Wednesday, June 29, 2011

DRAWING PINION GEAR

 DRAWING WORK PINION GEAR

DRAWING PINION GEAR

Tuesday, June 21, 2011

DRAWING FLEXIBLW CLUTH

DRAWING WORK FLEXIBLE CLUTCH
DRAWING FLEXIBLE CLUTC

DRAWING RESERVOIR TANK

                                                                                             
DRAWING WORK RESERVOIR TANK





DRAWING RESERVOIR TANK





DRAWING CUTTING HALF RESERVOIR TANK

Thursday, June 16, 2011

carriage drawing






                                                               (work drawing carriage)



                                                                                 CARRIAGE DRAWING

Wednesday, June 15, 2011

3D Modeling


3D modeling is the “process of developing a mathematical representation of any three-dimensional surface of object… via specialized software.”1 The process of 3D modeling and the cost of 3D modeling software are not easy to cope up with.2 Dedicated programs or application components are used in creating 3D models, and sometimes scene descriptions languages are involved. At other times, modeling is merely a part of a creation process.1 And the “most powerful tool” is our imagination.5 3D models are seen everywhere: in movies, in product designs, in advertisements, etc, but this does not mean that they are easily created.2 Creating 3D models is not as easy as creating 2D ones.5 3D models are “objects that are constructed on three planes.”2 They are composed of points connected by geometric entities. Examples of geometric entities are triangles, lines, curved surfaces, etc. There are two ways to create models: automatic and manual (which is similar to sculpting). They are made by hand, algorithmically, or scanned.1


3D computer graphics are “programs used to create 3D computer-generated imagery.” Some of these programs are specifically developed for certain objects only, such as chemical compounds or internal organs, and for certain processes only, such as skeletal animation.1,3 Users of 3D computer graphics interact with each other in forums to share their ideas. They share some tips and tricks on how to use graphics software. For example, three or more designers can collaborate on a project. A sub-forum is a “great place to share your experiences and do your Q&A with other users.” Groups are “starting points for discussions and collaborations.”5

Tessellation is the “process of transforming representations of objects, such as the middle point coordinate of a sphere and a point on its circumference into a polygon representation of a sphere.” This is used in breaking down primitives (spheres, cones, etc) to meshes (interconnected triangles). Lighting is an “important aspect of scene setup” and a “significant contributing factor to the resulting aesthetic and visual quality of the finished work.”1


The following are the three basic phases of the process of creating 3D graphics:2

1. 3D modeling
2. 3D animation
3. 3D rendering

Majority of solid models belongs to one of the following categories:1

* Solid
* Shell/Boundary

Solid models are realistic models that are hard to build. They have uses in non-visual simulations and in visual applications. Examples of non-visual simulations are medical and engineering simulations. Examples of visual applications are ray tracing and constructive solid geometry. Compared to solid models, shell/boundary models are easier to deal with. The exteriors of these objects define their boundaries. For instance, the focus of a shell/boundary model is its surface and its boundaries but not its volume.1

The following are digital approximations that are required to be used for nonfinite surfaces:1

* Polygonal meshes
* Point-based representations
* Level sets

Polygonal meshes are the “most common representation.” However, point-based representations are now gaining popularity. Level sets are a “useful representation for deforming surfaces which undergo many topological changes.” An example of these surfaces is fluids.1

The following are popular ways to represent models:1

* Polygonal modeling
* NURBS (Non-Uniform Rational B-Spline) modeling
* Splines and patches modeling
* Primitives modeling
* Sculpt modeling

The flexibility and ease of rendering have caused users to create a lot of models using polygonal modeling. NURBS modeling and splines and patches modeling are similar with each other in terms of their dependence to curved lines in defining visible surfaces. But if it is based on flexibility and ease of use, splines and patches modeling falls between the first two: polygonal modeling and NURBS modeling. Primitives modeling is more suitable to use in technical applications that does not have much organic shapes. It provides the following benefits: quick and easy construction, mathematically defined and absolutely precise forms, and simpler definition language. Geometric primitives serve as the building block of its models. Examples of these primitives are balls, cylinders, cones, etc.1

There are two types of sculpt modeling:1

* Displacement
* Volumetric

Both of them allow a very artistic exploration of the model. However, the former is more popular than the latter.1

Some modeling techniques are the following:1

* Constructive solid geometry
* Implicit surfaces
* Subdivision surfaces

3D modeling has advantages over 2D methods. These are the following:1

* Flexibility
* Ease of rendering
* Accurate photorealism

Flexibility is the “ability to change angles or animate images with quicker rendering of the changes.” Ease of rendering results from an automatic calculation and rendering, and mental visualization and estimation. Accurate photorealism is marked by minimized human errors in applying visual effects. However, sometimes it is difficult to achieve certain photorealistic effect. This is one disadvantage of 3D modeling.1

3D Modeling, Drafting, Product Design, Pro/ENGINEER, SolidWorks

Definition of Terms

3D Modeling, Drafting, Product Design, Pro/ENGINEER, SolidWorks

2D drawing

- An indirect and incomplete representation of an engineering product or system, subject to interpretation and error1

3D
- A real object or true depiction of real image1
3D computer graphics
- Graphics that use a three-dimensional representation of geometric data… that is stored in the computer for the purposes of performing calculations and rendering 2D images3
3D computer graphics software
- Programs used to create 3D computer-generated imagery9
3D model
- The product of 3D modeling2
- An object that is constructed on three planes27
3D modeling
- The process of developing a mathematical representation of any three-dimensional surface of object… via specialized software2
- The construction, manipulation, and storage of geometric objects to represent objects… around us or virtual objects17
3D printing
- A form of additive manufacturing technology where a three dimensional object is created by successive layers of material6
3D rendering
- The 3D computer graphics process of automatically converting 3D wire frame models into 2D images with 3D photorealistic effects on a computer5
3D wireframe
- Extension of 2D drafting12

Assembly modeling
- Technology and methods used by Computer-aided design and Product visualization computer software systems to handle multiple files that represent components within a product15

Computer-aided design (CAD)
- The use of computer technology for the design of objects, real or virtual12
- A combination of both hardware & software that helps architects, engineers and related professionals in the real estate & manufacturing industry worldwide18
- An important industrial art extensively used in many applications, including automotive, shipbuilding, and aerospace industries, industrial and architectural design, prosthetics, and many more12
- A major driving force for research in computational geometry, computer graphics (both hardware and software), and discrete differential geometry12
- Especially important technology within the scope of computer-aided technologies, with benefits such as lower product development costs and a greatly shortened design cycle12
- One of the many tools used by engineers and designers and is used in many ways depending on the profession of the user and the type of software in question12
- One part of the whole Digital Product Development (DPD) activity within the Product Lifecycle Management (PLM) process12
Computer-aided geometric design (CAGD)
- The design of geometric models for object shapes, in particular12
Computer animation or CGI animation
- The art of creating moving images with the use of computers10
- An artful blend of creative vision and technology31

Design intent
- How the creator of the part wants it to respond to changes and updates4
DWGgateway
- A free data translation tool that enables any AutoCAD software user to open and edit any DWG file, regardless of the version of AutoCAD it was made in4

eDrawings Professional
- An e-mail-enabled communication tool for reviewing 2D and 3D product design data across the extended product development team4
Electronic design automation (EDA or ECAD)
- A category of software tools for designing electronic systems such as printed circuit boards and integrated circuits26

Features
- Building blocks of the part4
- The shapes and operations that construct the part4
FeatureWorks
- Feature recognition software that lets designers make changes to static geometric data, increasing the value of translated files4
Flexibility
- The ability to change angles or animate images with quicker rendering of the changes2

Group
- A starting point for discussions and collaborations28

Innovation
- A vital ingredient of business success29
Interoperability
- The key issue which integrates various CAD CAM CAE tools1

Kinetic design
- Aesthetic design of physical movement32

Level sets
- A useful representation for deforming surfaces which undergo many topological changes2
Lighting
- An important aspect of scene setup2

MACRO (merge and correlate recorded output)
- Anything more than a single command19
- Rule or pattern that specifies how a certain input sequence should be mapped to an output sequence according to a defined procedure20
Macro program
- Computer programs that capture the user’s actions as if it is recording the user21
MoldflowXpress
- A mold design validation tool that was built into a solid modeling environment4

Parameters
- Constraints whose values determine the shape or geometry of the model or assembly4
Polygonal modeling
- An approach for modeling objects by representing or approximating their surfaces using polygons8
Print3D
- A 3D printing feature that allows users to convert their 3D CAD model to a .STL file and then have it sent to specialty manufacturers for quote4
Procedural modeling
- An umbrella term for a number of techniques in computer graphics to create 3D models and textures from sets of rules7
Product design
- The efficient and effective generation and development of ideas through a process that leads to new products30
Pro/ENGINEER
- A parametric, integrated 3D CAD/CAM/CAE solution created by Parametric Technology Corporation13
- The first to market with parametric, feature-based, associative solid modeling software13
- An integral part of a broader product development system developed by PTC13
- A piece of software that falls within the category of CAD/CAM/CAE and site alongside other similar products currently on the market13
- A feature based modeling architecture incorporated into a single database philosophy with advanced rule based design capabilities13

Skeletal animation
- A technique in computer animation, particularly in the animation of vertebrates, in which a character is represented in two parts: a surface representation used to draw the character… and a hierarchical set of bones used for animation only11
Solid modeling
- A consistent set of principles for mathematical and computer modeling of three dimensional solids14
SolidWorks
- A 3D mechanical CAD… program that runs on Microsoft Windows and was developed by Dassault Systèmes SolidWorks… a subsidiary of Dassault Systèmes4
- A competitor to CAD programs such as Pro/ENGINEER, I-DEAS, Unigraphics, and CATIA4
- A parasolid-based solid modeler4
SolidWorks Flow Simulation
- A tool that tests fluid-flow simulation and thermal analysis so designers can conduct tests on virtual prototypes4
SolidWorks MoldBase
- A catalog of standard mold base assemblies and components4
SolidWorks Motion
- A virtual prototyping tool that provides motion simulation capabilities to ensure designs function properly4
SolidWorks Simulation
- A design validation tool that shows engineers how their designs will behave as physical objects4
SolidWorks Simulation Premium
- A design validation tool that caters to designers without engineering background4
SolidWorks Sustainability
- A product that measures the environmental impact of designs while they are modeled in SolidWorks4
SolidWorks Toolbox
- A library of parts that uses “Smart Part” Technology to automatically select fasteners and assemble them in the desired sequence4
SolidWorks Utilities
- Software that lets designers find differences between two versions of the same part, or locate, modify, and suppress features within a model4
SolidWorks Viewer
- A free plug-in for viewing SolidWorks parts, assemblies, and drawings4
SolidWorks Workgroup PDM
- A PDM tool that allows SolidWorks users operating in teams of 10 members or less to work on designs concurrently4
Sub-forum
- A great place to share your experiences and do your Q&A with other users28

Technical drawing or Drafting
- The academic discipline of creating standardized technical drawings by architects, interior designers, drafters, design engineers, and related professionals16
- Integral communication of technical or engineering drawings and is the industrial arts sub-discipline that underlies all involved technical endeavors16
- Means of clearly and concisely communicating all of the information necessary to transform an idea or a concept into reality22
- Drawing plan, rendered to scale, used to communicate direction and specifics to a group of people creating something23
- Formal and precise way of communicating information about the shape, size, features and precision of physical objects24
- Universal language of engineering used in the design process for solving problems, quickly and accurately visualizing objects, and conducting analysis24
- A graphical representation of objects and structures24
- Expression of bodies by lines24
- Skill, a vocation25
Tessellation
- The process of transforming representations of objects, such as transforming the middle point coordinate of a sphere and a point on its circumference into a polygon representation of a sphere2
- A significant contributing factor to the resulting aesthetic and visual quality of the finished work2
Read more at http://www.articlealley.com/3d-modeling-2277615.html?ktrack=kcplink

Tuesday, June 14, 2011

Drafting/Technical Drawing

What is Technical Drawing?

Many references provide a lot of definitions for technical drawing. A technical drawing or drafting is the “academic discipline of creating standardized technical drawings by architects, interior designers, drafters, design engineers, and related professionals.” It is an “integral communication of technical or engineering drawings and is the industrial arts sub-discipline that underlies all involved technical endeavors.1” It is a “means of clearly and concisely communicating all of the information necessary to transform an idea or a concept into reality.2” It is a “drawing plan, rendered to scale, used to communicate direction and specifics to a group of people creating something.3” It is a “formal and precise way of communicating information about the shape, size, features and precision of physical objects,” a “universal language of engineering used in the design process for solving problems, quickly and accurately visualizing objects, and conducting analysis,” and “a graphical representation of objects and structures.” It is also the “expression of bodies by lines.4” It is a “skill, a vocation.5” A good technical drawing is “one that properly and conveniently communicates all of the information needed to transform a design into a product that meets or exceeds customer expectations.2”


Technical drawings have many uses in many kinds of applications specially where there is a need for designs and conversion processes, such as those found in manufacturing, engineering, architecture, and construction. Because technical drawings have many uses, there is a need to regulate practices that are involved in creating these drawings. Drafters use standards of practice, of which the most widely used are practices of the US Department of Defense (DOD), the US Military (MIL), the American National Standards Institute (ANSI), and the American Society of Mechanical Engineers (ASME).2 Drafters use many geometric figures and symbols to specify the scope and details of a product because it is very important that technical drawings be accurate.3 Drafters create technical drawings using freehand, mechanical, or computer methods.4 Processes that are involved in drafting are sometimes time-consuming.1 One thing that determines the ultimate quality of a product is the quality of its technical drawing. We know if a technical drawing is a good one when developers for a design should no longer need to consult designers or drafters of the drawing because all information that these developers need are already included in the drawing.2 In essence, technical drawing is about linear projection.5

A Quick Summary of the History of Technical Drawing

Technical drawings are things that are not new. Even during the times of early Greek civilization, technical drawings existed. These drawings were scratched on the floor to guide workers while they were building. As time went on, people learned to use mechanical devices on drafting tables to draft. Nowadays, drafters or designers use computers to aid them in their design works.3 Computers lessened the effort needed by designers to accomplish their tasks. Before the widespread use of drafting software, drafters were required to have an extensive knowledge on the principles of descriptive geometry and to use tools such as t-square, compass, and drafting table. Now, descriptive geometry is no longer used very often because computers do much of the computations. With the use of computers and knowledge in linear algebra, data, such as coordinates of points and their projection on planes, are computed more easily, and designers can now bypass some rules or principles on how to draw correctly.5
Methods of Technical Drawing

The three methods in technical drawing are the following:1

* Sketching
* Manual or by instrument
* Computer-aided design (CAD)

A sketch is a “quickly executed freehand drawing that is not intended as a finished work.” It is a “quick way to record an idea for later use.” Sketches serve as abstractions or summaries of complex patterns or design solutions. Because their purpose is to summarize, sketching results to an enhanced design process. In a way, these sketches aid in the design collaboration.1

In manual drawing, it is very important to have an accurate drafting table and to give much attention to the positioning of drafting tools. Drafters use a wide array of mechanical instruments and tools, such as compasses and French curves. Drafters of manual drawings are skilled in geometry, trigonometry, and spatial comprehension. They have mastered the mechanics of drawing lines, arcs, and circles, and they are expected to be precise and accurate in giving technical details. One procedure in manual drafting involves using a drafting table with a paper over it, and sliding a T-square across the side of the table over the surface of the paper. Drafters run pencils or technical pens along the edge of the T-square to create parallel lines. Sometimes, the T-square is used to hold other smaller drawing tools, such as squares and triangles. With the use of these smaller drawing tools, drafters could draw lines from different angles. When tasks become repetitive already, drafters use templates, and these templates were made for some specific tasks. Templates are commercially available, but sometimes, drafters prefer to create their own.1

Manual drawings must be redrawn from scratch when there is a need to modify them. This difficulty was removed by the use of CAD systems. A CAD system is either 2D or 3D. A 2D CAD system is “merely an electronic drawing board.” 2D CAD systems are capable of producing drawings of large projects such as plans for a building or an aircraft, but they do not have the capability to allow designers to test whether components and parts will fit together. These kinds of projects require designers to use 3D CAD software for the modeling, assembling, and checking of components before the actual release of technical drawings to manufacturers.1

CAD systems, such as AutoCAD, SolidWorks, and Pro/ENGINEER, automate and accelerate the mechanics of drafting tasks. These systems support symbols for common components that are found in many disciplines, such as electrical, electronic, pneumatic, and fluidic. CAD designers follow standards such as those provided by BS and ISO, but, sometimes, it is up to designers to create drawings.
Read more at http://www.articlealley.com/article_2277658_50.html?ktrack=kcplink

Monday, June 13, 2011

QCAD: Technical drawing with Linux

General Notes

A "plan" is any precise plane representation of a real object for study or for production purposes. The dimensions of each element (entity) of which the drawing consists of, must be exact no matter what scaling is used. This differentiates a CAD program from a vectorial drawing tool such as Sketch, Illustrator or Corel Draw, which is a more or less faithful representation of reality. With CAD a plan first of all has to be exact. This is in contrast to illustrations (Drawing) where the aesthetics of a picture are of more concern.  

Installation of QCad

The version qcad-1.4.x used for this article is on the applications CD of the Redhat and Mandrake distributions as ready-made package. Other distributions surely have similar packages. You can download the newest version at http://www.qcad.org/. Qcad needs QT 2.2 as GUI library.  

A little bit of theory

Before beginning with your first document you should have understood certain CAD concepts and definitions.  

The entities

An entity is a layout element that is "known" to the program by its form (segment, arc...), in the geometric characteristics of its position (vertical, tangent...), in its start and end positions which determine its dimension (fixed at intersections, coordinates, center...), in its attributes (color, thickness, types of characteristics) and its membership to a layer (blue print). Generally speaking to build an entity, it is necessary:
  • to define your view on the working layer
  • to define the attributes
  • to choose the nature: straight line, segment, circle, ellipse, point, curve, hatch, text...
  • to indicate the geometric framework of the construction: horizontal, oblique, concentric, vertical...
  • to indicate the constraints
It results in building a virtual but exact sentence of this kind: circle of radius X from the center passes through the endpoints of an entity which was indicated by a right click , etc. The points will have to be indicated by a left mouse click near the desired points which have to be chosen among those that the system offers. It should be noted that the concept of fixation is found elsewhere under the name <snap> For example the sentence horizontal straight line, which touches the outer lines of an entity is composed with the following menus and sub-menus:


[qcad00.png]

Note: That you get to the first start menu by clicking with the right mouse button onto the "paper".
 

The layers

Elsewhere called levels, plans, blue prints. The layers describe in fact a virtual pile of celluloids. Each celluloid contains a part of the drawing, recognizable as a whole if you look on the pile from above, thanks to its transparency. A layer can be moved in the pile, removed (which affects only the part of the drawing that it contains), frozen or made invisible. The layer on which you work is the only active one at the moment. The operations that you carry out affect only it. When you assign attributes of color, line types or line thickness then all entities that you draw will have them by default. However you could assign blue to an entity that is on a red layer by modifying its properties. For a complex drawing you will work on one layer after the other which allows to make a certain subset visible or invisible, print only one piece, modify nothing but this.  

The status line

The status line is located in the lower part of the main window. It is not specific to CAD software programs but nevertheless essential. As a command requires several successive operations carried out in a defined order, the program shows in the status line the operations that should follow and what it expects from you and this until the end. It is therefore absolutely necessary to read the information that is displayed in that lower line if you do not want to risk that the CAD session ends with the declaration that this is a +-@-#!! program. In CAD the result is precise if the designer is working exactly and systematically.


[qcad01.png]


 

Methods of drawing

There are several ways how to do it, with at least two of them being excellent. Both use the concept of drafts based on not dimensioned (very long) straight lines but with precise relative positions (distance of one compared to the other). These straight lines, horizontal and vertical are called lines of construction in DTM or SoildWork and geometries in TSCadDraw. The first method consists of defining a profile based on these straight lines as points of support. The exercise which we will follow in the rest of this article will demonstrate this.
The second method consists of defining a profile by adjusting the lines at fitting intersections. To do this with QCad you have to right click to get back to the main menus and then choose <edit><Trim two object> then click on the line that you would like to trim (cut) next click on the line where your first line should stop. Here are 3 examples of editing objects:


[Three examples of the function Edit]


In this figure as in the following ones the yellow boxes show the selected functions, footnote: not colored by QCad itself, and the blue crosses show corner points on which you can click. With the function <Trim objects> one makes an element fit to another. It is important to click first (1) on the part that you want to fit and second (2) on the entity that intersects the first. For the function <Bevel> it is important to determine the X and Y values of the edge before, no matter if it is trimmed or not and finally to click on the entity to be beveled. The steps are the same when working with intersecting lines and the function <Round>. One should also mention that QCad tries to be quicker than the user or tries to help you with your decision, in fact when a function is activated which needs the selection of a second entity to go on, then QCad modifies the color of that entity which is near the pointer and indicates to you that you can select it with a left mouse click. It works the same way with the fixation points which are colored red. The right mouse click cancels an operation and allows you to go back to the main menu. The following figure shows the result of these various adjustments:


[The result]


 

Example application

To get to know a program there is nothing better than to use it. Let's try to draw an object which is inspired by the logo of SEV Marchal which I usually use for my beginner's courses in numerical control. With DMT 10 by Mécasoft it can be drawn in less than 5 minutes, annotations included.


[SEV Marchal logo]


 

Set up of a page format

This is not strictly necessary for the exercise but a technical drawing obeys to standards which define among other things the view and the aspect of the format (frame and data block) in which they are contained. Here I use a format coming from DMT10 transferred to DXF, the only file type that QCad can read and generate which in turn guarantees the exchange in two directions with all CAD programs in the world. Once the format is loaded you see a mark off of the drawing zone with a zero reference in the middle of the area. It is recommended to delete unnecessary layers, to rename those which contain the format frame and to add those that are described in the following paragraphs.

[qcad05.png]


 

Managing the layers

By clicking on the icon representing several piled up pages you open a side window called "Layer List". The selected blue print becomes the active blue print, it appears with intensified brightness. The eye besides the name of the layer allows to make it visible or invisible. The open eye to the very right of the layer list window makes all layers visible while the closed eye makes them invisible. The plus sign adds a layer to the list, the minus sign eliminates the selected layer, the symbol REN allows to rename the selected layer and the trash can deletes all empty layers. Now we need a layer <Format A4> that contains the frame, a layer <Trait> that contains the drawing in a front view and a layer <Annotation> that contains the annotations to the drawing.

[qcad06.png]


 

Defining a vertical reference

This straight line passes through the origin (zero) and allows the construction of parallels on the X-axis. Our drawing will be symmetrical to this line. At first you activate the layer <Trait>; then you choose a continuous width type with a thickness of 1 and the color red (point 5) then you construct the "sentence" <straight line><vertical(1)><passing through absolute coordinates(2)> <enter 0,0(3)> <click left(4)>

[reference line]


 

Construct a parallel to 60

If necessary you remove the menus by several right mouse clicks and construct the following: <straight line>< Create parallels><enter 60> and approach the position marks of the reference straight line. It will become grey in turn and according to the position of the pointer QCad suggests to construct the parallel either to the right or to the left of the reference. Position the pointer slightly to the left and make a left mouse click. A straight line in cyan is created.

[parallel line, distance 60]


 

Construct the other straight lines

Most functions of QCad are repetitive, that is, they are active as long as they aren't replaced by another. Therefore <straight line><Create parallel><Distance of > is still activated. It is sufficient to replace the value 60 by 50 (Vertical 2) and to click and then to replace 50 by 25 (Vertical 3) and then to click. Go on with this for the horizontal straight lines which are defined with regards to the reference at 0 (Horizontal 4). Draw the horizontals (5) and (5') with distance 60, then (6) with distance 30 and finally (7) with distance 40.

[all the lines]


 

Construct the left half of the logo

For the construction we rely here on the straight lines which we have just drawn. You have to go back to the main menu with a right mouse click and choose <lines><multiple lines (button: create lines)>< passing through the intersection (Snap automatically to..)>. From this moment on when we position the pointer near the intersection of the straight lines it will be marked with a red circle. When this intersection is suitable as the beginning of a character segment, then make a left click, move to the next intersection and make a left mouse click again. The segment is drawn. But as the function is modal this last point which is the end of the segment that we have just drawn will at the same time be the beginning of the next segment. This allows the drawing of closed contours. If you don't need it for an additional segment a right click will interrupt the active function but doesn't cancel it. So for this half side of the profile choose a continuous line type, thickness 2 and color blue like in point 1 in figure QCad10 (below). Then left click on 2, 3, 4, 5, 6, 7, 8, 9 and finally a right mouse click. The left half of the profile is ready. Easy!

[qcad10]


 

Editing the result

Editing is a modification of something existing. To add an adjustment or a beveling to a drawn profile or to delete a segment, that are modifications. Whatever the changes to make are there is a general approach. First you choose the function <Edit (1)> which opens a sub-menu of all possible modifications. Select the desired function, e.g. <delete objects(2)>, which opens a sub-menu for selection: contour, all entities, tag single element... This allows you to choose the borders of the modification. If you choose for example <Tag single element(3)> design the element (4) and then acknowledge the action by a left mouse click on the arrow icon (5) then the chosen element is deleted. Please note that the function <(un-)tag single element;> is a toggle, if you click on an element then it is selected, another click and it is deselected. This allows to remove certain elements from a global selection.

[qcad11]


 

Adjusting the basis of the ear

Going back to the main menu we delete the construction straight line called 1 in figure QCad12 (below) and choose <Edit><Round><Radius 10> <trimming> We determine the entities to trim, then we move the pointer near to the adjustment/link that has to be made. Qcad then suggests possible solutions (radius 10). If a fitting point is suggested a left mouse click keeps the linking/adjustment and trims the line.

[qcad12.png]


 

To construct the mirrored half of the profile

With the existing 1/2 profile it would be nonsense to draw another one, therefore it is sufficient to duplicate the first one symmetrically to obtain a complete profile. We choose <Edit><mirror objects><Tag Range><Point (Snap to nothing)> and draw a window around the 1/2 profile (yellow frame in figure QCad13). The profile is selected: it becomes red. We make a right mouse click: we get back to the selected sub-menu. We acknowledge by clicking on the arrow icon. We get back again to the fixation sub-menu: we choose <Extremity (Snap to endpoints)> and determine the points 1 and 2 as shown in figure QCad13. A dialog box "Mirror" appears. If you type in a value of 0, the 1/2 profile is moved, if you give in a value of 1 it is duplicated. Therefore you have to give in a value of 1 and click <Ok>. And the profile is ready.

[qcad13]


 

Drawing the eyes

By using what we have seen already we can draw the left eye as well through the horizontal and vertical construction lines (point 1). Then you draw the profile by building upon this straight line with a polyline. You trim it with a radius 5 (green crosses) and a radius 25 (magenta cross, points 2 and 3); finally you delete the construction line and duplicate the left eye by mirroring it to the right (point 4). All necessary commands for this operation have already been explained above.

[qcad14.png]


 

Adding dimensions

Annotations are no strength of QCad: it is impossible to give tolerances or to write somewhere else than in the middle of the lines that indicate the dimensions. The consequence of this last point is that the size of the characters is changed depending on the available space between two reference points. This give the whole drawing a strange aspect. Well, no matter how it is, to make annotations you have: to position yourself on the annotation layer, choose a fitting line attribute, especially a thickness of 1 and a color different from the other lines, unique if possible. But this isn't obligatory. Select <Annotation (Sub-menu dimensions)><Type of annotation horizontal or vertical or radius...><Endpoints to determine the position of the construction lines or certain intersection (Snap manually to..)>< Point (Snap to nothing) for positioning the dimension> To change from one way of fixation to another you may use the short cut keys: F for <point>, E for <Extremity>, X for < automatic intersections> etc. The points A, B and C (image below) are difficult to annotate with a dimension.

[qcad15]


 

A sectional view (cut): preparation

The representation of a three dimensional object in 2D makes it necessary to order several views according to certain drawing norms even if it only is to show the thickness of the object. Our drawing represents an object of 20mm thickness worked on in a depth of 5mm. To just say this isn't explicitly enough and a cross sectional view becomes necessary. To do this: Make the layer <Annotation> invisible with a double click on the icon with the open eye. Add a layer <cross section> with the option + in the management menu for the layer. According to the norm a cross sectional cut is indicated by a line with a points and hyphens. Activate this as a style attribute and draw a line of width 1 between the eyes of our logo (<straight line><Polyline><snap to grid points>).

[qcad16.png]


 

Sketch the cross sectional view

In industrial drawing whether with pencil and paper or with CAD there must always be a correspondence between the views. The cross sectional view is a projection along the line that indicates the cross sectional cut through the object.

[qcad17.png]


 

Drawing and hatching of the cross sectional view

We use again straight construction lines to draw the cross sectional profile with a polyline (figure QCad18, below). Modify the properties of the lines for the hatch (2). Select <Create hatchings(3)> <Tag range> <Passing through the Point (Snap to nothing)> and draw a square around the cross sectional view to select the area (4). Acknowledge (5). The dialog box "Create hatchings" appears. We choose a fitting hatch parameter(6). We press OK (7) and the hatched view (8) is ready.

[qcad18.png]


 

And finally the finish

The cross sectional view as it is represented here is, according to the rules of industrial drawing, is a projection. Since obtain this view by virtually cutting our profile at the height of the eyes we have to indicate the depth of the eyes. You add this as follows <Straight polyline line (button line)><create lines> Now the drawing is ready. Only the frame of our paper (the data block) has to be filled in with text. I leave it to you to discover the < text function>.

[qcad19.png]


 

Conclusion

Linux CAD-Applications under the GPL aren't numerous. It is therefore appropriate to honor the authors of QCad and to thank them for the useful application they give to the community. Even though it isn't replacing industrial applications of the type of Cadkey, AutoCad or DMT, it remains a good educational tool and a tool for not too complex plans. One can regret the weaknesses of the annotation function, the absence of covering/lining/boarding functions (rowness, geometrical tolerances, sectional views) and the numeric limitation of the geometric border conditions. But you can congratulate the authors for the ease of handling, for the simple and convenient user interface, the powerfulness of linking/fitting and hatch functions, to the choice of the DXF format and not a proprietary format. Possibly as well to many other good things in QCad which I have not yet discovered. QCad has a help system but the documentation is English and remains therefore totally obscure to me. This proofs how easy the handling of QCad is. I have discovered everything by just playing around with the program.
Having said that, the optics of CAD have changed dramatically in the recent years. It is less a question to produce 2D drawings to represent three-dimensional objects. But to work out a 3D model completely defined in form and dimension with the help of performant tools and volume modelers. The program generates then automatically plans, annotations and the listing for numerically controlled machines. These programs are ProEngineer, SoldConcept, Catia, Solid Edge or Think3D.... When will these tools be available to Linux? At the moment we have QCad and CAM Expert, its commercial brother, equipped with two dimensional CAD and old MS-DOS products such as DMT10 by Mécsoft which runs perfectly in dos-emulation under Linux as you can see in the last screen shot (below).

[qcad20]

 

Sunday, June 12, 2011

How to Design a Shaft for a Constant Load


The shaft is a basic mechanical component of many machines. This article will discuss drive shaft design concepts and formulas by explaining a design problem for a shaft for a constant load.
You can see a shaft in almost every machine which has rotating parts. Typically a shaft has a circular cross section. However, the shaft with other cross-sections find special application. We will discuss the design concept of a drive shaft subjected to a fixed load.
A drive shaft is supported by bearings at both the ends (and at regular interval in the centre for longer shafts). The belt driven pulleys are usually placed over the shaft in between the bearings.
Basic Shaft Design Formula
The drive shaft with multiple pulleys experience two kinds of stresses, bending stress and shear stress. The maximum bending stress generated at the outer most fiber of the shaft. And on the other hand, the shear stress is generated at the inner most fiber. Also, the value of maximum bending stress is much more than the shear stress. So, the design of the shaft will be based on the maximum bending stress and will be driven by the following formula:
Maximum bending stress Tb = (M * r) / I……………….Eqn.1.1
Where,
M is maximum bending moment on the shaft.
r is the radius of the shaft.
I is area moment of inertia of the shaft.
Design Procedure
  • Draw the bending moment diagram to find out the maximum bending moment (M) on the shaft.
  • Calculate the area moment of inertia (I) for the shaft.
  • Replace the maximum bending stress (Tb) with the given allowable stress for the shaft material.
  • Calculate the radius of the shaft.
Shaft Design Problem
Shaft Design
Refer the above picture, where a steel shaft is supported by two bearings and a pulley is placed in between the bearings. You have to design the shaft. Weight of the pulley is 1000 N.
Input data:
Maximum allowable shear stress for the shaft material= 40 N/mm2
Solution:
  • From the bending moment diagram, the maximum bending moment (M) is calculated as 66666.67 N/mm2.
  • Area moment of inertia (I)of the circular shaft is:
I = pi * r^4 *0.25
= 0.785*r^4………………..Eqn. 1.2
  • From Eqn1.1 we can write:
40 = (66666.67 *r)/ (0.785*r^4)
r= 12.85 mm
  • So, the minimum radius of the shaft should be 12.85 or 13 mm.
Conclusion
The drive shaft design problem discussed in this article has considered only the self weight of the pulley and hence the load acting in only one direction. If the loads act in multiple directions then the resultant moments need to be calculated and then the shaft design formula applied. Another way of solving drive shaft design concept problem is using FEA tools.
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