gd&t - toronto mechanical design, part and assembly drawings, toronto cad drawings

8/10/2019 GD&T - Toronto Mechanical Design, Part and Assembly Drawings, Toronto CAD Drawings

1/12

9/9/2014 GD&T - Toronto Mechanical Desig n, Part and Assembly drawing s, Toronto CAD drawing s

http://www.torontodrawings.com/9.html

Fasteners

Thread

Carbon_Steels

Stainless_Steels

More About Steels

Steel Products

GD&T

Welding

Machine Shop

Plastics

Professional drawings; flexible hours; competitive cost.

Geometric Dimensioning and Tolerancing

1. Datum, Datun planes, Datum features and Datum targets.

A datum is a theoretical exact point, axis or plane from which the location or geometric

characteristic of a part feature are established. It's a s tarting point or origin.

A datum established by an actual physical part feature called a datum feature. A datum featuretypically has an important functional relationship to the part feature being specified. On a

drawing, it's identified by a special datum feature symbol.

Example: A flat surface may be used to establish a datum plane. A cylindrical feature, such as a

shaft, may be used to establish a datum axis. A slot may be used to establish a datum center

plane.

By definition, a datum is theoretically exact or perfect. However, the actual part feature used to

establish the datum is not perfect. Therefore, the datum is simulated through contact with

precision manufacturing or inspection equipment. This provides a more accurate stating point

from which to measure.

(Refer to here for more)

2. Definations:

Basic Dimension- A basic dimension is a theoretically exact value us ed to describe the exactsize, profile, orientation or location of a feature. A basic dimens ion should always as sociated

with a feature control frame or datum target. Block tolerance does not apply and the applicable

tolerance will be given within the feature control frame. Basic dimensions are enclosed within a

box.

Use bas ic dimens ioning to locate features (e.g. holes), use tolerances on the size of features

(e.g. holes ).

Form Tolerances

3. Straightness

The feature control frame shows that each line element of the surface of the pin m ust be s traight

within 0.05 mm.

Home Project Design Rate Contact Us Links_Ref
http://www.torontodrawings.com/Project.htmlhttp://www.torontodrawings.com/Rate.htmlhttp://www.torontodrawings.com/Contact_us.htmlhttp://www.torontodrawings.com/Links_Ref.htmlhttp://www.torontodrawings.com/index.htmlhttp://www.torontodrawings.com/index.htmlhttp://www.torontodrawings.com/index.htmlhttp://www.torontodrawings.com/Links_Ref.htmlhttp://www.torontodrawings.com/Contact_us.htmlhttp://www.torontodrawings.com/Rate.htmlhttp://www.torontodrawings.com/Project.htmlhttp://www.torontodrawings.com/index.htmlhttp://www.torontodrawings.com/index.htmlhttp://www.torontodrawings.com/Plastics.htmlhttp://www.torontodrawings.com/MachineShop.htmlhttp://www.torontodrawings.com/10.htmlhttp://www.torontodrawings.com/9.htmlhttp://www.torontodrawings.com/13.htmlhttp://www.torontodrawings.com/12.htmlhttp://www.torontodrawings.com/11.htmlhttp://www.torontodrawings.com/8.htmlhttp://www.torontodrawings.com/Thread.htmlhttp://www.torontodrawings.com/Fasteners.html


2/12


http://www.torontodrawings.com/9.html 2

This means that each lengthwise line element of the surface of the pin mus t lie between two

parallel lines that are 0.05 mm apart. This applies to any lengthwise line element of the surface.

However, the tolerance zone (0.05 mm) need not be parallel to the axis of the pin.

There are two kinds of straightness tolerance - (1) Straightness of an axis or center plane and

(2) surface s traightness. The type of s traightness is determined by the placement of the feature

control frame.

When the feature control frame is next to the s ize dimension, it is controlling the axis or center

plane.

When the feature control frame is on a leader line pointing to a surface, the straightness is

applied to line elem ents in the surface.

Another example:


3/12



The above means :

The derived median l ine of the feature actual local sizes must lie within a cylindrical tolerance

zone of 0.04 diameter at MMC. As each actual local size departs from MMC, an increase in the

local diameter of the tolerance cylinder is allowed which is equal to the amount of such

departure. Each circular element of the surface mus t be within the specified limit of s ize.

(See more details here)

The straightness symb ol is sometimes used to ensure mating features (e.g. a dowel or other

press-fit assemb ly) will create a tight fit without the use of fasteners.

4. Flatness

The flatness control means that the surface must lie between two parallel planes that are 0.006"

apart. The part thickness (1.000-1.020") must als o be within the Envelope of Perfect Form

unless otherwise specified on the drawing. In other words, the feature mus t fall within the size

tolerance, e.g. at MMC (Maximum Material Condition) of 1.020", the surface must be perfectly flat.

When verifying flatness, the feature of size is first measured to verify that it falls within the limits

of s ize (1.000-1.020).

Please note: Flatness applies to the entire surface while straightness applies to a single linear

element.


4/12



5. Circularity

Each circular element of the surface in any plane perpendicular to a common axis mus t be

within the specified tolerance of s ize and mus t lie between two concentric circle (one having a

radius .0.10 larger than the other).

The part cannot extend beyond its envelope of perfect form. At the MMC (21 mm diameter), the

part mus t be perfectly round and straight.

6. Cylindricity

Orientation Tolerances

7. Parallelism

Example 1.

Example 2.


5/12



Means:

Example 3.

Means:

Example 4.

8. Perpendicular

Perpendicularity of a flat surface to a datum Plane:


6/12



Perpendicularity of a cylindrical s urface to a datum Plane:


7/12



At MMC, the feature axis must lie within a cylindrical zone of 0.3 diameter which is perpendicular

to and projects from datum plane A for the 14mm specified height. The feature axis m ust be

within the specified tolerance of location over the projected height.

The following print shows a part that specify the 1.000-inch pin perpendicular to the top surface

of the part within a tolerance of .040 at MMC. A gage is also shown to inspect the part.

9. Angularity

Profile Tolerances

10. Profile of a Line

A two-dimens ional tolerance zone that controls individual l ine elements of a feature or surface.

Profile of a line is us ually applied to parts with varying cross -sections, or to specific cross

sections critical to a part's function. Examples of parts where profile of a line could be applied

include aircraft wings and housings used to seal out dust or water.


8/12



11. Profile of a Surface

A geom etric tolerance that controls how much a surface can deviate from the true profile. Profile

is a three-dimensional tolerance that applies in all directions regardles s of the drawing view

where the tolerance is specified. It is usually used on parts wi th complex outer shape and aconstant cross-section like extrusions.

Means:

The top surface of the part must lie within

a profile tolerance zone of 1.5 mm on

each side of the basic profile. This

tolerance is applied to the bas ic print

dimension of 30 mm measured from

datum plane "A

(Refer to here for more details )


9/12



The entire surface of the die cavity mus t lie within a profile tolerance zone of 0.015 outside the

true profile.

The entire surface of the punch must lie within a profile tolerance zone of 0.015 inside the true

profile.

Note that if the leader from a profile feature control frame points directly to the true profile, the

tolerance specified is equally dispos ed about the true profile . If the leader from a profile

tolerance points directly to a segment of a phantom line extending, outside or ins ide, parallel to

the profile, then all the tolerance is outside or inside the true profile.

Note that if the design requires a smaller radius than the radius allowed by the profile tolerance,

a local note such as , ALL CORNERS R.015 MAX, or R.015 MAX is directed to the radius with a

leader.

12. Circular Runout

Runout is a measure of how perfectly a circular part rotates about its axis.


10/12



Circular runout applies independently to each circular element on the surface of a part either

constructed around a datum axis (left image above) or perpendicular to a datum axis (right

image above) as the part is rotated 360 about its datum axis.

Runout is measured as the FULL INDICATOR MOVEMENT (FIM). For example, if the needle on

the dial moves from -1 to +1, the FIM is 2 mm.

The boxed symbols can be read "each circular element of this surface mus t have full indicator

movement (FIM) of less than 0.05 relative to datum A".

The above image shows a sample measurement taken at one cross section, but multiple

meas urements are required to verify runout. Note that the indicator is applied perpendicular to

the meas ured surface, and that this tolerance controls only individual circular elements and not

the whole surface simultaneous ly.

Where applied to surfaces of revolution, circular runout controls a combination of variations in

circulari ty and coaxiality.

Circular runout example:


11/12


12/12


Total runout is sim ilar to circular runout with the exception that the dial indicator is moved back

and forth over the entire controlled s urface while the part is rotated. The full indicator movement

on the dial indicator over the entire surface of the controlled feature cannot be more than 0.02

mm. This als o controls cumulative variations of straightness , roundness and taper of the

surface.

Where applied to surfaces constructed around a datum axis, total runout controls a combination

of surface variations such as circularity, straightness, coaxiality, angularity, taper, and profile.

Where applied to surfaces at a 90 angle to the datum axis, total runout controls a combination

of variations ofwobble, flatness and perpendicularity to the datum axis.

14. Position

15. Concentricity

16. Symmetry

Circular runout inspection:

Torontodrawings.com

gd&t - toronto mechanical design, part and assembly drawings, toronto cad drawings

Documents