While the basics of position are covered in a standard Geometric Dimensioning & Tolerancing (GD&T) course, and sometimes a lone example of composite position is given, those discussions often overlook the variations allowed that enable more accurate control based on part function. This advanced web.
|
GD&T Symbol:
Relative to Datum: Yes
MMC or LMC applicable: Yes (Uncommon)
Drawing Callout:
Description:
Angularity is the symbol that describes the specific orientation of one feature to another at a referenced angle. It can reference a 2D line referenced to another 2D element, but more commonly it relates the orientation of one surface plane relative to another datum plane in a 3-Dimensional tolerance zone. The tolerance does not directly control the angle variation and should not be confused with an angular dimension tolerance such as ± 5°. In fact the angle for now becomes a Basic Dimension, since it is controlled by your geometric tolerance. The tolerance indirectly controls the angle by controlling where the surface can lie based on the datum. See the tolerance zone below for more details.Maximum material condition or axis control can also be called out for angularity although the use in design and fabrication is very uncommon since gauging a hole or pin at an angle is difficult. When angularity is called out on an axis, the tolerance zone now becomes a cylinder around the referenced axis at an angle to the datum. The page on Perpendicularity goes into this type of reference in further detail since it is more common with perpendicularity.GD&T Tolerance Zone:
Two parallel planes or lines which are oriented at the specified angle in relation to a datum. All points on the referenced surface must fall into this tolerance zone.Angularity does not directly control the angle of the referenced surface; it controls the envelope (like flatness) that the entire surface can lie.
Gauging / Measurement:
Angularity is measured by constraining a part, usually with a sine bar, tilted to the reference angle, so that the reference surface is now parallel to the granite slab. By setting the part at an angle the flatness can now be measured across the now horizontal reference surface. The entire variation must not fall outside the tolerance zone.Relation to Other GD&T Symbols:
Perpendicularity and Parallelism are actually refined forms of Angularity. Perpendicularity describes angularity at 90° and parallelism describes it at 0°. All of these are profiles of orientation and are used in the exact same way. They also can be used with control of an axis under maximum material condition, although perpendicularity is usually the only one you will ever see with this callout.Orientation GD&T Symbols are also closely related to flatness when the surfaces are is flat planes. When you call out any of the orientation symbols, flatness is implied (you are measuring a surface variation between two parallel planes = Flatness) However the biggest difference is that orientation callouts are measured with respect to a datum, where flatness is not.When Used:
Angularity helps control any feature that is at an angle to another datum surface. Anytime you have a critical feature which mates with other part at an angle, angularity can be used to help control the angle and flatness of the mating surfaces. Many stamped parts that have bent features use angularity to ensure that the 3D surface formed by the stamping operation that is formed always is controlled and encased in a tolerance zone.Example:
If you have a stamped part that had to hook into another part at an angle of 30 degrees, you would want to call out angularity on the “bent” feature to ensure that it is always at its proper orientation. If you did not use angularity you would have to both tighten the angle tolerance of the part and the thickness tolerance of the referenced surface. Angularity example 1: Tightening the angle and/or the thickness are required if angularity is not called out.Angularity example 2: A simple call to angularity now ensures that the stamped surface now has both proper angle and flatness. The angle must be a basic dimension, but now allows your part thickness to open up more. (Note this drawing is unconstrained and would need additional size dimensions to be accurate.)Remember – You are not controlling the angle with angularity – you are controlling the surface to fall within the specified dimensional tolerance in millimeters!Final Notes to Remember:
Datum Relationship:
Since all of the orientation symbols (Angularity, Perpendicularity, and Parallelism) are referenced to a datum – essentially the tolerance is not measuring a specific surface or feature on its own. You are measuring the relationship of one feature or surface with respect to another feature. If one feature is out – both surfaces could be incorrect.Maximum Material Condition:
Maximum material condition can also be used in a similar method of perpendicularity. Although MMC is usually for pins or holes which need to be perpendicular to a reference surface, so it is not commonly used on angularity. See Perpendicularity for more details about Gauging and Calling out MMC on an orientation symbol.Dimensional Angularity:
As stated before: 2-Dimensional references can also be used with angularity to ensure that an angle is met around a round or complex feature. If you wanted to specify the angle of a cone for example, the angularity would apply to each line element along that cone referenced to the bottom of the cone.GDandT Basics
StraightnessProfile of a LineRelated Posts
True Position
LinkEnlarge
Circularity
LinkEnlarge
Parallelism
LinkEnlarge
Cylindricity
LinkEnlarge
Profile of a Surface
LinkEnlarge
Runout
LinkEnlarge
Concentricity
LinkEnlarge
Perpendicularity
LinkEnlarge
Total Runout
LinkEnlarge
Profile of a Line
LinkEnlarge
Straightness
![Measurements Measurements](http://www.builditsoftware.com/wp-content/uploads/Pin_LMC_MMC_clean.gif)
LinkEnlarge
Symmetry
LinkEnlarge
Flatness
LinkEnlarge
PreviousNext40 Comments
Andrea Horansays: April 24, 2018 at 9:26 amMatt, I have an older drawing that has a dimension of 1 degree-3 minutes. The Feature Control Frame tolerance for angularity is +/- 2 degrees. Imagine you are holding a crochet hook parallel to the floor with the “hook” pointing down. The angular tolerance is from the top surface of the hook, which would be a datum on a more recent drawing.
At what distance would the parallel planes be on either side of the surface to be measured? 2[sin(2 degrees)]? Or sin(2 degrees)? With the part’s being only 11 inches long, I don’t believe it makes sense for the hook portion to be able to vary within a tolerance of up to 4 inches, or even 2 inches, so I’m quite lost.
Thank you for clarifying.
Andrea
ReplyMatt Derrsays: April 29, 2018 at 12:13 pmAndrea –
The tolerance zone for the angularity zone is a linear dimension and not an angle. So whatever your value is, it’s given in inches or mm. I’m guessing by your post that it’s 2 mm. Also, the tolerance value given in the feature control is a total value and not a +/- value. The tolerance zone is two parallel planes separated by a distance as given in the feature control frame. The tolerance zone is oriented to your datum structure by a basic angle that has no tolerance. The entirety of the surface must be located within this zone for the part to be considered acceptable.
If you have any additional questions you’d like answered after I’ve hopefully clarified a few things, please feel free to ask.
Cheers,
Matt
ReplyJAMIE BARLOWsays: April 30, 2018 at 7:51 amMatt
IVE BEEN HEARING THIS LATELY, AND HAVE NEVER HEARD IT BEFORE. ” FOR EVERY 1° ANGLE DIFFERNCE, (OFF KILTER) THEIR IS A .030 DISCREPENCY IN A HOLE DIMENSION CALLOUT.
IS THEIR A FORMULA THAT STATES THIS?
ILL ASSUME THIS MIGHT BE TRUE FOR A GREATER DISTANCE BUT TRYING TO VERIFY A TRUE POSITION TOLERANCE OF A HOLE IN A FORMED PART. THE ANGLE SEEMS TO ONLY AFFECT ONE DATUM, THUS CONFUSING THE VALIDITY OF THIS STATEMENT? ANY HELP, THANK YOU!
ReplyMatt Derrsays: May 8, 2018 at 10:49 pmIS THEIR A FORMULA THAT STATES THIS?
ILL ASSUME THIS MIGHT BE TRUE FOR A GREATER DISTANCE BUT TRYING TO VERIFY A TRUE POSITION TOLERANCE OF A HOLE IN A FORMED PART. THE ANGLE SEEMS TO ONLY AFFECT ONE DATUM, THUS CONFUSING THE VALIDITY OF THIS STATEMENT? ANY HELP, THANK YOU!
Jamie –
That is somewhat odd, I’ve never heard of that rule of thumb before. I have a hard time taking it at face value as it’s totally dependent on the thickness of the material you are dealing with. The axis of your hole moves a distance equal to [(h/2) * tan (alpha)] where h is the thickness of the material and alpha is the tilt angle.
I hope this helps.
Cheers,
Matt
Replyumitsays: May 10, 2018 at 9:01 amMatt
How can I calculate the angle between two points with tolerances?
Sample; The tolerance of point A is +/- 1.5 and the tolerance of point B is +/- 1.1. According to these tolerances, what is the angular value of point B according to the point if I do not draw a line between two points?
ReplyBarathsays: May 11, 2018 at 7:01 amSample; The tolerance of point A is +/- 1.5 and the tolerance of point B is +/- 1.1. According to these tolerances, what is the angular value of point B according to the point if I do not draw a line between two points?
Objective of angularity inspection ?
ReplyMatt Derrsays: May 13, 2018 at 1:29 pmBarath –
I’m talking about surfaces for this example. Angularity is essentially an oriented flatness control. The tolerance zone is two parallel planes oriented by some basic angle relative to an identified datum plane. The entirety of the controlled surface must lie within the tolerance zone to be considered in specification.
I hope this helps clarify things for you. Come back any time with additional questions.
Cheers,
Matt
ReplyLoren VanHornsays: June 27, 2018 at 10:19 amMatt
I have an angle dimension that is listed as a basic dimension, the only control frame is for positional tolerance, how do i calculate or interrupt this?
ReplyMatt Derrsays: August 5, 2018 at 6:40 pmLoren –
I’m guessing that your drawing is trying to locate the center of a hole relative to your datum structure. Do you have any other basic dimensions on your drawing? Look at your drawing and see where your datums all intersect. Make a mark in red pen at that point. Your hole must be oriented and located relative to that point through a combination of basic dimensions and angles. Keep in mind that the term basic means theoretically exact. I say point, but in reality the datums are almost certainly intersecting in a single line.
I hope this clears things up for you. If not, please come back and ask more questions.
Cheers,
Matt
Reply« Older CommentsMatt