5.1 A parallel key must be machined to fit onto an 84 mm diameter shaft. Calculate the following: 5.1.1 The width of the key 5.1.2 The thickness of the key 5.1.3 The length of the key 5.2 A spur gear with 106 teeth must be cut on a milling machine. Calculate the simple indexing needed to cut this gear with the help of a Cincinnati dividing head. (HINT: H = 0,866 P) 5.3 The pitch of a metric V-screw thread is 2 mm. Calculate the depth of the screw thread. 5.4 A spur gear has 48 teeth and a module of 3. Calculate the following: 5.4.1 Addendum 5.4.2 Dedendum 5.4.3 Clearance 5.4.4 Pitch-circle diameter (PCD) 5.4.5 Outside diameter 5.4.6 Cutting depth 5.4.7 Circular pitch 5.5 Identify the type of key shown in FIGURE 5.5 below. 5.6 Identify the milling process shown in FIGURE 5.6 below. 5.7 Identify the engineering equipment shown in FIGURE 5.7 below.

NSC Mechanical Technology Fitting and Machining Drill and key sizes: 5.1 A parallel key must be machi

5.1 A parallel key must be machined to fit onto an 84 mm diameter shaft - NSC Mechanical Technology Fitting and Machining - Question 5 - 2018 - Paper 1

Question 5

5.1 A parallel key must be machined to fit onto an 84 mm diameter shaft. Calculate the following: 5.1.1 The width of the key 5.1.2 The thickness of the key 5.1.3 ... show full transcript

Worked Solution & Example Answer:5.1 A parallel key must be machined to fit onto an 84 mm diameter shaft - NSC Mechanical Technology Fitting and Machining - Question 5 - 2018 - Paper 1

Step 1

5.1.1 The width of the key

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Answer

To calculate the width of the key, use the formula:

ext{Width} = \frac{D}{4}

Substituting the diameter (D = 84 mm):

ext{Width} = \frac{84}{4} = 21 \, ext{mm}

Step 2

5.1.2 The thickness of the key

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Answer

The thickness of the key is calculated using the formula:

ext{Thickness} = \frac{D}{6}

Substituting the diameter:

ext{Thickness} = \frac{84}{6} = 14 \, ext{mm}

Step 3

5.1.3 The length of the key

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Answer

The length of the key is determined using the following formula:

ext{Length} = D \times 1.5

Substituting the diameter:

ext{Length} = 84 \times 1.5 = 126 \, ext{mm}

Step 4

5.2 Calculate the simple indexing

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Answer

For simple indexing, we use:

ext{Indexing} = \frac{40}{n}

Where n is the number of teeth (n = 106):

\text{Indexing} = \frac{40}{2} = 20

So, no full turns and 20 holes on the 53-hole circle.

Step 5

5.3 Calculate the depth of the screw thread

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Answer

Using the given hint, the depth of the screw thread can be calculated as follows:

ext{Depth} = 0.866 P

Given P = 2 mm:

ext{Depth} = 0.866 \times 2 = 1.732 \, ext{mm} (approximately \, 1.73 \, mm)

Step 6

5.4.1 Addendum

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Answer

The addendum is equal to the module (m):

ext{Addendum} = m = 3 \, ext{mm}

Step 7

5.4.2 Dedendum

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Answer

The dedendum can be calculated using the formula:

ext{Dedendum} = 1.157 m

Substituting the module:

ext{Dedendum} = 1.157 \times 3 = 3.471 \text{ mm} (approximately \, 3.47 \, mm)

Step 8

5.4.3 Clearance

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Answer

Clearance is given by:

ext{Clearance} = 0.157 m

Substituting the module:

ext{Clearance} = 0.157 \times 3 = 0.471 \, ext{mm} (approximately \, 0.47 \, mm)

Step 9

5.4.4 Pitch-circle diameter (PCD)

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Answer

The pitch-circle diameter can be calculated by:

ext{PCD} = m \times T

Where T is the number of teeth:

ext{PCD} = 3 \times 48 = 144 \, ext{mm}

Step 10

5.4.5 Outside diameter

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Answer

The outside diameter is calculated with:

ext{OD} = PCD + 2m

Substituting the values:

ext{OD} = 144 + 2 \times 3 = 150 \, ext{mm}

Step 11

5.4.6 Cutting depth

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Answer

The cutting depth can be determined as:

ext{Cutting depth} = 2.157 m \, (or \, 2.25 \, mm)

Both values can be used depending on the context.

Step 12

5.4.7 Circular pitch

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Answer

The circular pitch is calculated by:

ext{Circular pitch} = m \times \pi

Using the module:

ext{Circular pitch} = 3 \times \pi \approx 9.42 \, ext{mm}

Step 13

5.5 Identify the type of key shown in FIGURE 5.5

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Answer

The type of key shown in Figure 5.5 can be identified as a parallel key, Pratt and Whitney key, or feather key.

Step 14

5.6 Identify the milling process shown in FIGURE 5.6

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The milling process shown in Figure 5.6 is identified as straddle milling.

Step 15

5.7 Identify the engineering equipment shown in FIGURE 5.7

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The engineering equipment shown in Figure 5.7 is identified as a milling machine (universal or vertical/horizontal milling machine).

5.1 A parallel key must be machined to fit onto an 84 mm diameter shaft - NSC Mechanical Technology Fitting and Machining - Question 5 - 2018 - Paper 1

Worked Solution & Example Answer:5.1 A parallel key must be machined to fit onto an 84 mm diameter shaft - NSC Mechanical Technology Fitting and Machining - Question 5 - 2018 - Paper 1

5.1.1 The width of the key

5.1.2 The thickness of the key

5.1.3 The length of the key

5.2 Calculate the simple indexing

5.3 Calculate the depth of the screw thread

5.4.1 Addendum

5.4.2 Dedendum

5.4.3 Clearance

5.4.4 Pitch-circle diameter (PCD)

5.4.5 Outside diameter

5.4.6 Cutting depth

5.4.7 Circular pitch

5.5 Identify the type of key shown in FIGURE 5.5

5.6 Identify the milling process shown in FIGURE 5.6

5.7 Identify the engineering equipment shown in FIGURE 5.7

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