class test 4 & 5 cams _ gears - assignment questions kom (1)

7/25/2019 Class Test 4 & 5 Cams _ Gears - Assignment Questions Kom (1)

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MLRINSTITUTE OF TECHNOLOGYLaxma Reddy Avenue, Dundigal, Hydea!ad " #$$ $%&

CLASS TEST %' DATE(UNIT %) CAMS *O+ECTI-E .UESTIONS/' ROLL NO'

1. For the knife edge follower, the cam prole and pitch curve [ +]A) are dierent B)are ame !)ma" #e ame or dierent $)none of the a#ove

%. &he angle, which repreent the cam prole and i mot important in cam deign, +]

A) Cam angle B) pressure angle C) angle of dwell D) angle of descent

3. The Size of a cam depends upon [ A]'A) Bae circle 'B) (itch circle '!) (rime circle '$) (itch curve

. &he cam follower generall" ued in automo#ile engine i [C]'A) *nife edge follower 'B) Flat faced follower '!) +pherical faced follower '$) ollefollower

-. &he troke of the follower i eual to /////// [+]'A) 0alf of the maimum travel of the follower from the lowet poition &o the tomot poition

'B) 2aimum travel of the follower from the lowet poition to the top mot poitionC) !alf of the diameter of "ase circle D) !alf of the diameter of prime circle

#. A radial follower is one which [ A]A )translates along an a$is passing through the cam centre

B) reciprocates in guides

C) oscillates with a simple harmonic motionD) has an a$is of mo%ement displaced from the a$is of rotation of cam.

3. $uring the dwell period of a cam, the follower move [ D]A) &ith uniform speed B) &ith Simple harmonic motion C) 'n a straight line

D) (emains at rest

FILL IN THE BLANKS. The lift of a flat*faced follower+ when it is in contact with the flan, of a circular arc cam+is e-ual to [(R

r1)(1-cos)]0) &he cam and follower i an eample of Hig1e 2ai4. 5n a radial cam, the follower move in a direction 3e2endi4ula to the cam ai. &he angle, which repreent the cam prole and i mot important in cam $eign

3e55ue angle.-. &he period during which follower remain tationar" during ome nite rotation

the !am i D6ell 3ei7d .#. The cam size depends upon Base circle.

7. or low and moderate speed engines+ the cam follower should mo%e with Simpe !armo"ic mo#io"

$. &hen the follower mo%es with S!/+ the %elocit0 diagram is Si"%soi&a cur%e'. The size of a cam depends on ase circe1. The angle "etween the direction of the follower motion and a normal to the pitch cur%e

called press%re a"*e

11. The retardation of a flat faced follower when it has contact at the ape$ of the nose of circular arc cam+ is gi%en "0 (+ , /) where 12 is the distance "etween the centres of "ase nose circles.

4. or high speed engines+ the cam follower should mo%e with c0coi&a mo#io"

1. 1ffset is pro%ided to a cam follower mechanism to mi"imi2e #!e si&e #!r%s#


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MLRINSTITUTE OF TECHNOLOGY

Laxma Reddy Avenue, Dundigal, Hydea!ad " #$$ $%&CLASS TEST #' DATE'3NIT 4. HI5HER 6AIES 5EAR TRAINS RLL N8

. The motion transmitted "etween the teeth of two spur gears is generall0 [9]A) sliding B) rolling C)rotar0 D)partl0 sliding and partl0 rolling

4. &hich of the following represents the locus of the common point on the two meshing gears5[:]

a) addendum circle ") root circle c) pitch circle d) "ase circle

3. 6aw of 7earing is satisfied if [ :]A) Two surfaces slide smoothl0 B) no. of teeth 8 9CD : module

C) Common normal at the point of contact passes through pitch point on the line ;oining the centers

rotationD) Addendum is greater than Dedendum


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@. 'f the module of a gear "e m+ the num"er of teeth T and pitch circle diameterD+ then module m) is gi%en "m


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4Q: What are the different motions of the follower

Ans:

(i) Uniform motion

(ii) Simple harmonic

(iii) Uniform acceleration and retardation

(iv) Cycloidal motion.

5Q: Distinguish radial cam and cylindrical cam.

Ans:

Radial cam Cylindrical cam

1. In this cam, the follower reciprocates

(or) oscillates in a direction

perpendicular to the cam axis.

1. In this the follower reciprocates (or)

oscillates in a direction parallel to the cam

axis.

6Q: Define undercutting CAM.

Ans:

If the curvature of the pitch curve is too sharp, then the part of the cam shape would be lost an

thereafter the intended cam motion would not be achieved. Such a cam is said to be undercut.

Undercutting in cam profile be avoided

(i) By decreasing the desired follower lift, L

(ii) By increasing the cam rotation angle, and

(iii) By increasing the cam size.


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7Q: Compare Roller and Mushroom follower.

Ans:

Roller follower Mushroom follower

1. Roller followers are extensively used

where more space is available.

2. It is used in stationary, gas engines,

oil engine and aircraft valves in engines.

1. The mushroom followers are

generally used where space is limited.

2. It is used in cams which operate the

valves in automobile engines.

The roller follower extensively used

Roller followers are extensively used where more space is available such as in stationary gas o

engines and air craft engines.

8Q: Classification of Cams:

Ans:

1. Radial or disc cam:

In radial cams, to follower reciprocates or oscillates in a direction perpendicular to cam axis. Th

Cams as shown in Fig are all radial cams.

2. Cylindrical cam:

In cylindrical cams, to follower reciprocates or oscillates in a direction parallel to the cam ax

The follower rides in a groove at its cylindrical surface.

9Q: Classify the Followers according to surface in contact.

According to the surface in contact. The followers, according to the surface in contact are as Follows:

(a) Knife edge follower :

When the contacting end of the follower has a sharp knife edge, it is called a knife edge follower.

(b) Roller follower:


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When the contacting end of the follower is a roller, it is called a roller follower.

(c) Flat faced or mushroom follower:

When the contacting end of the follower in a perfectly flat face, it is called faced follower.

(d) Spherical faced follower:

When to contacting end of the follower is of spherical shape, it is called a spherical faced follower.

10 Q: Define Pressure Angle, Pitch Point, Pitch Circle, Pitch Curve, Prime Circle & Lift of the CAM

Ans:

Pressure angle:

It is the angle between the direction of to follower motion end a normal to the pitch curv

The angle is very important in designing a Cam profile. It to pressure angle is too large a reciprocatin

follower will jam in its bearing.

Pitch point: It is a point on the pitch curve having to maximum pressure angle.

Pitch Circle: It is a circle drawn from the centre of the Cam through to pitch point.

Pitch curve: It is the curve generated by the trace point as the follower moves relative to the Cam. Fo

Knife edge follower, the pitch curve and the Cam profile are same where as for a roller follower they a

separated by to radius of the roller.

Prime Circle: It is the smallest circle that can be drawn from the centre of the Cam and tangent to th

pitch curve. For a Knife edge and a flat face follower, the prime circle and the base circle are identica

For a roller, follower, to prime circle is larger than to base circle by the radius of the roller.

Lift or stroke: It is the maximum travel of the follower from its lowest position to the top mo

position.


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ASSI5NENT /3ESTINSC 3NIT 4C HI5HER 6AIRS 5EAR TRAINS

1Q:What are the advantages & limitations of the Gears?

Ans:

The advantages of Gear drive.

Exact velocity ratio is obtained, since there is no slip.

It is capable of transmitting larger power than that of the belt and chain drives.

It is more efficient and effective means of power transmission.

It requires less space compared to belt and rope drives.

The limitations of gear drive.

The manufacture of gear requires special tools and equipments.

The manufacturing cost is comparatively high.

The error in cutting teeth may cause vibrations and noise during operation.

2Q:Classify gears?

Ans:

a. Based on the position of teeth on the wheel:

(i) Straight gears (ii) Helical gears (iii) Heringbone gears (iv) Curved teeth gears.

b. Based on peripheral speed: (v)

(i) Low velocity V < 3 m/s (ii) Medium velocity gears V = 3 to 15 m/s

(iii) High velocity gears V > 15 m/s.

c. Based on the relative of the shafts

(i) Row gears (ii) Planetary gears.


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3Q:Define path of contact, arc of contact, arc of approach and arc of recess

Ans:

path of contact.

It is the path traced by the point of contact of two teeth from the beginning to the end

engagement.

arc of contact

It is the path traced by a point on the pitch circle from the beginning to the end of engagement

a given pair of teeth.

arc of approach

It is the portion of the path of contact from the beginning of the engagement to the pitch point.

arc of recess

It is the portion of the path of contact from the pitch point to the end of the engagement of a pa

of teeth.

4Q:Define Addendum Circle, Addendum, Deddendum Circle, Clearance and Backlash in gears.

Ans:

Addendum circle.

It is the circle drawn through the top of the teeth and is concentric with the pitch circle.

Addendum.

It is the radial distance of a tooth from the pitch circle to the top of the tooth.

Deddendum circle.

It is the circle drawn through the bottom of the tooth and is concentric with the pitch circle.

Clearance with reference to the terminology of gears.


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It is the radial distance from the top of the tooth to the bottom of the tooth, in a meshing gear.

Backlash in gears.

It is the difference between the tooth space and the tooth thickness along the pitch circle.

Backlash = Tooth Tooth thickness.

5Q:Define Circular Pitch, Diametral Pitch and Module with reference to gears.

Ans:

Circular Pitch

It is the distance measured along the circumference of the pitch circle from a point on one tooto the corresponding point on the adjacent tooth.

PC=T

D

D = Diameter of pitch circle,

T = No of teeth on the wheel.

Diametral Pitch in reference to gears.

It is the ratio of number of teeth to the pitch circle diameter.

Pd=D

T

T = No of teeth

D = Pitch circle diameter

Relationship between Diametral pitch and circular pitch.

Pd=C9

Pd= Diametral pitch

PC= Circular pitch.


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Module

It is the ratio of the pitch circle diameter to the number of teeth.

m =

T

D

6Q;State the law of gearing.

Ans:

It states that for obtaining constant velocity ratio, at any instant of teeth the common normal

each point of contact should always pass through a pitch point, situated on the line joining the centre

rotation of the pair of making gears.

7Q: Write the differences between involute and cycloidal tooth profile

Ans:

S.No Involute tooth profile Cycloidal tooth profile

Variation in centre distance does not

affect the velocity ration.

The centre distance should not vary.

Pressure angle remains constant

throughout the teeth.

Pressure angle varies. It is zero at

the pitch point and maximum at the

start and end of engagement.

3. Interference occurs No interference occurs

4. Weaker teeth Stronger teeth.

1.

2.

class test 4 & 5 cams _ gears - assignment questions kom (1)

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