A hack saw is a saw used for cutting various types of metals. It consists of a thin serrated steel blade mounted on an adjustable bow frame fitted with a pistol grip handle or straight hardwood grip handle at one end. A pistol grip handle is preferable, since it is much less prone to twisting in the hand during use, thus giving a cleaner cut. Frames are available to accommodate 8, 10 and 12 inch long blades.
Power hacksaws are also available; these are a type of hacksaw powered either by its own electric motor (also called an electric hacksaw) or connected to a stationary engine. Most power hacksaws are large stationary machines, although some portable models do exist. Stationary models typically feature a mechanism for lifting up the saw blade on the return stroke; some include a coolant pump to prevent the saw blade from overheating.
Stationary electric hacksaws are fairly uncommon, although are still manufactured, but saws powered by a stationary engines are obsolete. Power hacksaws are used because they give a cleaner cut than an angle grinder or other types of saw, and are faster than a manual handsaw. They are mostly seen in industrial settings and large metal working shops.
Hack Saw Blades
To suit the material being cut, blades are available with different sizes of teeth. Typical sizes range from 14, 18, 24 and 32 teeth per inch. Fine teeth are used for sawing through thin sheet materials and harder materials, while coarser teeth are used for softer metals such as aluminum, which clog up finer teeth. Coarse teeth are set in the saw in the “raker” pattern; alternating left to right in order to clear away metal chips efficiently.
The best blades for all around work are of flexible steel with hardened teeth. A fully hardened blade, although capable of producing more precise cuts, is more brittle and prone to breakage. If you are using a fully hardened hacksaw blade, practice on a piece of scrap material before cutting your real work piece.
How to Use a Hacksaw
Begin by firmly securing your work in a vise or clamp. Using your thumb as a guide, make short backward strokes to set up the cut. Proceed with the cut, making full length strokes, using both hands, one gripping the handle, the other holding the front of the frame. Cut back and forth with a steady rhythm, applying pressure on the forward stroke only.
For cutting thin sheet metal, hold the hacksaw at an angle to piece so as to keep more teeth in contact with the metal. For cutting thicker sections, saw to the depth of the blade, then rotate the work to the next side; you want to saw on all sides, working your way to the middle of the piece. Add some light oil as a lubricant. Finally, cut away the metal remaining in the center, while using the previous cuts on all sides as a guide.
For cutting sheet metal, a trick to help make a good cut is to sandwich your work between two pieces of plywood. Wandering off the cut line by the saw is typically caused by twisting the saw frame; check your grip and make sure both hands are in the same plane.
The blade of a hack saw is held under tension by wing nuts located on each end of the frame. In order to remove a worn or broken hacksaw blade, you need to loosen the nut until the blade can slip free of the frame. Hook the holes in the ends of the new blade onto the locating pins, with the blade teeth facing away from the handle. Now tighten the nuts.
Getting the proper tension on the blade is a matter of trial and error. If you tighten so that too much tension is on the blade, it will arch up to the top of the frame and not flex enough. If you leave the blade too loose, however, it will bend sideways when you are trying to make a cut and may even snap. You want to have the blade somewhere in between the two extremes.
Another adjustment you can make to the blade when replacing it is to orient it at an angle to the frame. The locating pins are on a spigot piece which has a square shoulder fitting into the frame. The spigot can therefore be rotated into one of four positions 90 degrees apart so that the blade teeth can go sideways or inverted. This is useful for making cuts longer than the frame would otherwise permit or where there is limited access.
See Also: How to Sharpen a Hand Saw
Junior Hack Saws
For even more confined spaces, the 6 inch long Junior hack saw is useful, although it is only for making fine cuts. One type of this hacksaw has a one piece frame and handle made from a single bent metal rod. The 32 teeth per inch blade is held in tension naturally by the spring of the frame and is fixed in place with slots on the handle and pins on the blade.
Another model of the junior hacksaw is more like its big brother, with a pistol grip, flat steel frame and spigot type tensioning mechanism. For even more confined spaces, there is the Mini Hack Saw, comprised of a one piece plastic frame and handle holding a short blade. The blade conveniently slides into the handle for storage, held in place by a screw clamp at one end.