04 lathe operations
Post on 03-Jun-2018
222 Views
Preview:
TRANSCRIPT
-
8/11/2019 04 Lathe Operations
1/31
Lathe Operations
Dr. N. VENKAIAH
Assistant Professor
Mechanical Engineering DepartmentNIT Warangal !" !!#
Disclaimer
The content presente$ here is not entirel% m% o&n. 'ome portions are ta(en from
$ifferent so)rces &ith great regar$. This content is solel% for class room teaching an$
not for an% commercial )se.
-
8/11/2019 04 Lathe Operations
2/31
Straight Turning
FIGURE : Schematic illustration of a turning operation showingdepth of cut, d, and feed,f. cutting speed is the surface speed
of the workpiece at the tool tip.
-
8/11/2019 04 Lathe Operations
3/31
FacingTool is fed radially inward
-
8/11/2019 04 Lathe Operations
4/31
Contour TurningInstead of feeding the tool parallel to the axis of rotation,
tool follows a contour, thus creating a contoured form
-
8/11/2019 04 Lathe Operations
5/31
ChamferingCutting edge cuts an angle on the corner of the cylinder, forming
a "chamfer"
-
8/11/2019 04 Lathe Operations
6/31
Cut-off
Tool is fed radially into the rotating workto cut off the end of the part
-
8/11/2019 04 Lathe Operations
7/31
Other Operations
Cutting with a form tool
Boring and internal groovingDrilling
Taper turning Knurling
-
8/11/2019 04 Lathe Operations
8/31
Thread Cutting
ointed form tool is fed linearly across surface of rotatingworkpart parallel to axis of rotation at a large feed rate, thuscreating threads
-
8/11/2019 04 Lathe Operations
9/31
Thread Cutting - Terminology
!ig #lements of external threads
!ig #lements of internal threads
It calls fairly high skill on the part of the
operator
Threads are formed on the principle of
helix
Calculation of proper change gears is
crucial
Tool tip should have an included angle
corresponding to the included angle of the
thread to $e produced
The chief elements of all the screw threads%
itch& 'a(or diameter& 'inor diameter& itch
diameter& Depth of threads& Thread angle
-
8/11/2019 04 Lathe Operations
10/31
Thread Cutting Terminology
!ig )ingle )tart
!ig Dou$le )tart
'tart of threa$*
Denotes the num$er of separate thread grovesrunning parallel to each other along the surface of
the screw
A$+antage m)ltiple start threa$s
To o$tain more axial advancement for the same
amount of rotation of the screw as compared to
single start threads without weakening the thread
If the pitch in $oth cases remains the same, the
axial advancement for the same amount of rotation
will $ecome as many times of the single start as
the num$er of starts
The axial advancement in one rotation of the
screw is known as lea$ of the threa$. *hich is the
distance $etween two corresponding points on the
thread measured parallel to the axis,
+ote% Thelea$ scre& of a lathe is al&a%s single
starte$.LeadPitch =No. of Starts
-
8/11/2019 04 Lathe Operations
11/31
Cutting R.H. and L.H. Threads
Right Hand threads:- hreads slope up to the right when
screw is held !erticall".
- o cut R.H. hreads, headstock spindle
and the lead screw should rotate in the
same direction.
#eft Hand threads:- hreads slope up to the left when
screw is held !erticall".- he spindle and the lead screw will
rotate in opposite direction.
This change of direction of rotation on
lathe is effected by tumbler gears or byusin ro er number o idlers.
!igure% ./ Threads
!igure% 0/ Threads
-
8/11/2019 04 Lathe Operations
12/31
Left Hand thread - pplications
-
8/11/2019 04 Lathe Operations
13/31
-
8/11/2019 04 Lathe Operations
14/31
-
8/11/2019 04 Lathe Operations
15/31
Thread Cutting !ear Trains
)imple gear train
Compound gear train
Intermediate gear has no effect on the
change gear ratio It simply acts as a
connection $etween the two, and
serves to keep the rotation of driver
and driven in the same direction
In a compound gear train, the stud
carries two wheels which are keyedtogether so that they rotate as a unit
Compound gear train is employed
when the gear ratio is not possi$le to
o$tain with a simple gear train out of the
given set of change gears
In modern lathes, ;uick change gears
are availa$le to o$tain the correct gear
ratio to cut a particular thread ;uickly
$y simply shifting the lever into different
positions which are marked on theinstruction plates of the machine
-
8/11/2019 04 Lathe Operations
16/31
Cutting metric thread on
"nglish standard lead scre#s or $ice $ersa
o cut metric threads on lathes ha!ing $ritish
standard lead screw:
o cut $ritish standard threads on a lathe
ha!ing lead screw of metric pitch:
-
8/11/2019 04 Lathe Operations
17/31
-
8/11/2019 04 Lathe Operations
18/31
E%ercise
&. 'alculate change gears for cutting R.H. threads of ( mm pitch
on a lathe ha!ing lead screw of ) mm pitch.
Soln.:
0ike this, we can have num$er of solutions
and every solution will give the desired result
-
8/11/2019 04 Lathe Operations
19/31
-
8/11/2019 04 Lathe Operations
20/31
E%ercise *. 'alculate change gears for cutting R.H.$.S.-. /0 threads of
&( 1I on a lathe ha!ing lead screw of 2 1I.
Soln.: 1Driver TPI of Screw to be cutChange gear ratio = =1Driven
TPI of Lead screw
TPI of lead screw=TPI of screw to be cut
8
1 != =
-
8/11/2019 04 Lathe Operations
21/31
E%ercise *3. 'alculate change gears for cutting R.H. threads of & mm pitch
on a lathe ha!ing lead screw of 2 mm pitch.
Soln.:
)uch a ratio with a gear of 3 ? 78& 1ear B ? @8&
and
1ear C ? A8& 1ear D ?
-
8/11/2019 04 Lathe Operations
22/31
E%ercise *+. 'alculate change gears to cut #.H. threads of (+ 1I on a lathe
ha!ing lead screw of ) 1I.
Soln.:
Compound 1ear Train with oneidler%
1ear > ? 8& 1ear B ? 388&
and
1ear C ? 9& 1ear D ? :9
-
8/11/2019 04 Lathe Operations
23/31
E%ercise *). 'alculate change gears to cut R.H. single start threads of 4.(+0
pitch on a lathe ha!ing a lead screw of 2 mm lead.
Soln.:
Compound 1ear Train with no idler%
1ear > ? 37:& 1ear B ? @8&
and
1ear C ? 98& 1ear D ? 388
-
8/11/2019 04 Lathe Operations
24/31
Setting of Tools for Threading
!ig )etting threading toolfor internal threading
!ig )etting threading tool for
external threading
Cutting tool should $e set exactly atthe height of centers and normal to the
work piece axis
If it is incorrectly set, the thread angle
will not $e correct and the flanks formed
will not $e proper
This setting is essential $oth for external
and internal threads
> center ga)ge is always used for
setting the threading tool correctly asshown in figures
-
8/11/2019 04 Lathe Operations
25/31
Feeding the Tool in Threading
!ig a6 )traight Thread
!ig $6 Inclined feed
!ig c6 Inclined feed using a form tool
0arge amount of material is removed in the form of
chips and that leads to the (amming of the tool and
the flanks of the threads will $e rough
0imit only to the finishing on coarse threads
/owever, it can safely $e used for threads having
$elow 7 mm pitch
In this method 5!ig $6 tool is fed at an angle 5usually
half of the thread angle6 to the axis of the work
The tool is set, as usual, s;uare with the work axis
and the re;uired inclination is o$tained $y swiveling
the compound rest
'ost of the cutting is done $y the left edge and tip ofthe tool
*hen threading is to $e done on a large scale, the
tool form shown at !ig 5c6 is preferred
This tool is normally provided with the negative rake
Conse;uently, the chips flow easily on the tool faceand the digging2in tendency of the tool is reduced
-
8/11/2019 04 Lathe Operations
26/31
%ro&iding undercut
Endercuts are necessary whencutting threads on stepped work
It allows for the overrun of the tool
after one cut is over
In the a$sence of this undercut
there is always a likelihood of the
tool running into the larger diameter
causing $ending of the (o$,
$reaking of (o$ or $reaking of
tool
The undercut should $e wide enough to give sufficient time to the
operator to disengage the half nut and withdraw the tool after
finishing the cut
Its depth should always $e slightly more than the depth of the thread
-
8/11/2019 04 Lathe Operations
27/31
Cutting S'uare and cme Thread
!ig Tool setting for s;uare threads
nceCircumferethreadofLead ..tan =
-
8/11/2019 04 Lathe Operations
28/31
Cutting (ultiple start threads
-
8/11/2019 04 Lathe Operations
29/31
Turn)uc*le
Back
-
8/11/2019 04 Lathe Operations
30/31
Lathe Operations
Figure: /arious cutting operations that can 5e performed on a lathe.
-
8/11/2019 04 Lathe Operations
31/31
Lathe Operations
Figure: /arious cutting operations that can 5e performed on alathe.
top related