CAD & BSI Theory. Arbroath Academy - Technology Department - National 5 Graphic Communication

Transcription

1 CAD & BSI Theory

2 These symbols are drawn from BSI. Building Drawing Symbols You may be required to use these symbols in your assignment or project, or be asked questions about them in your exam. You must use the symbols and terms specified below.

3 Technical Graphic Line Types These are the technical graphic line types that you should use in your work.

4 Dimensioning Conventions These are the conventions for technical graphic dimensioning that you should use in your work.

5 Dimensioning Conventions cont.

6 2D CAD Commands CAD Command Pan Array Grid Move Scale Mirror Rotate Group Perpendicular Zoom Trim Grid Lock Copy & Paste Constraint Extend Tangent Definition Move the viewpoint of an object without zooming in or out Repeat a graphic in a circular or square pattern Reularly spaced lines which allow accuracy when drawing To pick up a graphic and move to another position To increase or decrease the size of an item 1:2 (half), 2:1 (double) To make a symmetrical copy of a graphic Turn a gaphic by an angle, around a centre point To select and lock a group of graphics/text together When a line is at 90 degrees to each other To magnify in or out from items on a page To cut off excess lines which are not required To force your line/graphic to attach to grid points, helps with accuracy. Make identical shapes of grapihcs To force a graphic to be a certain size or angle To make your lines longer, usually until it touches another line To force a line to touch a circle or arc at one point

7 Drawing Tools Copy means to copy an object to the clipboard. Paste means to paste the contents of the clipboard onto the page. Undo means to reverse the last command Move means to move an object to a new position on the page Erase means to remove part of a drawing.

8 3D CAD Terms 3D CAD is an important aspect of Graphic Communication and you will be expected to demonstrate skill in using it throughout the Course. You will be required to answer questions about 3D CAD in your exam. You may be using terms pertaining to a specific software platform, however, you should know these generic terms for 3D CAD. These terms can be found in the Course Assessment Specifications for the Graphic Communication Courses.

9 3D CAD Terms Workplanes can be thought of as digital paper - it is here you can create your 2D sketches. Most 3D CAD programmes give you three workplanes to start with. These represent your elevation, end elevation and plan. You need to consider this when you are sketching your model You can also create your own workplanes within a drawing, it is sensible to name these workplanes. Extrude You use the Extrude command to change 2D profiles into 3D models. Material can either Be subtracted or added from the native block. Revolve To create features by revolving a profile around an axis, use the Revolve Profile command.

10 Loft Using the Loft Through Profiles command will allow you to create a continuous feature where profiles are drawn across different offset workplanes. Shell The Shell command allows user to hollow out 3D blocks leaving behind a user defined thickness of wall. This can be used to remove a face, as seen above or just used to make a shape hollow Fillet Chamfer Fillet is when you round an edge to a user defined radius Chamfer is when you cut away an edge to a user defined angle and thickness.

11 Align The Align command is used to constraint two faces, so that they are side by side. In the top left picture we see the two faces that are not aligned. After selecting Align as a constraint they are now on the same level as shown in the picture to the right. Mate The Mate command is used to constraint two faces, so that they are face to face. In the top left picture we see the two faces that are not mated. After selecting Mate as a constraint the two faces are now touching each other. This can be seen more clearly in the picture to the right.

12 The Centre Axis command is used when you are constraining two circles or a hole and a cylinder. In the top left picture we see the internal face selected of the hole and the external face of the cylinder. After selecting Centre Axis as a constraint the cylinder now sits inside the hole of the wider cylinder. The Offset command is used in conjunction with other assembly constraints. Offset is when either Align or Mate is used but a user-set distance is created between the two faces. Using the above Centre axis as an example, lets pretend we wanted to produce an exploded view. The original centre axis constraint is still in place but now we need to select the two faces we want to offset. In the second picture the top face of the bottom cylinder and the bottom ofthe smaller cylinders is selected. The resulting third picture is a Mate Offset.

13 Advantages and Disadvantages of CAD Drawings can be produced quicker and very accurately Drawings are easier to edit/change Repetitive elements, libraries of various parts can be created Convenience of use (laptop, tablet) Drawings can be easily scaled up or down Use of layers allows different parts to be drawn separately Easier to store drawings (paperless offices) Easier to send drawings to another location quickly New designs from existing designs Overall cost of hardware Overall cost of software Continual need to upgrade systems to stay competitive Risk of catching computer viruses Staff training costs System faults/crashes Data loss security An accurate 3D image can be rotated 360 degrees in any direction Allows the operator a view of an object at any angle Animation can show the designer how the parts interact and can highlight problems Simulation programs are used in speciality areas such as pilot training Computer generated imagery is used in the TV and Video industry Allows the creation of a library common parts recognised throughout an industry sector, such as BSI symbols Allows users to recognise industry standard throughout the world, such as BSI or paper size (A3,A4 etc)