Computer Aided Drafting
Thoughts for the day:
Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it.
- Sir Henry Royce, Co-Founder / Designer of Rolls-Royce Motor Co.
Scientists dream about doing great things. Engineers do them.
- James Michener, Author
Current Assignments:
Lego Project
Your job is to design and build an object made of Lego's, and then make working drawings of it. You will then disassemble the object, give your drawings to someone else in the class, and they will be required to build it exactly as you have drawn it.
PURPOSE: To develop a complete set of working drawings. A WORKING DRAWING supplies all the information necessary to manufacture a part or a complete structure. Working drawings normally include a detail drawing and an assembly drawing if the object consists of many parts.
Here is a Lego Spreadsheet to keep track of the number of pieces, colors, layers. This must be included in your final project.
SKETCH your project!! This must be completed prior to any CAD drawings!!!
SCOPE: You will produce a working drawing that will include:
- a DETAIL DRAWING. A detail drawing gives all the information needed to make each part.
- DETAIL DRAWING. Front and top view only of each type (not color) of Lego used. Each type of Lego drawn clearly and accurately in two orthographic views. USE OF LAYERS & LAYER MANAGEMENT IS ONE OF THE MOST VALUABLE SKILLS TO LEARN!!! USE THEM!!! Exterior features fully dimensioned with 4mm text. Each type of Lego named (1 x 2, 2 x 6, etc) and labeled with 8mm text. Spreadsheet on the page. Due TBA!! 10pts for meeting the deadline. 2pt deduction for EACH DAY (even Wednesday, Friday, Saturday, Sunday) late! Drawing title is "Lego Details"; Drawing # 1 of 3.
- a SUB-ASSEMBLY DRAWING. A sub-assembly is needed when many parts are put together to form the whole. For example, you wouldn't show an entire automobile, aircraft or even an engine in a single assembly. Sub-assemblies would help the builders put together the engines, drive trains, chassis, interior components, etc. In our application, we will produce each layer as a sub-assembly. This will be used to re-create your project one layer at a time!! DUE: TBA
- SUB-ASSEMBLY DRAWING : Each layer drawn clearly and accurately in top view only. Color-coded. Background layer showing. Each layer identified with 8mm Text. Dimensions Not Needed. Due TBA. 10 pts for meeting the deadline with a correct drawing. 2 pt deduction for EACH DAY the drawing is late. Drawing title is "Lego Sub-Assemblies"; Drawing # is 2 of 3.
- A drawing of the fully assembled construction is called an assembly drawing. Assembly drawings vary greatly in the amount of detail and dimensioning shown. Their special value is that they show how the parts fit together and the look of the construction as a whole.
- Assembly Drawing: Drawn clearly and accurately. Overall dimensions only; NO HIDDEN LINES ARE NECESSARY! Be sure you draw the PROJECT, not the BLOCKS!! Use of Layers is a critical skill to master! Use the appropriate layers and property controls. DUE: TBA. Drawing title is "Lego Assembly; Drawing # is 3 of 3.
Design Parameters: The design must…
- be built of Lego's provided my Mr. Seibel.
- have between 80 and 100 pieces.
- have at least 4 colors of Lego's, with the minimum number of any one color being 10 %.
- have at least 4 types of Lego's.
- have from 4 to 6 layers.
- not be a solid mass.
Multi-View & Dimensioning Practice:
Dimensioning Guidelines
General Rules for Dimensioning (See example below!)
- Dimensions should NEVER be duplicated, or the same information be given in two different ways.
- No unnecessary dimensions should be used - only those needed to produce or inspect the part.
- Dimensions should be placed at finished surfaces or important center lines.
- Dimensions should be placed so that it is not necessary for the observer to calculate, scale, or assume any measurement.
- Dimensions should be attached to the view that best shows the shape of the feature to be dimensioned.
- Dimensions should not be placed on the object unless that is the only clear option.
- Overall dimensions should be placed the greatest distance away from the object so that intermediate dimension can nest closer to the object to avoid crossing extension lines.
- A dimension should be attached to only one view (i.e., extension lines should not connect two views).
- Never cross dimension lines.
- Never cross extension lines.
- A center line may be extended and used as an extension line.
- Leaders should slope at a 30, 45 or 60 degree angle.
- Dimension numbers should be centered between arrowheads, except when using stacked dimensions then the numbers should be staggered.
- In general, a circle is dimensioned by its diameter, an arc by its radius.
- Holes should be located by their center lines.
- Holes should be located in the view that shows the feature as a circle.
- Extension lines start approximately 1/16" from the object and extend 1/8" past the last dimension.
- The first dimension is 3/8" from the object and spaced uniformly 1/4" apart.
- Always dimension the actual size of the object - not the scaled size.
- Never dimension hidden lines.
- Never dimension the isometric view.
CHARACTERISTICS OF A GOOD CAD DRAWING
Accuracy -- Use object snap modes to accurately draw lines and other entities.
No Extra Entities -- Don't draw lines on top of lines, even on different layers.
Don't Add Entities to Connect! -- Don't add little short lines to lengthen existing lines. Use grips & lengthen existing entities!
Logical Layers -- Use layers to organize the drawing and make plotting clearer.
Conventional Colors -- We use yellow for the title block and black/white for object lines. Use other standard colors for other layers.
Title Block -- Include the following headings and the appropriate responses: DRAWN BY:, ASSIGNMENT #:, DATE:, SCALE:, BLOCK:, and PAGE #.
PLOTTING INSTRUCTIONS
- Select the PRINT or PLOT command.
- In the Printer/Plotter box, select the NCCPRINT2\ South High Room 507A DesignJet 550.
- Push the Properties button.
- Push the Custom Properties button.
- On the Paper/Quality tab (at the top) select the appropriate paper size (for B size, use "Oversize ARCH B"). For Lego Project, UseOversize ISO A3.
- Click on the Advanced button (near the bottom) and check the Auto Rotate box in the Advanced Paper Options and then select "24 inch roll" for Roll Size.
- Push the OK button.
- Push another OK button.
- One MORE time! AND AGAIN!!!!
- In the Paper Size box, verify that your selection is displayed.
- In the Plot Scale window, make sure 1:1 is displayed in Scale box (uncheck the Fit to Paper box).
- Plot Area should be set to Extents in the "What to plot' box.
- Select (Check Mark) Center the plot under Plot offset.
- Select Preview at the bottom left of the window.
- If it shows all of the title block, AND EVERYTHING IS CORRECT!!!! right click and press Plot. Yodaism: "If you do not LOOK, you cannot SEE!!"
- If it doesn't show all of the title block, recheck the settings, and re-do the necessary steps.
If it still doesn't preview correctly, contact Mr. Seibel