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EXPERIMENT No. 8

Aim: To determine Mechanical Advantage, V.R. and Efficiency of worm and worm gear of single, double and triple start.

Apparatus: Worm and worm gear of single, double and triple start and weights.

Theory: As the pulley of the worm moves through n revolutions, n teeth of the wheel pass completely through theworm. If there are N teeth in the worm wheel, then N revolutions will have to be given to the pulley of the worm to

rotate completely the worm wheel. So that if the effort applied at the pulley of the worm moves through N

revolution the load is raised up by the a distance equal to the length of the circumference of the pulley of the worm

wheel.

So that velocity ratio is

N x circumference of pulley of worm

Circumference of pulley of worm wheel

Procedure:

1. Wrap the string round the pulley of the worm the free end of which is to be tied to the effort.2. Wrap another string to carry the load round the pulley the worm wheel in such a manner that as the effort is

applied the load is lifted up.

3. Suspend a small weight (w) through the free end of the second string and suspend another weight (p) through

the free end of the first string which should just move the load upward.

4. Note w and P, so that mechanical advantage is given by W/ P

5. Increase the load (w) gradually and increase the effort (p) correspondingly andtake in this way about seven readings.6. Measure the circumference of the pulley of the worm and also that of the worm wheel.

7. The percentage efficiency is given by W x 100 /PV

8. Plot a graph between w and p.

9. The same procedure can be followed for single, double and triple start worm and worm wheel.

Observations :

1. Circumference of pulley of the worm (2R1) = _________ cm.

2. Circumference of pulley ofthe worm wheel (2R2) =_________ cm.

http://4.bp.blogspot.com/-qBQC6dpE8Q0/TvAY7iz_aYI/AAAAAAAAAFE/4aSVBktcKWU/s1600/fig.bmp

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3. No of teeth in the worm wheel (N)=

4. Velocity ratio for single start= (N x 2R1)/((2R2)*1)

5. Velocity ratio for double start= (N x 2R1)/((2R2)*2)

6. Velocity ratio for triple start= (N x 2R1)/((2R2)*3)

Observations Table for single start:

S. No. Weight Lifted(W)

Effort Applied(P)

Mech. Adv. =W/P

VelocityRatio

% Efficiency=W/PV x 100

1

2

3

4

5

6

Observations Table for double start:

S. No. Weight Lifted

(W)

Effort Applied

(P)

Mech. Adv. =

W/P

Velocity

Ratio

% Efficiency

=W/PV x 100

1

23

4

5

6

Observations Table for triple start:

S. No. Weight Lifted

(W)

Effort Applied

(P)

Mech. Adv. =

W/P

Velocity

Ratio

% Efficiency

=W/PV x 100

1

2

3

4

5

6

Conclusion: Hence the efficiency of single, double and triple worm and worm wheel is completed.