. Specifically, concentricity should generally not be used except under extraordiary circumstance. Concentricity treats the mating surfaces as ideal circles, which is ideal for alignment. It is common to encounter designs where runout, roundness and concentricity might all apply. First, the journal would be measured to find out how much runout it had. Circularity vs concentricity. True position finds the centroid of the surfaces. is a 2D measurement that can be either be taken in the axial direction or in the radial direction. Concentricity: The rings on a bullseye are concentric, just as the wheels on your car are concentric to the axle. Concentricity is a mostly obsolete/redundant callout, but that is essentially what this is. Fluent with axial and radial stack ups as well as… In this thread, for example, you want to apply concentricity callout to the hole. Parallelism b. 02. That is exactly how it appears on the drawing. Concentricity. The part kept wanting to flex in the 4 jaw. 09-16-2008, 09:28 AM. What I'm finding is that making the cylinder the datum I get bad results for the runout or concentricity. GD&T Professional Geometric Learning Systems . From the ribbon select Concentricity. The inspector must take a number of two point measurements (theoretically an infinite amount of them) as shown below. List of principal searches undertaken by users to access our and most widely used expressions with the word «concentricity». I just wanted to see how you might handle this concentricity callout in this cavity: Pic11. I know concentricity is obsolete, but I'm curious how you guys would handle this. I know concentricity is obsolete, but I'm curious how you guys would handle this. Creating the GDT Call-out. Figure 26. 75 mm from the face of the shoulder. Concentricity would require side B to be measured in all dimensions several times to obtain a full dimensional scan of the surface of the reference feature. No axis can be perfectly straight. ground on the outside diameter (OD) and also ground on the inside diameter (ID) the difference from dead zero on an indicator is your concentricity deviation from perfect. A geometric tolerance symbol frame. 001 also limits the roundness of each feature, and their shared axis of rotation. We make 'encoder disks' which are disks that have a pattern on them that typically have to be held with a tight tolerance against the ID as204K subscribers in the Machinists community. If even one of the discs deviates too much in size or roundness compared to the others or it. John Riggins. png. In terms of programming (code off the top of my head):We would like to show you a description here but the site won’t allow us. Two gears with the concentricity callout. It can be out of round by more than the concentricity callout, but still pass if the out or roundness is symmetrical. use cylindricity and concentricity items from the dimensions toolbar to report per the drawing. Concentricity and symmetry are also types of location tolerances. As shown in Fig. Here is something else one could do. pdf from MOW 217 at University of Pretoria. V-blocks are not the correct datum simulator. axis and surface d. This is reasonable from ISO point of view (because ISO concentricity is just a special case of ISO position), but in ASME world concencentricity is something totally different than position, and in this application it would not be proper choice. For example, injection-molded medical equipment uses a drastically different set of controls than a high RPM automotive component. The shoulder is the ledge between threads and shaft. Fundamentals of GD&T Part II. In GD&T, concentricity is a complex tolerance used to establish a tolerance zone for the median points of a cylindrical or spherical part feature . This callout sets a standard on how straight a feature must be along its length. First of all, it seems to be one that goes back a few decades (because the datum reference is listed before the tolerance value), but the problem is mainly in the mixing of TIR with the concept of concentricity. Free State vs Constrained. True position finds the centroid of the surfaces. Circularity is a GD&T tolerance the can can applied to parts features to assure conformity to design standards. As I posted today in thread entitled "True position callout" there are at least two additional methods of assigning two or more features coaxial: 1. As shown from the table, the Straig htness Tolerance remains the same regardless the change on the FOS of the diameter . That said, if balance matters that much, you'll likely have it tightly controlled with runout anyway, and then balance it after machining. Please, analyse my method to measure the concentricity too, and tell me your opinion. 001. Select the GDT tab. Look at the most powerful GDT callouts available: Composite Profile and. Measurement setup requires at least two indicators at 180 degree to each other, rotating the part and noting the readings of both indicators at each "clock" position, after that doing some math, as to determine the cloud of the median point and so forth. ) has to "wrap" around the entire. FIG 5-50 OR SECTION 5. 5M-1994, 5. 5. RE: Meaning of T on Concentricity KENAT (Mechanical) 2 Feb 12 13:21. I'm inspecting a manifold with a custom bore. This passage reads “However, two past practices, use of concentricity and use of symmetry symbols, are no longer supported. Determine if separate gaging should be specified for some position and/or profile specifications. Is there a way to set default file types for images and CAD files? I primarily use . (Note that symmetry and concentricity symbols are available in SolidWorks, but are no. 004 smaller than stock size. Any application where the median points of a feature need to be controlled relative to a datum would require cylindricity. Now, don’t get me wrong; it is a different 20% for each company or industry. #2. In contrast, the runout considers how the target deviates from the dimensions of a circle when it is perfectly positioned on the rotation axis. From the ribbon select Position. Drawing callout. The intended meaning of the . A requirement that the centerline or axis of two features are located together. The following formula is used to calculate the concentricity: C = Wmin/Wmax * 100%. Search. Next, the roller body would be rotated in the same setup and have its runout measured in several locations. It is recommended to use a measurement device such as a coordinate measuring machine (CMM), optical comparator, or laser scanner to measure the position of the axis or center plane of the cylindrical or spherical feature relative to the datum axis or center plane. In the case of axis parallelism, the zone’s shape is cylindrical which is represented by a diameter symbol in this block. Measure around the specified circumference. Concentricity, and Symmetry, are RFS. Specified measurement position. Concentricity Measurement. Concentricity is generally reserved for high-precision parts, and only when there is a need to control median points. A concentricity tolerance specifies a cylindrical tolerance zone whose axis coincides with a datum axis and within which all cross-sectional axes of the feature being controlled. • For workpieces with high concentricity callout • For radial readjustment of workpieces with big changes in weight during machining • To apply additional grip force to the workpiece by the adjustment screws • Readjustment of the centerline of the workpiece in process Technical features • Integrated fi ne adjustment to center the. Circularity vs concentricity. As I stated earlier, the method you're referring to is most definitely wrong--it describes, at least partially, how to do a true position calculation. The Concentricity callout points the arrow to the feature while the datum is the axis. 5? As I understand the standard, it is looking for all of the median points of diametrically-opposed elements of the feature. We would like to show you a description here but the site won’t allow us. Description: Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature, to a datum axis. Select “Geometric Tolerance” and the user interface window will pop up that allows us to input the GD&T controls.