This document discusses power hacksaws, which are used to cut large pieces of metal like steel that would be difficult to cut by hand. It describes the main parts of a power hacksaw, including the reciprocating frame that moves the saw blade back and forth to cut the metal. The document outlines different types of power hacksaw drives and feed mechanisms that control the downward pressure of the blade. It provides guidance on operating a power hacksaw safely, including using coolant fluid to lubricate the blade and prevent overheating.

1. Mechanical Engineering

2. Power Hacksaw

3. Objectives
State safety precautions associated with
power saw
Identify the main parts of the saw
Set up work and select speeds and feeds
Perform cutting operations (square cutting,
angular cutting)

4. Power Saws
Power saw are used to cut stock to the desired
length. It is more accurate than hand saws.

5. Power Hacksaw
Power hacksaws are used to cut large sizes
(sections) of metals such as steel. Cutting
diameters of more than 10/15mm is very hard
work with a normal hand held hacksaw. Therefore
power hacksaws have been developed to carry out
the difficult and time consuming work. The power
hacksaws main feature is its reciprocating frame.
The heavy ‘arm’ moves backwards and forwards,
cutting on the backwards stroke with the help of a
downward force.

6. Parts of the Power Hacksaw
Base
A mechanism causing the saw frame to
reciprocate
Clamping Vice
Frame
Table
Feed knob
Coolant pump

7. Types of Power Hacksaws
Direct Mechanical drive
Hydraulic drive

8. Direct Mechanical Drive

9. Hydraulic Drive

10. Feed Mechanism
The feed mechanism regulates the amount
of downward pressure the blade applies on
the material during the forward stroke.

11. Types of Feed Pressure
Mechanical Feed- light
feed pressure on soft
materials and work with
small cross-section.
Hydraulic Feed- constant
pressure but designed that
when hard spots
encountered, the feed stop
or decrease the pressure
until the hard spot has
been cut through
Gravity Feed-
which provides for
the weights on the
saw frame. These
weights can be
shifted to increase
or decrease the
pressure

12. Operating the Power Hacksaw
The metal to be cut is held in a machine vice
which is an integral part of the base. Turning
the handle tightens or loosens the vice. The
vice is very powerful and locks the metal in
position.

13. Operating the Saw
When cutting is taking place, the metal and especially the
blade heats up quickly. Coolant should be fed onto the
blade, cooling it down and lubricating it as it cuts through
the metal.
Without the use of coolant the blade will over heat and
break/snap. This can be dangerous as the blade can break
with powerful force, shattering.

14. When the metal is placed and fixed in the vice,
the blade is lowered onto its top surface.
The diagram below shows the ‘arm’ being
lowered with the ‘adjusting handle’.

15. Driving Mechanism
Circular motion is transformed into linear
motion. The crank which is the rotating disc,
the slider which slides inside the tube and
the connecting rod which joints the parts
together.

16. Driving Mechanism
If the belt is placed on the smaller pulley wheel the speed of
cut will be fast. Changing the belt so that it runs round the
larger pulley wheel will reduce the speed

17. Types Of Blade
When selecting the
blade at least three
teeth must be in
contact with the
work at all times.
Flexible- used for
cutting odd shapes
and is shatter proff.
All hard- straight
and accurate cutting
but shatter when
breaks.

18. Blade Pitch
The correct pitch of teeth is determined by:
The size of the section,
The material to be cut

19. Type of Pitch
Coarse- soft steel, cast iron and bronze
Regular- anneal high carbon steel and high
speed steel
Medium- for solid brass stock, iron pipe,
and heavy tubing
Fine- thin tubing and sheet metals

20. Safety
Never attempt to mount, measure or remove
work unless machine is turned off
Guard long materials at both ends
Use cutting fluid whenever possible
Hold thin materials flat in the vice to
prevent breaking of blades