5.1 A parallel key must be machined to fit onto a 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 Basic calculations: 5.1 A parallel key must be machi

5.1 A parallel key must be machined to fit onto a 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 a 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 T... show full transcript

Worked Solution & Example Answer:5.1 A parallel key must be machined to fit onto a 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

The width of the key can be calculated using the formula:

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

Where D is the diameter of the shaft. Thus, substituting the values:

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 given by the formula:

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

Substituting for D:

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 found using:

ext{Length} = D \times 1.5

Substituting the diameter:

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

Step 4

5.2 The simple indexing needed

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Answer

Simple indexing can be calculated as follows:

ext{Indexing} = \frac{40}{n} ext{ where } n = 106 ext{ teeth}

Calculating it gives:

ext{Indexing} = \frac{40}{2} = 20 ext{ holes on the 53-hole circle.}

No full turns are required.

Step 5

5.3 The depth of the screw thread

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Answer

The depth of the screw thread can be calculated using the provided hint:

ext{Depth} = 0.866P

Where P is the pitch (2 mm):

ext{Depth} = 0.866 \times 2 = 1.73 ext{ mm}

Step 6

5.4.1 Addendum

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Answer

The addendum is equal to the module:

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

Step 7

5.4.2 Dedendum

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Answer

The dedendum is calculated as follows:

ext{Dedendum} = 1.157m

Substituting the module:

ext{Dedendum} = 1.157 \times 3 = 3.471 ext{ mm}

Step 8

5.4.3 Clearance

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Answer

Clearance is given by the formula:

ext{Clearance} = 0.157m

Calculating it:

ext{Clearance} = 0.157 \times 3 = 0.471 ext{ mm}

Step 9

5.4.4 Pitch-circle diameter (PCD)

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Answer

The pitch-circle diameter can be calculated:

ext{PCD} = m \times T

Where T is the number of teeth (48):

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 as:

OD = PCD + 2m

Substituting the values:

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 calculated as:

ext{Cutting depth} = 2.157m ext{ or } 2.25m

Calculating gives:

ext{Cutting depth} = 2.157 \times 3 = 6.471 ext{ mm}

Step 12

5.4.7 Circular pitch

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Answer

The circular pitch is given by the formula:

ext{Circular pitch} = m \times \pi

Calculating it out:

ext{Circular pitch} = 3 \times \pi \approx 9.43 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 is a Parallel key, or it could also be a Pratt and Whitney key or a Feather key.

Step 14

5.6 Identify the milling process shown in FIGURE 5.6

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Answer

The milling process shown 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 is a Milling machine, which may be universal or horizontal.

5.1 A parallel key must be machined to fit onto a 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 a 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 The simple indexing needed

5.3 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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