Saw blades CHARACTERISTICS Classification of sawing operation & machines

1. MANUFACTURING
PROCESS-1
PREPARED BY:
PARTH SHAH
DHARAMJEET JADEJA
SANJAY PARMAR
PURAV VYAS

2. -CONTENT
• INTRODUCTION TO METAL SAWING
• CHARACTERISTICS OF METAL CUTTING SAW
BLADES
• SAWING SPEED & FEED
• SAWING OPERATIONS & MACHINES
• FRICTION SAWING

3. INTRODUCTION
• Sawing is an important first operation in any shop subsequent machining
operation.
• Metal & other materials are often cut using sawing m/c or hand saw.
• Sawing is used because of its characteristic advantages like high speed
of cutting, low wastage of material & low power consumption.
• The process can also be easily automated leading to considerable
saving in labour cost.
• In sawing operation a large number of teeth move through the work
piece each successive tooth deepening the cut made by its
predecessor.
• Feed may be given either to the saw or the job.
• Both straight or curved profiles may be cut by controlling the direction
of feeding.

4. SAWING SPEEDS AND FEEDS
• The cutting speed for sawing is determined by essentially the same
considerations as for any other machining operation.
• For common metals speed may vary from 0.2 m/s for hard & tough
alloys to 15 m/s for soft materials.
• Feed for sawing is the rate of movement of saw into work-piece at
right angles to the speed direction and it is denoted by mm/s or
mm/stroke.
• Feed rate determines depth of cut taken by each individual tooth
and should be so adjusted that the force exerted by the work-piece
on the saw in the direction of the feed is as high as the blade would
permit without damage.
• Manual sawing is considered inferior from feed point of view
because it is not possible to ensure a definite and uniform rate of
feeding in manual sawing.

5. CHARACTERISTICS OF METAL CUTTING
SAW BLADES
Metal cutting saws are characterized by
- Material
- Tooth Form
- Tooth set
- Tooth Spacing
- Size

6. - Material
• Most good quality saw are made from high carbon or high speed
steel.
• Larger blades may have only the teeth portion made of high speed
steel while the main portion of the blade may be made of a low cost
alloy steel.
• Diamond teeth blades are used for machining ceramics and other
hard materials.

7. - Tooth Form
• The geometry of the teeth is similar to that of the single point tools.
• Two common tooth forms are the straight tooth & the undercut tooth form
shown in Fig.
• Of these the undercut profile is considered superior because the cutting teeth
are better backed up and work with a positive rake angle. But geometry is
more difficult to make on smaller teeth.
• The straight tooth form is used for light feeding rate while the undercut tooth
form is more suitable for coarse feeding.

8. -Tooth set
• Saw teeth are given an offset to the side known as set to produce cuts which
are wider than the thickness of back of the blade or disc. This is done by
bending some teeth slightly to the right or left.
• This enables the saw to move freely without friction.
• Three common types of saw tooth sets are shown in Fig.
1. A straight set has one tooth set to the right and the next to the left. Saws
with this type of set are used for cutting brass, copper & plastics.
2. In a rocker set one straight tooth is followed by two teeth set in opposite
direction. This set used for most steel and cast iron cutting.
3. A wavy set comprises of an alternate arrangement of several teeth set to
the right and several teeth set to the left. This arrangement is used for cut-
ting tubes and thin sheets of metal.

10. - Tooth spacing
• Tooth spacing or pitch has significant influence on the performance of the
saw.
• The space 𝑏𝑒𝑡 𝑛 the teeth provides room for chips removed during the cut.
• Coarse pitch is needed for larger cuts and for cutting softer materials to
accommodate the larger chips.
• Fine pitches are recommended for harder materials.
• For cuts in thin sections a fine enough pitch should be used so that at least
two and preferably three teeth always contact the work piece to prevent
stripping of the teeth.
• For band saws the pitch may be as fine as 0.75 mm.
• For hack saw 1.5 mm pitch is also considered fine.

11. - Size
• Hack saw blades are straight strips. 1 to 3 mm thick, 15 to
65 mm wide and 300 to 1000 mm long.
• Circular saw discs vary from 1 to 6 mm in thickness & 200
to 1000 mm in diameter.
• The heavier the cut larger will be blade size in general.
• Band saws run from 0.5 to 1.5 mm thick & 1.5 to 25 mm in
width.
• The narrower bands are used to cut smaller radii.

12. CLASSIFICATION OF SAWING
OPERATION & MACHINES
• RECIPROCATING OR POWER HACK SAWING
• CIRCULAR SAWING
• BAND SAWING

13. -RECIPROCATING OR POWER HACK
SAWING

15. -Power Hack Sawing
• IN THIS WORK PIECE IS CLAMPED IN VISE.
• ARRANGEMENTS ARE PROVIDED TO VARY THE LENGTH OF
STROKE PER MIN. & ALSO PROVIDE FEED CONTROL DEVICE.
• PRODUCTION HACK SAWS ARE PROVIDED WITH AUTOMATIC
FEEDING , MEASURING & CUTTING OF SERIES OF PIECES.
• DURING HACK SAWING ADEQUATE QUANTITY OF CUTTING FLUID
APPLIED FOR BETTER WORKING AND SHORTER & STRONGER
BLADES ARE USED FOR MINIMIZE BLADE BREAKAGE.
• MACHINING RATE IS LOW BUT COST IS MUCH LESS COMPARED
TO OTHERS.
• IT IS ROUGH OPERATION & GENERALLY USED FOR MAKING
SIMPLE JOBS.

16. -CIRCULAR SAWING

17. -Circular Sawing
• IN THIS SAW DISC HAVING LARGE DIAMETER IS USED FOR CUT THE
WORK PIECE.
• SAWING DISC DIA. UPTO 200 MM IS KNOWN AS METAL SLITTING
SAWS & DIA. ABOVE 200 MM IS KNOWN AS COLD METAL SAWS.
•
•WORK PIECE HELD BY SCREW CLAMP OR HYDRAULIC CLAMPING
DEVICE.
• TRIPS ARE PROVIDED FOR ADJUSTING THE LENGTH OF FEEDING.
• CIRCULAR SAW MACHINE MAY BE MANUAL , SEMI AUTOMATIC OR
FULLY AUTOMATIC.

18. •IN SEMI AUTOMATIC FEEDING OF STOCK & REMOVAL OF CUT
PIECE MANUALLY & OTHER OPERATIONS AUTOMATICALLY.
• IN FULLY AUTOMATIC FEEDING OF BAR STOCK MANUALLY &
OTHER OPERATIONS AUTOMATICALLY.
• CUTTING FLUID IS PROVIDED FOR LUBRICATION FOR TEETH
WHEN NOT USED FOR CUTTING.
• THE LENGTH TOLERANCES OF ORDER OF 0.075 MM EASILY
OBTAINED.

19. -BAND SAWING

20. -Band Sawing
• IN THIS BAND IS MADE BY WELDING FIXED THIN STRIP OVER THE
WHEELS.
• UPPER WHEEL MOVES VERTICALLY & PROVIDE TENSION TO SAW
BAND.
• BUT INSUFFICIENT TENSION LEADS TO WANDERING OF BAND & TOO
MUCH TENSION RESULTS EXCESSIVE WEAR OF WHEEL TYRES.
• WORK PIECE IS HELD ON TABLE & THE TABLE ALSO CAN BE TILTED.
• THRUST ROLLER SUPPORT IS PROVIDED AT BACK OF THE BAND TO
RESIST FEEDING THRUST.
• SAW BANDS ARE HEAT TREATED TO HAVE HARD TEETH & SOFT BACK
TO PERMIT BENDING.
• BAND SAW MACHINES ARE AVAILABLE FOR STRAIGHT CUTTING &
FOR INSIDE & OUTSIDE CONTOURING WORK.
• CONTOUR BAND SAWING IS USEFUL FOR CUTTING INSIDE & OUTSIDE
SURFACE OF SMALL TOOLS , FIXTURES & GUAGES.

21. • BAND SAWING IS CONTINUOUS & FASTER THAN HACK SAWING
BUT FOR SIMPLE OPERATION IT BECOMES COSTLIER.
• BUT IN THIN WEAK WORK PIECE BAND SAWS ARE FAST &
ACCURATE LIKE CIRCULAR SAWS.
• BAND SAWS ARE GENERALLY THINNER SO THAT LESS MATERIAL
IS LOST AS CHIPS.

23. -Friction Sawing
• Burning process by which saw band (with or without) saw teeth, is
run at high speeds to burn or melt its way through metal
• 10,000 to 25,000 sf/min
• Cannot be used on solid metal
• Amount of heat generated
• Excellent for cutting structural and honeycombed parts of machine
or stainless steel

24. -Friction sawing has the following advantages
compared to conventional metal sawing :
1. Frictional sawing is several times faster then conventional
metal sawing. A 150 mm diameter steel pipe can be cut in
less than 60 seconds.
2. Hardened steel and other steel which cannot be cut by
conventional methods can be easily cut by friction sawing
without annealing.
3. The forces on the work piece are low and hence work piece
can be easily hand fed.

25. -The disadvantages of friction sawing
include:
1. Friction sawing procedure a less accurate surface and leaves a
heavier burr.
2. The process is limited to thin ferrous metals and some
thermoplastic plastics