Geometric Tolerances & Dimension

Geometric Tolerances & Dimension is the idiom used by Mechanical Engineer to commune information & Design & Drawing intent to the mechanized & inspection organizations. Appropriate use of this idiom will insure that product will function appropriately & will be manufactured at the lowest cost possible. Mechanical Engineer, Production Engineer & inspection & Quality control personnel must understand the symbols & the idiom to perform their duties. Designer must also be fluent enough to translate requirement & intent to instruction that manufacturing & inspection technicians can understand precisely & without ambiguities.

CIM Environment

Hole Callouts & To draw a countersunk hole in cad

There are four industrialized processes that produce hole shape characteristics that are used so often that they are defined using standardized drawing callouts: Ream, Counter bore, countersink and spot face.
Reaming is a procedure that smooths out the inside of a drilled hole, holes created using twist drills having spiral shaped machine mark on their surfaces. Reaming is used to remove the spiral machine marks & to increase the roundness of the hole. Ream callout generally include a much tighter tolerance than do drill diameter callouts.
A counter bore consists of holes drilled along the same centreline, counter bore are used to allow fasteners or other objects to be recessed, thus keeping the top surface uniform in height.
A counter bore drawing callout specifies the diameter of the small hole, the diameter of the large hole, & the depth of the large hole.
The information is given in this sequence because it is also the sequence of manufacture. Note that the hidden lines used in the front view of the counter bored hole clearly show the intersection between the two holes.
A countersink is a cone-shaped hole used primarily for flat –head fasteners. The drawing callout specifies the diameter of the hole, the included angle of the countersinks & the diameter of the countersinks as measured on the surface of the object. Almost all countersinks are 82° but some are drawn at 45°.
A spotface is a very shallow counterbored hole generally used on cast surfaces.cast surfaces is more porous than machine surfaces. Rather than machine an entire surface flat, it is cheaper to manufacture a spotface because only a small portion of the surface is machined. Spotfaces are usually used for bearing surfaces of fasteners.

A spotface callout defines the diameter of the hole & the diameter of the spotface. A depth need not be given, when machining was done mostly by hand, the machinist would make the spotface just deep enough to produce a shiny surface (most cast surfaces are more gray in colour) so no depth was needed. Automated machines require a spotface depth specification. Usually the depth is very shallow.

 To draw a countersunk hole in cad

1.     Draw a circle 10 mm diameter hole in the top view and project the hole’s diameter into the front view.

2.     Draw another concentric circle 20 mm diameter hole in the top view and project its diameter into the front view. In the front view draw 45° lines from the intersection of the 20 mm diameter circle hole & the top surface of the front view so that the lines intersect the 10 mm diameter circle hole’s projection lines. Use OSNAP (Shift + mouse right click), intersection to ensure accuracy.

3.     Draw a horizontal line between the intersection created as per above mention, once again use osnap intersection.

4.     Trim & erase the excess lines.

Section Views

The modus operandi called section views is used to advance the prophecy of innovative designs, elucidate multiple view drawings and smooth the progress of the dimensioning of drawings. For mechanical drawings section views are used to divulge internal description of an object that is not easily represented using concealed lines.
Sectional drawings are multiple view methodological drawings that contain unique views of a part or parts, a view that divulge internal description. Conventional sections views are based on the use of a pretend cutting plane that cuts through the object to divulge internal description.

A full section view is made by passing a pretend cutting plane entirely through an entity. Pretend cutting plane ephemeral entirely through an entity and half of it being isolated. In a multiple view drawing, a full section view is placed in the same position that an unsectioned view would usually dwell in; that is, a front section view would substitute the conventional front view.

Half sections are created by ephemeral an pretend cutting plane intermediate through an entity and one quarter of it is isolated. Concealed lines are omitted on both halves of the section view. Peripheral features of the part are drawn on the unsectioned half of the view. A centre line, not an object line, is used to separate the sectioned half from the unsectioned half of the view. Half section views are most often used on parts that are symmetrical.

A broken-out section is used to show core description of a ingredient by breaking away some of the entity. A broken-out section is used instead of a half or full section view to save time. A break line separates the sectioned from un-sectioned half of the view. A break line is drawn free-hand to represent the jagged edge of the break. No cutting plane line is drawn with a broken-out section view.

A revolved section is made by gyrating to the cross-section view of the part about an axis of rebellion and placing the section view on the ingredient. The cross section created at the position that the cutting plane passed is then revolved 90 degrees and drawn on the view. Visible lines adjacent to the revolved view can either be drawn or broken out using conventional breaks. It is used to depict the section of an elongated entity without the need to illustrate the entire sectional view.

Removed sections are used to show the contours of problematical shapes such as blades for jet engines. Removed sections are made in a manner analogous to revolved sections, by passing an pretend cutting plane perpendicular to a part then revolving the cross section 90 degrees. However, the cross section is then drawn adjacent to the orthographic view, not on it. If a number of removed sections are done on a part, cutting plane lines may be drawn with labels to elucidate the position from which each section is taken. Whenever possible, a removed section should be on the same sheet as the part it represents, and it should be clearly pigeonholed.

An offset section has its cutting plane bent at 90 degree angles to pass through significant characteristics. Offset sections are used for versatile parts that have a number of significant characteristics that cannot be sectioned using a straight cutting plane. The significant internal features of an entity are not lying on a single plane, a full section may not be able to show all the details. Offset section is a technique whereby the cutting plane offsets to pass through various features that would otherwise be missed by a full section. Thick lines should be used at the change of direction of the cutting plane.

Aligned sections are special types of orthographic drawings used to revolve or align special features of parts to clarify or make them easier to represent in section. Normally the alignment is along a horizontal or vertical center line and always less than 90 degrees.

Elucidation of Computer Aided Design

Computer Aided Design is assistance of computer in engineering processes such as creation,modifications & optimization,analysis.

Computer Aided Design involves creating computer models defined by geometrical parameters which can be readily altered by changing relevant parameters. CAD systems enable designers to view objects under a wide variety of representations and to test these objects by simulating real-world conditions.

It is an integration of Mechanical and Computer technology to aid in the design process like Drafting, Die Design, Tool Design, Sheet metal,Modeling, Assembly,  analysis of products.

It is both a visual and fast process which is used by Engineers in the Mechanical, Automobile, Production, Plastic, Aeronautics field to design and develop the entire product on the computer before realy producing it.

CAD is mainly used for detailed engineering of 3D models and 2D drawings of physical components, but it is also used throughout the engineering process from conceptual design and layout of products, through strength and dynamic analysis of assemblies to definition of manufacturing methods of components.

The designed product on the computer can be tested, modified and finalize for real production.

Primitive Commands

array	Ø  To use a Rectangular array option Ø   To use a Polar array option
Rotate	Ø  To rotate an object in clock wise direction or anti clockwise direction
Trim	Ø  To use  the trim commands
Extend	Ø  To use the extend ( project/edge/undo)
Break	Ø  To use the break at a point command Ø   to use the break command Ø  to use the First-point option
Chamfer	Ø  To create a chamfer (polyline/distance/angle/trim/method)
Fillet	Ø  To draw a fillet (polyline/radius/trim)
Osnap	Ø  To access the object Snap toolbar Ø  To turn Osnap on, To change the size of the Osnap cursor box Ø   Osnap –End point ( to snap to the endpoint of a line) Ø   Osnap –snap from (to move a line, To change the angle & the length of a line) Ø  To apply the snap from option to a circle, Osnap – Midpoint ( to draw a circle about the midpoint of a line) Ø   Osnap –Intersection (To use the osnap ontersection command to define an ellipse) Ø  Osnap-apparent Intersection (To draw a circle centered about an apparent intersection) Ø  Osnap –center ( to draw a line to the center point of a circle) Ø  Osnap-Quadrant ( To draw a line to one of a circle’s quadrant point) Ø  Osnap-perpendicular ( to draw  a line perpendicular to a line) Ø  Osnap-Tangent ( to draw a line tangent to a circle) Ø  Osnap-nearest ( To draw a line from a point to the nearest selected point on an existing line)
Grips	Ø  To turn the grip function off Ø  to access the grips dialog box,
Blocks insert	Ø  To create a block Ø  To insert a block Ø  To change the scale of a block Ø  To explode a block Ø  To insert blocks at different angles
Write block	Ø  To create a wblock Ø  To verify that a wblock has been created Ø  To insert a wblock into a drawing.
layers	Ø  To create new layers Ø  To change the color & linetype of a layer Ø  To draw in different layers,To change layer Ø  To change the scale of a linetypes Ø  To use the global line type scale factor,
Match properties	Ø  To use the match properties tool Ø   To turn layers off
Attributes	Ø  To add an attribute to a block Ø  To create a new block that includes attributes Ø  To insert an existing block with attributes Ø  To edit an existing attribute Ø  To use the edit global command Ø  Title blocks with attributes,

array	Ø  To use a Rectangular array option Ø   To use a Polar array option
Rotate	Ø  To rotate an object in clock wise direction or anti clockwise direction
Trim	Ø  To use  the trim commands
Extend	Ø  To use the extend ( project/edge/undo)
Break	Ø  To use the break at a point command Ø   to use the break command Ø  to use the First-point option
Chamfer	Ø  To create a chamfer (polyline/distance/angle/trim/method)
Fillet	Ø  To draw a fillet (polyline/radius/trim)
Osnap	Ø  To access the object Snap toolbar Ø  To turn Osnap on, To change the size of the Osnap cursor box Ø   Osnap –End point ( to snap to the endpoint of a line) Ø   Osnap –snap from (to move a line, To change the angle & the length of a line) Ø  To apply the snap from option to a circle, Osnap – Midpoint ( to draw a circle about the midpoint of a line) Ø   Osnap –Intersection (To use the osnap ontersection command to define an ellipse) Ø  Osnap-apparent Intersection (To draw a circle centered about an apparent intersection) Ø  Osnap –center ( to draw a line to the center point of a circle) Ø  Osnap-Quadrant ( To draw a line to one of a circle’s quadrant point) Ø  Osnap-perpendicular ( to draw  a line perpendicular to a line) Ø  Osnap-Tangent ( to draw a line tangent to a circle) Ø  Osnap-nearest ( To draw a line from a point to the nearest selected point on an existing line)
Grips	Ø  To turn the grip function off Ø  to access the grips dialog box,
Blocks insert	Ø  To create a block Ø  To insert a block Ø  To change the scale of a block Ø  To explode a block Ø  To insert blocks at different angles
Write block	Ø  To create a wblock Ø  To verify that a wblock has been created Ø  To insert a wblock into a drawing.
layers	Ø  To create new layers Ø  To change the color & linetype of a layer Ø  To draw in different layers,To change layer Ø  To change the scale of a linetypes Ø  To use the global line type scale factor,
Match properties	Ø  To use the match properties tool Ø   To turn layers off
Attributes	Ø  To add an attribute to a block Ø  To create a new block that includes attributes Ø  To insert an existing block with attributes Ø  To edit an existing attribute Ø  To use the edit global command Ø  Title blocks with attributes,