Metal drilling is done cold, usually with a stand-mounted electric drill. It is also possible to drill by hand, with a chignole. The drilling tools are the drills. The drilling is used in particular for assembling parts (with bolts and nuts), but also for cutting: series of through holes and contiguous in a thick room.
- Vertical support
- Standard drilling
- Specific drilling
1. Drilling operations do not use very important equipment. The electric drill, necessary if you work the metal regularly, allows fast and good quality achievements. It is better to use a powerful drill with several speeds (or equipped with a variable speed drive), because the same speed is not suitable for all metals. A complete set of helical drills (cylindrical or tapered shanks) of different diameters, and special drilling tools: drill bits, conical cutters, straight flute drills (cuprous metals) must be used.
2. Mark the location of the hole to punch with the hammer. It is necessary to materialize the center of the circle of the hole, whatever its diameter, by drawing two intersecting axes using a tungsten carbide scribing point. The needle punch is not just a reference: it must be deep enough to guide the tip of the drill at the beginning of drilling.
3. Tighten the workpiece and insert the drill into the drill chuck. The drill supports allow the establishment of fasteners to securely hold parts. Be careful, make sure to fix the parts correctly: if they are not tight, they can be thrown and cause an accident. The helical drill is a cylindrical steel tool, filled from top to bottom with two helical grooves, allowing the evacuation of metal chips. The tip of the drill has two sharp edges that must be properly sharpened. Lower the lever on the drill bracket and check, with the machine stopped, that the needle hole and the drill tip coincide exactly.
4. Drill by gradually lowering the vertical support lever. Adjust the speed of the drill according to the diameter of the drill and metal worked: use high speeds for small diameter drills and small speeds for large diameters. The harder the metal, the lower the speed of the drill. If you drill a through hole, weigh less on the lever at the end of the hole. To pierce metal plates, place a wooden martyr block below.
5. For a thick piece, the method of preparation remains the same: needle punch with the hammer. Place the piece on the support tray and secure it.
6. For metal pieces over 10 mm thick, drill a pilot hole by placing a drill bit 4 or 5 mm in diameter on the drill; it will then be used as a guide for the larger drill. The drilling of a pilot hole reduces the force exerted by the machine and the heating of the tools.
7. To facilitate drilling operations, a lubricant must be applied to the metal being drilled using a burette. Always stop the machine to lubricate the metal. There are commercially available lubricants specially prepared for drilling different metals: for mild steel, it is a mixture of soluble oil and sodium hydroxide, for copper, paraffin oil for aluminum, sodium hydroxide. To pierce the cast iron, you do not need to lubricate: you have to stop the machine when the tool heats up too much and let it cool down.
8. Making holes of large diameter is done with a conical bur, placed on the mandrel of the drill. Conical cutters, more or less pointed (angle at the top of 60 and 900), are mainly used to mill housing for screw heads and rivets. They are not suitable (because of their shape) to drill a hole of big diameter in a big thickness: it is better for that to use drills by practicing pilot holes to prepare the work.
9. Drilling large diameter holes in sheets and metal parts is done with drill bits (or bellsaws), which are mounted on the chuck of the drill as an ordinary drill bit. Secure the piece of metal between the jaws of the vice; determine the center of the hole by tungsten carbide tip tracing. Work at reduced speed. To obtain a good centering, draw with compass the circle to be cut. The center must be marked with a needle punch. Lubricate from the beginning of drilling to reduce the heating of the metal during work.
10. Raise the drill bit during operation to prevent overheating of the tool. The drill bit has a centering drill that drills the center of the circle at the same time that the blade cuts the circumference. It is therefore necessary to place the central drill exactly on the needle stroke.
11. Finish drilling by gently depressing the drill's lowering lever. The drill bit makes sharp and even cuts. To pierce a thicker piece, proceed slowly and allow the tool time to cool. Lubricate the metal often. Never use water to cool the metal.
12. If you do not have an electric drill, use a chignon (or drill). The drills are mounted on the chuck of this tool (as for an electric drill). After determining the location of the needle hole and attaching the workpiece, drill while holding the drill holder upright. The left hand presses on the support plate (or consciousness), and the right hand turns the crank. The gyratory movement is communicated to the mandrel by a gear pair. There are two-speed drills with crankcase (as here) or with visible gear. Drill Holders can not drill holes larger than 10 mm in diameter (with pilot hole up to 5 mm).
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