| Many industrial concerns have workshops of their | | | | multiplepoint. The lathe and shaping machine use |
| own. For therepair of worn shafts, the lathe | | | | single point cutting toolwhile the milling and drilling |
| machine is excellent. Keywayslots can be | | | | machines use multiple-point-cuttingtools. |
| machined by using a milling machine, while ashaping | | | | Metal is cut either by moving the work piece like |
| machine can do machining of large flat areas. | | | | in the lathe orby moving the tool like in the |
| Adrilling machine does drilling of holes. | | | | shaping machine, drilling ormilling machine. Clearance |
| A skilled Maintenance Engineer should know how | | | | angles must be provided to prevent thetool |
| to use all thesemachines in order to make his own | | | | surface below the cutting edge from rubbing |
| repairs in a safe manner. Veryoften he has to | | | | against the workpiece. Rake angles are often |
| supervise machinists. The information belowshould | | | | provided on cutting tools to cause awedging |
| be useful for that purpose. | | | | action in the formation of chips and to reduce |
| Lathe Machine | | | | friction andheat. |
| The lathe machine uses a single-point-cutting tool | | | | Tool Materials |
| for a varietyof turning, facing, and drilling jobs. | | | | In order to remove chips from a work piece, a |
| Excess metal is removedby rotating the work | | | | cutting tool must beharder than the work piece |
| piece over the fixed cutting tool to formstraight | | | | and must maintain a cutting edge at |
| or tapered cylindrical shapes, grooves, shoulders | | | | thetemperature produced by the friction of the |
| andscrew threads. It can also be used for facing | | | | cutting action. |
| flat surfaces onthe ends of cylindrical parts. | | | | Carbon Steel |
| The work piece is clamped onto a horizontal | | | | Carbon steel tools even though comparatively |
| rotating shaft by a | | | | inexpensive tend tolose cutting ability at |
| 3-jaw or 4-jaw chuck. The latter chuck can be | | | | temperatures around 400 degree F (205degree |
| used to cutoff-centered cylinders. The rotating | | | | C). |
| horizontal spindle to whichthe chuck is attached is | | | | High-Speed Steel |
| usually driven at speeds that can bevaried. | | | | High-speed steel, containing 18 percent tungsten, |
| The cutting tool is fixed onto a tool rest and | | | | 4 percent chromium, |
| manipulated byhand. It can also be power driven | | | | 1 percent vanadium, and only 0.5 to 0.8 percent |
| on straight paths parallel orperpendicular to the | | | | carbon, permits theoperation of tools twice or |
| work axis. This is useful for screw cutting. | | | | three times the speeds allowable withcarbon steel |
| Internal turning known as boring results in the | | | | Cast Alloys |
| enlargement ofan already existing hole. The holes | | | | Cast-alloy cutting-tool materials containing cobalt, |
| are more accurate inroundness, concentricity, and | | | | chromium, andtungsten are effective in cutting |
| parallelism than drilled holes. Ahole is bored with a | | | | cast iron and retaining theircutting ability even |
| single-point-cutting tool that feeds alongthe inside | | | | when red hot. |
| of the work piece. | | | | Cemented Tungsten Carbide |
| Shaping Machine | | | | The hardness of Tungsten Carbide approaches |
| The shaping machine is used to machine flat | | | | that of a diamond. |
| surfaces, grooves,shoulders, T-slots, and angular | | | | Tungsten carbide tools can be operated at cutting |
| surfaces with single-point tools. | | | | speeds many timeshigher than those used with |
| The cutting tool on the shaper oscillates, cutting | | | | high-speed steel. |
| on the forwardstroke, with the work piece | | | | Oxides |
| feeding automatically toward the toolduring each | | | | Ceramic, or oxide, tool tips consist primarily of |
| return stroke. | | | | fine aluminum oxidegrains, which are bonded |
| Drilling Machine | | | | together. These are very hard. |
| The drilling machine is used to cut holes in metal | | | | Cutting fluids |
| with a twistdrill. By changing the cutting tool, they | | | | An overheated tool can become blunt and soft |
| can be used to doreaming, boring, counter boring, | | | | very fast. Thereforevery often, cooling fluids |
| countersinking, and threading. | | | | cools the cutting points of the tool. Thisserves to |
| Milling Machine | | | | lubricate and cool. |
| The milling machine uses a rotating cutting tool to | | | | Water is an excellent cooling medium, but it |
| cut flatsurfaces, grooves, and shoulders, inclined | | | | corrodes ferrousmaterials. Sulfurized mineral oil is |
| surfaces, dovetails,and T-slots. Cutters of many | | | | one of the most popular coolantsas it can both |
| shapes are changed to cut differentgrooves. | | | | cool as well as lubricate. The sulfur prevents |
| Cutting Tools | | | | chipsfrom the work from melting on to the tip of |
| Metal-cutting tools are classified as single point or | | | | the tool. |