BITs edu campus

• Urvesh Dungarani 140050119506• Dharmendra Rathod

140050119505

Lab faculty:-NILESH PATEL

SCREW THREAD• A S C R E W T H R E A D I S A R I D G E O F U N I F O R M S E C T I O N I N

T H E F O R M O F A H E L I X O N T H E E X T E R N A L O R I N T E R N A L S U R F A C E O F A C Y L I N D E R .

• T H E P I T C H O F A T H R E A D P I S T H E D I S T A N C E F R O M A P O I N T O N T H E T H R E A D F O R M T O T H E C O R R E S P O N D I N G P O I N T O N T H E N E X T F O R M , M E A S U R E D P A R A L L E L T O T H E A X I S

ERROR IN MEASUREMENT

• There are at least five important elements which require consideration:

• Major diameter

• Minor diameter

• Effective diameter

• Pitch and angle of the thread form

• Errors on the major and minor diameters will cause interference with the mating thread

• Errors on the effective diameter will also result in weakening of the assembly

• pitch and angle errors are also not desirable as they cause a progressive tightening and

interference on assembly

MAJOR DIAMETER• The major diameter of an internal thread is normally measured by some form of

horizontal comparator fitted with ball ended styli of radius less than the root radius of the

thread to be measured.

• One of the styli is attached to a floating head which is kept in contact with the spindle or

dial indicator.

• The major diameter D can be calculated by

Knowing the value of x as,

D= 𝒙𝟐 − (𝒑

𝟐)𝟐

where p is pitch of the screw thread.

MINOR DIAMETER• When the value of minor diameter is less then 20mm, taper parallels and micrometre are

used for measurement for diameter above 20mm,calibrated roller and slip gauges arc

used.

• Using taper parallel:

• The taper parallel are pair of wedges having reduce and parallel outer edges. the diameter

across their outer edges can be changed by sliding then over each other.

• In this method ,precision rollers are inserted inside the thread and proper slip gauges

inserted the roller as shown in fig.

• The minor diameter is then the length of slip gauges plus twice the diameter of roller.

• Dm =X+2d

• Where, Dm = minor diameter

• X = slip gauges distance

• d = roller diameter.

USING SLIP GAUGES AND ROLLERS

MEASUREMENT OF EFFECTIVE DIAMETER• The effective diameter of internal screw thread is measured using bail-ended styli of

best wire size in thread measuring machine.

• The VEE notches are separated by slip gauges of length X which gives the effective

diameter as follow

• Let, P=pitch and Ø=flank angle

tanØ = p/4z

MEASUREMENT OF PITCH

• Using an adapter, pitch of an internal thread can be measured by any pitch measuring

machine. this adapter carries a fine bar which can be inserted into the ring. The styles

being fitted to the bar end as shown in figure engaging with thread in the usual

manner.

• A special set up on the face plate becomes essential for very large ring.

SCREW THREAD GAUGES

• When a large of component with screw thread are to be produced then measurement

of various element of screw thread will be very expensive and time consuming gauges

are scale less inspection tools at rigid design, which are used to check the dimension

of manufacturing parts.

• They also check the form and relative position of the surface of parts.

• They do not measure the actual size or dimension of parts.

• They are only used to determine whether the inspected part as been made within the

specified limit or not.

CLASSIFICATION OF GAUGES

• Plug screw gauges for internal screw thread

Plug gauges are classified in a different types:

A) Full form GO gauge: this external screw threaded plug gauges of the shown in figure.

B) Effective diameter NO GO gauge : the

effective diameter NO GO gauge is

shown in figure.

C) Minor diameter NO GO gauge : this

is a plain cylindrical plug gauges

manufactured to the high limit of the

minor diameter. This gauges shown in

figure

• For production gauging of bolts, the equivalent mating surface of the bolt threads is

known as a ring gauges. The GO ring gauges is the full form of thread , the NO-GO

gauges being truncated on the minor diameter and clear on the major diameter at the

root of the thread, a GO thread ring gauges is shown in figure.

RING SCREW GAUGES FOR EXTERNAL SCREW THREAD

• Thread snap gauges are far widely used as compared to thread ring gauges which have a

limited field of application. this types of gauges is shown in figure