machinedrawingViva.md

#FASTENERS

• What is fastening? Types of fastening? Use of each type?

  • A fastener is a hardware device that mechanically joins or affixes two or more objects together.
  • Temporary and Permanent. Permanent is used when it has to be joint permanently without any scope of disconnecting two components.

• What are two basic types of threads? Where each type is used?

  • External and Internal. External on bolts , studs etc and internal on nuts , components etc.

• Define the terms : fundamental triangles , truncation , depth of thread , pitch , lead , slope, flank , thread angle , crest ,root , and axis of thread.

What are left handed and right handed screw threads ?

• If keeping a nut bolt in left hand rotating it clockwise using right hand advances the bolt into the nut then it has right handed screw thread.

• What is a helix and a pitch of helix?

  • The path formed when a threaded bolt advances is called helix. Pitch of a helix is the width of one complete helix turn.

• Which type of thread is used for power transmission or load lifting?

  • Square thread as they offer less resistance and friction to relative rotation.

• What is a single start thread?

  • For a single start thread , only one thread follows up and hence making pitch = lead

• What are pitch ,slope and lead in case of double start thread?

  • Pitch = P, lead = P*2, slope = lead/2= P

• What are multi start thread?

  • 2 or more ridges on the cylinder.

• What is a through bolt , a tap bolt ,a stud bolt? Use of each ?

  • Bolt is a threaded cylinder with a head.

• When a bolt passes through one part and is screwed to internal threading of other , it is a tap bolt.

• Stud bolt is a cylinder with opposite handed threading on both sides and hence no head. It is used to connect two components and doesn't pass through them but just connects internally.

• What is an eye bolt?

  • It is a screw with an eye (loop/hook) at top. It is used to clamp or lift loads which are attached via a cable.

• What is a set screw?

  • Set screw is a semi temporary screw to join one component inside of other. It is used to secure a gear to a shaft or so.

• Why a nut of a bolt chamfered?

• It is chamfered to make ensure safety of user and make it easier to join.

• What are locking devices?

  • Sometimes due to vibrations, a nut may get loose and hence unfasten. This is dangerous for the machinery and to prevent this some locking devices are used.

• Lock nut :First lock nut is tightened and then the main nut is screwed down and fastened tightly so that the threading of lock nut gets wedged with that of bolt, hence locking main nut from slacking.

• Spring Washer : It is a friction locking device , due to spring action it locks it and tightens the threads of nut against of bolt.

• Split pin :This is cheap solution yet very safe. We drill a hole into nut and bolt and add split pin to lock it. Disadvantage is that if we remove the nut then aligning the holes again is not easy and also that holes weaken the strength. Castle nut or a slotted nut is used sometimes , however aligning the slot and hole gets difficult.

• What are foundation bolts and where are they used?

  • To fix heavy machinery to concrete foundation, foundation bolts are used. They are often cemented but sometimes molten sulphur is used for quick setting.

• How are threads cut? Taps for internal, die for external

• What are different types of Square threads for fastening?

  • Square thread,Acme thread,Buttress thread,knuckle thread.

KEYS , PINS AND JOINTS

• What is a gib? Where and why is it used? How it is installed in a place?

  • Gib is a mild steel piece (wedge) used to hold pieces together. It is used in gib and cotter joint for 2 reasons :

    • 1. To stop cotter from moving and being lose.
    • 2. To the bearing area of contact.

• Why it is necessary to include some clearances in cotter joints?

  • So that adjustments can be made while inserting it. Clearances between the cotter and slots in the rod end and socket allows the driven cotter to draw together the two parts of the joint until the socket end comes in contact with the cotter on the rod end.

• Under what circumstances cotter joints are used?

  • Used where parts are subjected to axial forces only.

• What is difference between cotter joint and pin joint?

  • Pin allows radial movement, cotter doesn’t. Both do block axial forces however knuckle is used only for tensile axial force however cotter can even handle compression.

• Comparison between key and cotter?

  • Keys are driven in parallel to shaft axes and subjected to torsional and twisting stress.

• Cotters are driven at right angles and subjected to tensile or compressive stress. It can resist shear force in two traverse directions.

• Why a head is made at one end of gibhead key?

  • So that it is easy to remove it. It will not be possible to insert it if it will have twoheads.

• What is the usual taper provided onface of sunk key?

  • 1 in 100

• What is the difference between sunk and saddle key?

  • Half in shaft (key seat), half in hub(keyway) – sunk through a key way , used for heavy duty. Saddle is flat and used for light duty (usually tapered).

• What is a cotter?

  • A cotter is a flat wedge-shaped piece of steel. This is used to connect rigidly two rods which transmit motion in the axial direction, without rotation. These joints maybe subjected to tensile or compressive forces along the axes of the rods.

• What type of joint you would recommend for shafts whose axes don't lie in straight line?

  • Oldham joint (parallel) / Universal Joint (at angle).
  • SHAFT COUPLINGS

• Difference between rigid and nonrigid shaft couplings?

  • Rigid :They connect shafts in rigid alignment , hence no deviations in axes or angle is tolerated. Flange , muff , compression etc.

  • Non Rigid :Allow slight angular deviations or shift in axes. : Oldham , pin type flexible, universal coupling.

• Why are split muff couplings used in preference to solid muff?In solid muff , in order to couple the shafts , one has to move either one of shaft endwise. This may not be always possible, hence we use split muff coupling where one key is used and the muff is divided in two parts and then connected.

• What is spigot and socket centering as applied to flange couplings?

  • An outstanding cylindrical portion is used in one flange called spigot or register and corresponding recess in the mating flange is used to register that spigot.This helps in centring the spigot and socket and maintains aligment.

  • Two shafts are to be connected together in line. It should 1) be possible to disconnect without disturbing 2)not have projecting pieces which may cause injury.

  • Protected flange coupling as they have overhanging projections on nut and bolts so that they don’t get caught by cloth or fingers of workers and hence protect them. To dismantle the flanges , we just have to unscrew the bolts.

• Under what circumstances oldham coupling can be used?

  • Shafts not in same line.

• What is the specific use of expansion joint?

  • Allows angular deviation.

BEARINGS

• What is the function of a bearing?

  • Rotating shafts are supported on bearings. Their role is to minimize friction during rotating and also reduce heating and seizing.

• What is a journal? Type of bearings (3)?

• Journal is part of shaft near bearing body.

• Journal, pivot or footstep, thrust.

• Perpendicular to axis,parallel to axis,parallel but with thrust end.

• Why lubrication is required?

  • To prevent seizing of shaft and heat generation.

• Whatis seizing of shafts?

  • When a shaft gets stuck in the bearing, it get seized and eventually gets cracks.

• How to prevent metal to metal contact? Brasses and bushes

• Why a bush is provided in between the shaft and body of bearing? What material of bush is used? It is provided to reduce rotational friction and facilitate the rotation of shaft. We could have used integral hole and move the shaft there , but since bushes are made of cheap material and can be easily replaced , whereas the integral hole once worn , would require to replace entire base , we hence use bushes.

  • Material : brass , gunmetal ,phosphor bronze or manganese bronze.

• Why the rotation of brasses with shaft is to be prevented? If it moves then it will cause obstruction in proper rotation and will also damage the base. Thus bushes are not at all meant for rotation. They are blocked by use of snug or collar.

• What is pivot bearing?

  • Footstep bearing, used for vertical shaft. It has a pad inside it which is blocked from rotation using a snug dug into the sole.

• Difference between footstep and journal bearing?

  • Journal is for load connected perpendicular to axis and footstep is for load connected parallel to axis.

• Why a pad or disc provided below shaft end in a pivot bearing?

  • It is a sacrificing component , it is easily removed when worn out. It protects the sole which can not be replaced if once worn.

• When is an angle plummer block used?

  • To transmit power at an angle.

• What is a snug?

  • In order to stop brasses from rotating or move axially , we use snug into a recess in the sole.

• Why the split bearings are preferred over solid bearing?

  • Solid bearings can only be used if the shaft is inserted endwise. Hence split bearings are used to use it anywhere along the shaft.

• Why clearance is given between cap of plummer block and body?

  • To provide smooth seat to nuts. It gives an allowance for some movement due to thermal changes.

• Why collars are provided at sides of brasses?

  • To prevent axial motion of the brasses.

• What is the advantage of swivel bearing?

• What are different methods of lubricating the bearing?

• Various conventions were asked to draw.

• What is the relation between the diameter of rivet and the thickness of a plate when two plates are joined.

  • Explain co-diameter.

External

• Name different parts of Foot-Step Bearing ?
• Which type of bearing is used in foot-step bearing ?
• State one application of Acme Thread.
• What is the use of snug ?
• What are the types of bearings?
• Types of threads? Their classification?
• Applications of Knuckle joint, Universal coupling ?
• What is a rivet? What are their commercial applications?
• What kind of material are bolts, bearings, etc. made of?
• What is the most prominent property of above mentioned material?
• How do you seal or hold a rivet in place after inserting it in the requisite position? Why is said method of sealing a better idea than simply securing the rivet with nuts?
• What property of rivets and studs is significant in their application of joining metal sheets together?
• Draw the section of a solid flange. What kinds of flanges and couplings can function without keys?
• What's the difference between a stud and a rivet?
• Draw 1st angle,3rd angle symbol
• Is it possible to make drawings in 2nd angle
• What are rivets?Draw 5 type of rivets.
• What is Lap joint?Butt joint?Draw their diagrams(Both chain and zig-zag)
• An example of butt joint.
• Application of knuckle thread.
• Example of rivets in daily life and in college.