Make sure that your steel is straight. Bent steel is nearly impossible to use effectively and a poorly placed blow could glance and cause an injury. Keep the steel sharp. Sharp steel helps you work safely and efficiently.
Use a double cut file or grinder to redress steel that is not badly worn. Maintain existing edge bevels as much as possible. In the field file the heads smooth and cutting edges sharp. Use a completed hole as a holder. Insert the steel upside down and brace it with your knee or foot. Your partner may also hold the steel while you file. Always wear gloves when sharpening or holding.
When using a grinder, remember to avoid excessive heating of the steel that could draw temper and soften the bit. Be aware that forged tools are harder on the outside than they are at their core. Careless or excessive grinding or filing can expose the core and cause premature dulling.
Using a hole as a holder.
One worker may hold the steel while the other files.
Reconditioning and Tempering
The facilities and expertise of a blacksmith will almost certainly be required to completely recondition dull drilling steel. Here is an historical account describing how a blacksmith worked:
"Drills are sharpened, first by forging to the right shape and to give a sharp edge; this edge, however, by many smiths is not hammered sufficiently sharp, and they use either a file or a grindstone to give the required edge. The point is then heated to a glowing red and dipped in cold water for a few seconds to harden the steel; the edge is then rubbed on sand to clean it. The smith examines for the colour, and dips at a pale straw colour to make it hard, or at a dark blue, which makes it a little tougher. If, after the first cooling, there is not sufficient heat in the drill for these colours to show on the edge, it must be reheated in the fire. When the drill is dipped for tempering, it may remain in the water till cold. The exact colour at which steel has to be dipped varies with the quality of the steel, and also, no doubt, with the nature of the work, but a little practice will soon show." (Lupton, 1906).
Special variations in the temper and length of steel were sometimes required to drill particularly hard rock.
Modern hand drilling steel has similar forging requirements. In the reconditioning process it is important for the blacksmith to be able to control the hardness of steel by tempering. In general, the harder the steel, that is, the more cohesive the particles of metal, the more resistant the tool will be to wear. If the steel is made too hard, however, it may become brittle and break during use.
Standards for the hardness of tempered steel have been established that guide smiths to the correct hardness for a tool based on its usual range of applications. Hardness is measured by pressing on tempered surfaces with specific shapes under a known pressure. The amount of pressure that the tempered metal is able to withstand before an indentation is made becomes a measure of its hardness. The best known measures of hardness of tempered steel for tools are Rockwell and Brinell hardness. Rockwell hardness tests measure the indentation of a diamond cone (Rc), or a steel ball of a specified diameter (Rb), on a tempered surface. Brinell hardness tests measure only with a ball (HB) (see Hardness Testing Conversion Table).
The steel on the tool's surface is slightly harder than the steel in the middle. This is because during the quench the particles on the surface are more radically affected; they are more cohesive than those in the middle or slightly beneath the surface. The key to tempering is to retain the desired toughness at the center of the tool. The softer core assures a strong tool, while the hard exterior provides the cutting edge or protective shield.
Here is a description of a modern tool reconditioning process:
Heat the point to a yellow color (1800 to 1900°F/982 to 1038°C), for the length necessary to forge. Be careful not to heat too far back on the steel; this is the most common cause of premature breaking after reconditioning. Do not attempt to forge below a cherry red color, (1450°F/790°C) (see Incandescent Colors and Temperatures chart).
Rework tools only to their original design.
After forging allow the tool to cool to room temperature.
- Reheat the point to a cherry red color 1 1/2 to 2 inches back from the cutting edge, making sure to overlap the forging depth
- Quench in water, or in a brine or oil solution. Maintain the quench at a temperature of 75 to 100°F/24 to 38°C, to achieve Rockwell hardness (Rc) 60 to 65, Brinell hardness (HB) 600 to 652
Withdraw the tool from the quench with sufficient heat remaining in it to draw the temper. A shade of brown or dark yellow is best.
Rub the point clean with emery.
When a light straw color appears, (430°F/222°C), complete the quench.
If drawing facilities are available, reheat to 425°F/ 218°C, and hold for 1 hour to achieve Rc 56 to 60, H B 555 to 600.
Temperatures will vary among types of tool steel.
This operation should be undertaken only by or under the close supervision of an experienced blacksmith who knows the specific requirements of the steel he uses.
Wear adequate protective clothing, including eye protection and gloves, at all times.
If your drilling steel includes short 'starters' and longer 'seconds', the smith should make the cutting bits diminish slightly in width as the rods increase in length. This is necessary to prevent jamming when a new length of steel is started in the hole. A drilled hole gradually decreases in diameter as the tool wears. The bore-hole is not a true cylinder, but the frustum of an elongated cone. If the head of the steel becomes mushroomed from extended use, it should be reshaped by the blacksmith during reconditioning.
The bore-hole is not a true cylinder,
but the frustum of an elongated cone.
Defective Steel and Prolonged Safe Use
Although drilling steel is designed to perform in demanding applications, few products are subjected to more stress in service. Hand-hammered percussion tools for drilling and wedging must endure the same punishment as the rock being worked, so some failures may be expected.
Defective steel is likely to fail early on due to the severe stresses from the blows of the hammer, although some break after considerable service without having been defective. To insure long life and safe use of drilling steel, avoid these common causes of premature failure:
Using steel for an unintended purpose. Prying with the steel, for example, will bend it and render it unsafe and ineffective.
Allowing steel to overheat in service. This will draw temper and cause cutting edges to soften and dull.
Failing to keep the steel sharp. This causes extra stress on the rod.
Redressing steel inadequately or improperly. Tools improperly forged and rehardened or excessively filed will dull quickly, mushroom prematurely, and break before giving a full measure of service.
Using hammers with cracked handles, loose heads, or chipped faces is a safety hazard as well as a reflection of poor maintenance. Examine handles to insure that they are tight on heads and free of cracks. If handles have been poorly maintained or neglected, take time to repair or replace them before beginning a drilling job.
Striking faces should be smooth and evenly worn. Drilling hammers have hard tempered faces designed to strike softer drilling steel heads. The head of the steel mushrooms and the hammer face remains smooth. If a hammer face becomes pitted or chipped, however, carefully grind it smooth. Work slowly to avoid damaging the shallow temper of the face. Discard badly worn hammers. Some hammers have faces tempered soft to mushroom with use. These allow workers to safely hammer hard metals without the hammer face chipping. Mushroomed hammer heads can also be reconditioned by a blacksmith.
Wedge and feather sets should generally be treated like drilling steel. Avoid using wedges alone to break rock. Wedge tips are not tempered hard enough to start holes. Hammer wedges primarily on the heads, and avoid striking feathers as much as possible. Remember also that wedge and feathers break rock with friction and stress, so overheating can occur.
When sharpening picks grind the tips to a point 1/8-inch square. This will make a sharp, effective point that is strong enough to resist breaking. Before sharpening secure the head in a vise or special jig. Sharpen with an electric grinder or a 10-inch mill bastard file. Badly damaged picks can also be reforged by a blacksmith.
An oval-tapered eye and handle allow pick heads to tighten when swung, while remaining removable for sharpening, transporting, and handle replacement. A small screw in the handle just below the head will further fasten heads to handles.
Pick secured for sharpening without a vise.