Descgeom 03 principal lines
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Transcript of Descgeom 03 principal lines
![Page 1: Descgeom 03 principal lines](https://reader035.fdocuments.us/reader035/viewer/2022062711/55c127bdbb61eb0f098b47be/html5/thumbnails/1.jpg)
Principal Lines
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Rule 4: True length of line• A line will appear in its true
length in a view taken such that that the fold line is parallel to the current projection.
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Principal lines• Principal lines are parallel
to at least one of the principal projection planes.
• A principal line appears in true length in the principal projection plane to which it is parallel, and appears parallel to the folding line in the adjacent views.
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Types of Principal Lines• There are three basic types of principal lines:• Horizontal line• Frontal line• Profile line
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Horizontal lines• A horizontal principal line is
parallel to the horizontal (top) projection plane.
• A horizontal principal line appears in true length in the horizontal (top) view.
• A horizontal principal line appears
• parallel to the TF folding line in the front view and parallel to the TR folding line in the right side view.
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Frontal lines• A frontal line is parallel to
the frontal projection plane, and appears in true length in the frontal view.
• A frontal line appears parallel to the TF folding line in the top view and parallel to the FR folding line in the right side view.
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Profile lines• A profile line is parallel to
the profile (right side) projection plane, and appears in true length in the right side view.
• A frontal line appears parallel to the FR folding line in the front view and parallel to the TR folding line in the top view.
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SAMPLE PROBLEMS 8
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Sample Problem #1• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 1:• Since the front view of line
1-2 in the F-plane is parallel to the H-plane, it means that horizontal view of line 1-2 will be in true length. 10
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 2:• Since point 2 should align
vertically between H and F plane, projecting the position of point 2 to the H plane shows the possible location of point 2. 11
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 3:• Since the true length is in
H-plane, make a 70mm line from point 1 and rotate it until it hits the possible location of pt. 2.
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 4:• Note that there are two
possible locations of pt. 2, but the problem describes it to be behind point 1.
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 5:• Having located pt. 2 in the
H-plane, simply project its position to the P-plane to locate its position in that plane.
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 6:• Since line 1-3 is a frontal
line, point 3 should be aligned with point 1 at a position parallel to the F-plane.
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 7:• Since line 2-3 is a profile
line, pt. 3 should be aligned with pt. 2 at a position parallel to the P-plane. This locates the position of pt. 3 in H-plane. 16
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 8:• Since line 1-3 is a frontal
line, draw a 80mm line from pt. 1 then rotate it until it hits the possible location of pt. 3. This completes the front view. 17
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 9:• The profile view can easily
be completed by projecting the locations of pt. 3 in the P-plane.
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Sample Problem #1 (Answer)• Line 1( 20,15,25) - 2(75, ?,
25) is 70mm long (2 behind 1). Line 1-3 is a 80mm frontal line, and line 2-3 is a profile line. Find the true length of line 2-3.
• Step 10:• Since line 2-3 is a profile
line, simply measure line 2-3 in the P-plane to get its true length.
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Sample Problem #2• Point 5 is on line
1(20,65,90) – 2(60,15,25), 35mm below point 1. Point 6 is on line 3(90,5,25) – 4(140,80,80). Line 5-6 if frontal. Find the true length of line 5-6.
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Sample Problem #2(Answer)• Point 5 is on line
1(20,65,90) – 2(60,15,25), 35mm below point 1. Point 6 is on line 3(90,5,25) – 4(140,80,80). Line 5-6 if frontal. Find the true length of line 5-6.
• Step 1:• Since pt. 5 is 35mm below
pt. 1 on line 1-2, we can easily locate pt. 5 in the F-plane.
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Sample Problem #2(Answer)• Point 5 is on line
1(20,65,90) – 2(60,15,25), 35mm below point 1. Point 6 is on line 3(90,5,25) – 4(140,80,80). Line 5-6 if frontal. Find the true length of line 5-6.
• Step 2:• Projecting pt. 5 from the F-
plane to the H-plane helps us locate pt. 5 in the H-plane, which should also be on line 1-2. 22
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Sample Problem #2(Answer)• Point 5 is on line
1(20,65,90) – 2(60,15,25), 35mm below point 1. Point 6 is on line 3(90,5,25) – 4(140,80,80). Line 5-6 if frontal. Find the true length of line 5-6.
• Step 3:• Since line 5-6 is a frontal
line, it follows that line 5-6 in the H-plane should be parallel to the F-plane. Pt. 6 is also on line 3-4. 23
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Sample Problem #2(Answer)• Point 5 is on line
1(20,65,90) – 2(60,15,25), 35mm below point 1. Point 6 is on line 3(90,5,25) – 4(140,80,80). Line 5-6 if frontal. Find the true length of line 5-6.
• Step 4:• Projecting pt. 6 from H-
plane to F-plane helps us locate pt. 6 on the F-plane, which should be on line 3-4 24
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Sample Problem #2(Answer)• Point 5 is on line
1(20,65,90) – 2(60,15,25), 35mm below point 1. Point 6 is on line 3(90,5,25) – 4(140,80,80). Line 5-6 if frontal. Find the true length of line 5-6.
• Step 5:• Since frontal view of line 5-
6 is now complete, the true length can now be determined.
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SEATWORK PROBLEMS 26
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Seatwork Instructions:• Use a short bond paper.• Place margin all around at
10mm from edge of paper.• Draw a horizontal line
20mm below top margin to create a panel where you will write the word problem.
• Divide the rest of the space in equal parts depending on the requirement of the problem
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Seatwork Problem #3-1• Line 1(10, ?, 80) - 2(10, 20,
25) is 70mm long. The front view of line 2 - 3(70, ?, 25) is true length as indicated. Complete the views of triangle 1-2-3
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Seatwork Problem #3-2• Line 2(60,15,80) –
3(60,55,?) is 60mm long. Line 3 - 1(20,15,?) is horizontal. How long is line 1-2?
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