1. OUTLINES MODULE 1 Safety precautions Types of Sawing m/c
Blade terminology
Tooth forms
Set patterns
Blade length calculations
Cutting fluids

2. SAFETY PRECAUTIONS WHEN WORKING WITH POWER SAWS
Mount or remove work only when the saw is stopped.
Clamp the w/p securely.
Use only blades that are in good condition and which are the correct kind for the material being cut.

3. Operate the machine at a cutting speed and feed rate that does not strain the machine or the blade.
Keep hands away from the saw blade when it is running.
Stand out of line with the blade when starting an abrasive cutoff saw.
Do not bend over in front of a power hacksaw frame when the m/c is running.

4. SAWING MACHINE TYPES 1. Reciprocating : Power hacksaws
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SAWING MACHINE TYPES
1. Reciprocating : Power hacksaws
2. Circular saw: Cold saw & abrasive
3. Band saw: Horizontal, vertical cutoff

5. Fig. Reciprocating power hacksaw
Reciprocating Sawing Machines: Hacksaws :
Used primarily for cutting to length metal of various sizes & shapes.
These sawing m/c vary in design from light-duty to heavy-duty m/c.
Actual cutting takes place in only one direction and the saw blade is lifted slightly on the return stroke.
Fig. Reciprocating power hacksaw

6. Fig. Power hacksaw

7. Abrasive discs are also used for cutting off stock.
An abrasive disc is a thin, flexible grinding wheel.
The disc is mounted on a machine that can be adapted for either wet or dry cutting.

8. The following factors affect the selection of an abrasive saw:
1. Material to be cut
2. Size of material
3. Cut to be made dry or with cutting fluid
4. Degree of finish desired and acceptable burr.

9. Abrasive materials:
Aluminum oxide: Used for cutting most metals including steel
Silicon carbide: Used for cutting nonmetallic material such as stone
Diamond: Used for cutting extremely hard materials such as glass

10. Horizontal Band saws
Are available in a wide variety of types and sizes.
It has a flexible, "endless" blade which cuts continuously in one direction. The thin blade travels over the rims of two pulley.
The saw frame, hinged at the motor end, has two pulley wheels over which the continuous blade passes.
The step pulleys are used to vary the speed of the continuous blade.
The roller guide brackets provide rigidity for a section of the blade and prevent it from wandering and twisting.

11. The blade tension handle is used to adjust the tension on the saw blade.
The vise mounted on the table can be adjusted to hold various sizes of w/p.
BLADE TENSION
Fig. The main parts of horizontal Bandsaw

12. BAND SAW BLADE MATERIALS
(1) Carbon-alloy,
(2) High-speed alloy steel,
(3) Tungsten Carbide-tipped blades

13. Advantages of Band machines
A minimum amount of material is wasted
Contouring ability, that is, the ability to cut intricate (complex) curved shapes
There is no limit to the length , angle or direction of the cut
W/P larger than the m/c can be cut.

14. Saw Blades - Terminology
Blade Kerf - width of the cut produced by the blade.
Blade Width - distance from the tip of the tooth to the back of the blade.
Blade Gage - thickness behind the set of the blade.
Blade Pitch - is the number of teeth per inch.

15. Tooth Forms Tooth Form - The shape of the saw tooth.
Three types of tooth forms:
(a) Precision or Regular Tooth or Standard- This is the most generally used . It is used when a fine finish and an accurate cut are required.
(b) Buttress or Skip Tooth - This tooth form is similar to the precision tooth; however, the teeth are spaced farther apart Used on thick work sections and on deep cuts in soft material.
(c) Claw or Hook Tooth –
It is faster cutting and longer lasting than the buttress tooth, but will not produce smooth finish.
Tooth Form - The shape of the saw tooth.

17. There are three common set patterns (1) Wavy :
Alternate arrangement of several teeth to right and left.
Used to cut tubes & light sheet metal.
(2) Straight : One tooth left & the other right.
Used for brass, copper & plastic
(3) Raker :
Three teeth in sequence left, right, & straight.
Used for steel & cast iron

18. Common set patterns

19. Tooth Angles

20. Blade Length Calculation
2* CD+3.14*D
CD= CENTER DISTANCE
D= DIA OF PULLEY

21. Example:
Calculate the length of a saw blade for a band saw which has:
Two 24 in. diameter pulleys and a center-to-center distance of 48 in.
(b) Two 600 mm diameter pulleys and a center-to-center distance of 1200 mm.
Solution:
Blade length = 2(CD) *D = 2(48) + (3.14* 24 )= in
Blade length = 2(CD) *D = 2(1200) + (3.14*600)= 4284 mm

22. Using Cutting Fluids
Cutting fluids will dissipate much of the heat & greatly increases the life of the blade.
Produce a smoother finish
Function as a coolant & lubricate the blade
Transport chips out of the cut.
Common fluids are oils, oils dissolved in water or soluble oils & synthetic chemical cutting fluids.

23. Problems in Band Welding
Misaligned pitch or tooth spacing incorrect,
Blade misalignment,
Insufficient welding heat, or too much welding heat.
Tooth spacing incorrect
To much welding heat
To little welding heat
Blade misalignment

24. Kerf of the band blade is narrow as compared with that of the reciprocating hacksaw or abrasive saw.
Minimum amounts of material are wasted in sawing.

25. Selection of blade:
Material to be cut
Thickness
Cross-sectional shape of the w/p