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Thursday, September 20, 2007
Tuesday, September 11, 2007
Tips for Projection of Straight Lines
- The simplest position a straight line occupies in a space is, it is parallel to both V.P and H.P.
- The above position resulting in straight line as a top view and front view.
- For any other position first assume the given line parallel to both the planes.
- Then decide the view which will give us the true length of the line and true inclination.
- Rotate this view to the given angle to get the final view.
- Project from it to get the other final view.
For example:
- If a line is inclined to H.P, the front view will have the true length and true inclination.
- Therefore rotate the front view to the given angle (θ -theta) and project this line to get final top view.
- If a line is inclined to V.P, the top view will have the true length and true inclination.
- Therefore rotate the top view to the given angle ( φ-phi) and project this line to get final front view.
(Picture Coutesy:http://www.georgehart.com/cccg/Image71.jpg)
Monday, September 10, 2007
Tips for Projections of Points
I quadrant(Point above H.P & in front of V.P)
Front view above XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view below XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
II quadrant (Point above H.P & behind V.P)
Front view above XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view also above XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
III quadrant(Point below H.P & behind V.P)
Front view below XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view above XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
IV quadrant (Point below H.P & in front of V.P)
Front view below XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view below XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
Front view above XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view below XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
II quadrant (Point above H.P & behind V.P)
Front view above XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view also above XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
III quadrant(Point below H.P & behind V.P)
Front view below XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view above XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
IV quadrant (Point below H.P & in front of V.P)
Front view below XY reference line - Denoted by corresponding small letters with dash(')
Distance with respect to H.P
Top view below XY refernce line - Denoted by corresponding small letter only
Distance with respect to V.P
(I thank PSNACET students who developed and circulated the above tips informally)
Example Problem.
Some times combination of two points may be given in the problem like the following one
7.
A point E is 20mm below HP and 30mm behind VP. Another point F is in front of VP and above HP. The distance between the projectors of the points is 60mm. Determine the position of point F, if the lengths of the lines joining the plans and elevations of the points E and F are 80mm and 90mm respectively. (KVN.Ex.No.7, Page.No.?? )
As usual the projections of point E namely e and e' are fixed.
Mark o2 as o1 o2 = 60mm. With e as centre and ef = 80mm as radius cut an arc on a perpendicular to XY line from o2 meeting it below XY. The meeting point f is the plan of the point F.(since this point lies in III quadrant)
Similarly with e' as centre and radius e' f'=90mm cut an arc on the perpendicular to XY from o2 meeting it above XY. The meeting point f' is the elevation of point F.
Answer: Position of the point F
Measure o2 f' to represent the distance of the point F above HP.
Measure o2 f to represent the distance of point F in front of VP.
Monday, September 3, 2007
Introduction
The best way to introduce drawing to engineers is to quote from Borges words on Geometry as follows
The line is made up of an infinite number of points; the plane of an
infinite number of lines; the volume of an infinite number of planes; the hypervolume of an infinite number of volumes.... No, unquestionably this is not - more geometric- the best way of beginning my story.[Courtesy:http://math.cofc.edu/kasman/MATHFICT/mfview.php?callnumber=mf496
Picture Courtesy:http://blogs.mie.utoronto.ca/roller/moradian/resource/echer2.png]
After all engineers don't want their job end up in an illusion, like the picture above!!!...
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