Hacksaw

Hacksaw

Purpose

Hacksaw is a hand tool, which is use for cutting of material or parting off.

Parts of a Hack Saw

Types of Frame

There are mainly two types of frames

1. FIXED TYPE: - It can hold one type blade mostly 12inch blade.

2 ADJUSTABLE TYPE: - It has provision to hold 10inch blades also apart from 12inch blade.

Parts of a Blade

The blade consists of the following parts.

1. Nominal length

2. Pin holes

3. Teeth

4. Back Edge

5. Side

6. Width

Types of Hacksaw Blades

1. High carbon steel blades:-used for soft materials and at low speed on steel productivity is less but their cost is Low.

 2. HSS Blades: Used for harder and tougher materials can be used at higher speeds on M.S and soft materials. Productivity is high but costly          roductivity is less but they are cheap

Tooth Angles on Blade

 α. Clearance Angle

β.Wedge Angle γ. Rake Angle

Pitch of Hacksaw Blade

The distance between two adjustment teeth is called the pitch of the blade. It is denoted in mm to as NO.OF.TEETH per inch cm. The pitch indicates the coarseness to fineness of the blade i.e., the grade of the blade.

Different Grades of Blades.

       According to the pitch, there are coarse, medium and; fine blades. Coarse blades are selected for bigger work pieces and soft materials.Medium grade blades are selected for general type of work. Fine blades are selected for thin work pieces and hard materials. Usually, fine blades are made with 0.8 mm pitch, medium blades with 1.0 mm pitch and coarse blades with 1.4 to 1.8 mm pitch.

Setting of Hacksaw Teeth

The teeth of the hacksaw blade are arranged in such a way that the slot cut by the blade is slightly bigger than the thickness of the blade. The difference between the thickness of the blade and the width of the cut is called ‘Kerfs’ and the arrangement of teeth to get the ‘Kerfs’ is called ‘set’. There are 3 types of hacksaw blade teeth, commonly used.

1. RAKER SET (STAGGERED TEETH):

     In this set one tooth is bent on one side while the next is kept straight and the third is bent on the other side. This set is adopted for general purpose blades.

2. ALTERNATE SET:

     In this set one tooth is bent on one side with the other one is bent on the opposite side. This is generally used on coarse teeth blade.

3. WAVY SET (UNDULATED TEETH)

     In this type of set two or more teeth are bent alternately to left and right direction at a certain angle resembling a wave snake movement. Fine and very fine blades are made with this type of set.

Cutting Speed in Hacksawing

Cutting speed in hack sawing is the no. of cutting stokes made in one minute, expressed as stroked/ min. It depends on the material of the blade and the material of the work piece.  The recommended strokes/ min for different materials are given below 

S.NO	BLADE MATERIAL ______________ WORK MATERIAL	HSS	LOW ALLOY	CARBON STEEL
1	TOOL STEEL	50	40	30
2	CAST IRON	50	40	30
3	MILD STEEL	70	60	40
4	BRASS STEEL	80	70	60
5	COPPER	90	80	70
6	ALUMINIUM	100	90	80

Rules for Hacksawing

1. Check whether the blade is properly tightened and the teeth are pointing in the forward direction. A loosely held blade will get twisted and will break.

2. Hold the handle with the right hand and grip the other end of the frame with left hand.

3. Hacksawing is a pulling action do not push the saw but pull it with left hand should only guide the saw.

5. Use full length of the blade.

6. Do not use a new blade to finish a work started by an old blade. As the kerfs made by an old blade is smaller than the new blade, the new blade will get stuck up in the slot and the teeth will break

7. Forward stroke slow and with pressure and back ward stroke fast and without pressure.

8. Ensure that at least 3 teeth cut the work at the same time.