Metalwork - Bench Tools - Hacksaws
The Hacksaw
The Hacksaw is used for cutting materials, and for cuttign away waste parts of the work. Most Hacksaws are made from Low Tungsten Steel or Carbon Steel, however the more expensive blades are made from High Speed Steel.
Frame : There are two types of Hacksaw Frame,
a fixed and an adjustable. The fixed frame can
only take one length of Blade, but is more rigid
that the adjustable type, which can take Blades
of different lengths.
Blade : There are also two main types of Blades,
but in the case of both, the teeth on the Blade
are facing away from the Handle towards the
front of the hacksaw.
The first type of Blade is the All Hard
Blade which has been hardened throughout. As
a result there is more efficient cutting but the
blade tends to break more easily.
The second type of Blade is the Flexible
Blade which has headened teeth but the
remainder of the body remains soft. The Blade,
as a result, is more flexible and breaks less
easily. It is an ideal blade for the school
workshop as it will take rougher treatment.
When fitting a new blade to a hacksaw, point
the teeth forward, (away from the handle).
Tighten the wing nut to remove the slack and
then as a general rule tighten three
turns. It is important to have the correct
tension on the blade, if it is too loose then
the blade will buckel and not cut straight, and
if it is too tight damage to the blade ends or
the frame may result.
Handle :There are three types of Hacksaw Handle used :
(a) File
Handle or Straight Handle
(b) Pistol Grip Handle
(c) Woodsaw Handle
The most commonly used handles are the File Handle and the Pistol Grip Handle.
The Junior Hacksaw is used with Blades of
150mm in length only. The tension on the blade is
formed by the frame. It is used for light work where
the normal Hacksaw would be too clumsy.
Another type of Junior Hacksaw, which is
not shown, is tightened and loosened by means of a
knurled spindle at the handle end.
Teeth & Blades
A Blade is classified by the number of teeth per 25mm of the Blades length. To make the most of a Blade and do less damage it is good to know what number of teeth should be used in each circumstance.
| Teeth per 25mm | Use |
| 14 | Soft thick materials. Aluminium, Copper, Mild Steel |
| 18 | General use. Soft materials in thin sections. Hard materials in thick sections. |
| 24 | Thin section hard materials. |
| 32 | Very thin materials such as thin tubing and sheet metal. |
It is also very important, especially when working with thin sections, that you are using a Blade with the correct number of teeth. Below you can see diagrams of bar and tube being cut. You should have at least three teeth of the blade to the thickness of the material otherwise the blade will keep catching the material being cut.
Correct
Incorrect
You will notice when you are
working with hacksaws and blades that the
teeth do not follow on directly behind
eachother. The teeth are slightly offset
from eachother. This is called the Set of the teeth. You can see, in the
diagram to the right, on top the set of coarse
teeth and on the bottom the set of fine
teeth.If you examine the blade of a normal hacksaw you will see the teeth are set as in the top diagram, and if you look at the set of a Junior Hacksaw blade you will see they are like in the bottom diagram.
The purpose of the Set is so that the blade will cut a slot wider than itself so that the body of the blade will not jam or rub against the edges in the slot. Also the Set breaks the chips cut by the teeth and helps the teeth to clear themselves.
Hacksawing Method
You should hold the work in the vice so that as many teeth as possible are in contact with the surface. This generally means that the widest edge of the work is facing up in the vice. You should also orientate the work so that you are cuttign vertically toward the floor.
 |
 |
Correct |
Incorrect |
Sixty strokes per minute is the correct rate to cut with the type of blades you will generally be using in the metalwork room. You should use the entire length of the blade and lean only slightly on the hacksaw. Leaning heavily on the hacksaw or cutting at a faster rate does not gain you anything. When you come close to the end of the cut you should decrease the rate at which you are cutting and also decrease the pressure. If you don't do this then you risk serious dame to the blade or hacksaw, or more importantly to your hands.