Metalwork - Bench Tools - Hacksaws
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.
(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.
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.
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.
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.
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.
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 damage to the blade or hacksaw, or more importantly to your hands.