Engi 1504 Graphics Lecture 6 Descriptive Geometry II
- Slides: 17
Engi 1504 – Graphics Lecture 6: Descriptive Geometry II l Properties of planes l Midterm issues l Class assignment # 7 Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 1
Properties of Planes l Two limiting cases of a plane: – True shape – Edge view l Can be used to solve any problem involving planes Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 2
Properties of Planes l l At least three lines are required to define a plane Edge view must be found before a true shape can be found Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 3
Finding the Edge view of a Plane l l l A plane will be seen as an edge if any line in it is seen as a point. It is often easier to add a line (where we want it) than to use an existing line Recall: a line must show true length before it can be seen as a point Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 4
Finding the Edge view of a Plane l l We can find the true length of any line (AB, BC, or CA) using an auxiliary plane parallel to it. Then we can find the line as a point, which will show the plane as an edge. This requires two auxiliary planes – there is an easier way! We will create a True length line in the plane. Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 5
Finding the Edge view of a Plane l l l Note: none of the given lines are parallel to a folding line, and hence not true length. So we construct a true length line in the plane and then show it as a point. This requires only one auxiliary view Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 6
Finding the Edge view of a Plane l l l Draw a line in the plane parallel True Length to a folding line (say in the front view). Project the endpoints into the top view. This line is true length Now we have a true length line, so all we have to do is show it as a point. Course: Engineering Graphics 1504 Memorial University of Newfoundland X 2 x 1 Sheet 7
Edge View of a Plane cont. l To find the point view of AX, we construct a folding line perpendicular to AX and project onto auxiliary plane 3 2 3 a 3 x 3 D Point view D Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 8
Edge View of a Plane cont. l Project B and C onto plane 3 and join the points to show plane ABC as an edge Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 9
True Shape of a Plane l l l If we place an auxiliary plane parallel to the edge view, then the plane can be seen as true shape. Recall: An edge view must be found first So we place an auxiliary plane parallel to the edge view and project the plane onto it Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 10
True Shape of a Plane l l Draw the plane in edge view. Place a folding line parallel to the edge view. Project all points onto the auxiliary plane (plane 4 in this case) and join them. Recall: the distance from the folding line is found from the view adjacent to the edge view (plane 2 here) Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 11
Plane shows true shape Course: Engineering Graphics 1504 a 4 b 4 c 4 Memorial University of Newfoundland Sheet 12
The Slope of a Plane l l The slope of a plane is the angle it make with the horizontal. Slope is seen only in the front or profile view (the elevation views) Recall: slope can only be determined from a true length line. So, the TL line used to find the edge view of the plane must be in the top view so that the edge of the plane appears in the horizontal view Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 13
The Slope of a Plane l l l Create a TL line in the horizontal view Find the edge view of the plane Measure the angle it makes with the horizontal Course: Engineering Graphics 1504 Memorial University of Newfoundland 54 o slope Sheet 14
The Strike of a Plane l l The strike of a plane is the angle that a true length line in the plane makes with the North (top view) So strike is the bearing of the horizontal line AX Course: Engineering Graphics 1504 N strike Memorial University of Newfoundland 54 o slope Sheet 15
Summary Find edge view of a plane: 1. 2. Draw a line parallel to a folding line and project the line into the adjacent view, where it will be true length Find a point view of this line and project other points in the plane. The plane will appear as an edge Find true shape of a plane: 1. 2. Find edge view of a plane and create an auxiliary view parallel to the edge view Project the points defining the plane onto this auxiliary view. The plane will be true shape Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 16
Break Time l Take 5 minute break Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 17
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