6.1 A machinist in a milling workshop is tasked to cut a spur gear with 180 teeth and a module of 2.5. Calculate the following: 6.1.1 Pitch-circle diameter 6.1.2 Dedendum 6.1.3 Outside diameter 6.2 FIGURE 6.2 below shows an external dovetail component for a machine vice. Calculate the following: 6.2.1 Maximum width (W) distance of the dovetail 6.2.2 Distance (m) between the precision rollers 6.3 A spur gear with 89 teeth must be cut on a milling machine with the use of a dividing head. The dividing head has a ratio of 40 : 1. HINT: Use A = 90 divisions for the simple indexing. 6.3.1 Calculate the indexing that is needed. 6.3.2 Calculate the change gears that are required. 6.4 Describe any TWO constraints/disadvantages that can be experienced during the practical application of balancing a work piece on a lathe when using a weight.

NSC Mechanical Technology Fitting and Machining Mechanical components: 6.1 A machinist in a milling wor

6.1 A machinist in a milling workshop is tasked to cut a spur gear with 180 teeth and a module of 2.5 - NSC Mechanical Technology Fitting and Machining - Question 6 - 2023 - Paper 1

Question 6

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6.1 A machinist in a milling workshop is tasked to cut a spur gear with 180 teeth and a module of 2.5. Calculate the following: 6.1.1 Pitch-circle diameter 6.1.2 De... show full transcript

Worked Solution & Example Answer:6.1 A machinist in a milling workshop is tasked to cut a spur gear with 180 teeth and a module of 2.5 - NSC Mechanical Technology Fitting and Machining - Question 6 - 2023 - Paper 1

Step 1

6.1.1 Pitch-circle diameter

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Answer

To calculate the pitch-circle diameter (PCD) of the spur gear, use the formula:

PCD = m \times T

Where:

$m$ = module = 2.5
$T$ = number of teeth = 180

Calculating gives:

PCD = 2.5 \times 180 = 450 \text{ mm}

Step 2

6.1.2 Dedendum

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Answer

The dedendum can be calculated using the formula:

Dedendum = 1.157 \times m

Substituting the known values:

Dedendum = 1.157 \times 2.5 = 2.89 \text{ mm}

Step 3

6.1.3 Outside diameter

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The outside diameter (OD) of the spur gear can be calculated using:

OD = PCD + 2 \times m

Substituting the values:

OD = 450 + 2 \times 2.5 = 455 \text{ mm}

Step 4

6.2.1 Maximum width (W) distance of the dovetail

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Answer

To find the maximum width (W), first calculate DE using tangent geometry:

\tan \theta = \frac{DE}{AD}

Given $AD = 50$ :

DE = \tan 60^{\circ} \times 50 \approx 28.87 \text{ mm}

Then:

W = 136 + 2(28.87) = 193.74 \text{ mm}

Step 5

6.2.2 Distance (m) between the precision rollers

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Calculate distance (m) using:

m = W - 2(AC + R)

With $AC = 17.32$ and radius $R = 10$ :

m = 193.74 - 2(17.32 + 10) ightarrow m \approx 139.10 \text{ mm}

Step 6

6.3.1 Calculate the indexing that is needed

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Answer

For the indexing required, use:

Indexing = \frac{40}{N} = \frac{40}{89} \times 40 = 24

This means 0 full turns and 24 holes on a 54-hole circle.

Step 7

6.3.2 Calculate the change gears that are required

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Change gears can be calculated using:

\frac{D_r}{D_n} = \frac{(A - n) \times 40}{A}

For our scenario, where $A = 90$ :

This gives:

D_r : D_n = 4 : 9 ext{ or } D_r = 32, D_n = 72

Step 8

6.4 Describe any TWO constraints/disadvantages

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Requires specialized machinery: Balancing needs tools and machines specifically designed for the purpose, which increases operational costs.
Difficult to ascertain the exact point of unbalance: Achieving precise balance requires detailed knowledge of the workpiece and operational parameters, making it complex during the balancing process.

6.1 A machinist in a milling workshop is tasked to cut a spur gear with 180 teeth and a module of 2.5 - NSC Mechanical Technology Fitting and Machining - Question 6 - 2023 - Paper 1

Worked Solution & Example Answer:6.1 A machinist in a milling workshop is tasked to cut a spur gear with 180 teeth and a module of 2.5 - NSC Mechanical Technology Fitting and Machining - Question 6 - 2023 - Paper 1

6.1.1 Pitch-circle diameter

6.1.2 Dedendum

6.1.3 Outside diameter

6.2.1 Maximum width (W) distance of the dovetail

6.2.2 Distance (m) between the precision rollers

6.3.1 Calculate the indexing that is needed

6.3.2 Calculate the change gears that are required

6.4 Describe any TWO constraints/disadvantages

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