Fixtures And Jigs

Definition Of Fixture And
Jig:

Fixtures, being used in machine
shop, are strong and rigid mechanical devices which enable easy, quick and
consistently accurate locating, supporting and clamping, blanks against cutting
tools and result faster and accurate machining with consistent quality,
functional ability and interchangeability.

                         

Jig is a fixture
with an additional feature of tool guidance.

 Purpose Of Using
Fixtures And Jigs:-
conventional drilling
machine without using any fixture or jig, the following elementary steps are to
be sequentially followed
  1.   cleaning and deburring
    the blank (disc) 
  2.   marking on the blank
    showing the location of the hole and its axis on the blank
  3.   punch the centre at the
    desired location and prick punch the periphery of the hole to be made in
    the disc
  4.   mount the blank in a
    drilling vice using parallel block, a small Vee block etc. to provide
    support and clamp the blank firmly
  5.   position the vice along
    with the marked blank to bring the hole axis in alignment with the drill
    axis by 
  •  either adjusting the vise
    position w.r.t. the fixed drill axis 
  •  or moving the drilling
    machine table and then locking the table position 
  •  or moving the radial arm
    and the drilling head, if it is a radial drilling machine 
6.   after
fixing the blank, vise and the table, alignment is checked again
7.  if error, like
eccentricity, is found to occur then readjustment of location of the hole –
axis is to be done before and even after starting drilling
 8.  drilling
is accomplished.
The basic purposes of
developing and using suitable jigs and fixtures for batch production in machine
shops are :-
1.  to eliminate
marking, punching, positioning, alignments etc. 
2. easy, quick and
consistently accurate locating, supporting and clamping the blank in alignment
of the cutting tool 
3. guidance to the
cutting tool like drill, reamer etc. 
4. increase in
productivity and maintain product quality consistently 
5. to reduce
operator’s labour and skill – requirement 
6. to reduce
measurement and its cost 
7. enhancing
technological capacity of the machine tools 
8. reduction of
overall machining cost and also increase in interchangeability.
 
Jigs and fixtures are
manually or partially power operated devices. To fulfil their basic purposes,
jigs and fixtures are comprised of several elements:
1.  base and body or
frame with clamping features 
2. locating elements
for proper positioning and orientation of the blank 
3. supporting
surfaces and base 
4. clamping
elements 
5. tool guiding frame
and bushes (for jig) 
6. indexing plates or
systems, if necessary 
7. auxiliary
elements 
8. fastening
parts 

  

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