【正文】 he base and the end flank immediately below the end cutting edge。 but the possibility of charter increases. A promise must, as usual, be reached. The nose angle, number 8, is the angle between the two ponent cutting edges. If the corner is rounded off, the arc size is defined by the nose radius 9. The radius size influences finish and chatter. Sand Casting The first stage in the production of sand castings must be the design and manufacture of a suitable pattern. Casting patterns are generally made from hard word and the pattern has to be made larger than the finished casting size to allow for the shrinkage that takes place during solidification and cooling. The extent of this shrinkage varies with the type of metal or alloy to be cast. For all but the simplest shapes the pattern will be made in two or more pieces to facilitate moulding. If a hollow casting is to be made the pattern design will include extension pieces so that spaces to accept the sand core are moulded into sand. These additional spaces in the mould are termed core prints. Sand moulds for the production of small and mediumsized castings are made in a moulding box. The mould is made in two or more parts in order that the pattern may be removed. The drag half of the mould box is placed on a flat firm board and the drag half of the pattern placed in position. Facing sand is sprinkled over the pattern and then the mould box is filled with moulding sand. The sand is rammed firmly around the pattern. This process of filling and ramming may be done by hand but mould production is automated in a large foundry with the mould boxes moving along a conveyor, firstly to be filled with sand from hoppers and then to pass under mechanical hammers for ramming. When ramming of the sand is plete, excess sand is removed to leave a smooth surface flush with the edges of the moulding box. The pleted drag is now turned over and the upper, or cope, portion of the moulding box positioned over it. The cope half of the pattern is placed in position, correct alignment being ensured by means of small dowel pins. Patterns for the necessary feeder, runner and risers are also placed so as to give an even distribution of metal into the mould cavity. The risers should coincide with the highest readily escape from the mould. The sizes of risers should be such that the metal in them does not freeze too rapidly. An important function of a riser is to act as reservoir of liquid metal to feed solidification within the mould. A thin coating of dry parting sand is sprinkled into mould at this stage. This is to prevent the cope and drag sticking together when the cope half is moulded. The cope is now filled with moulding sand and this is rammed firmly into shape in the same manner as in the making of the drag. After the ramming of sand in the cope is pleted the two halves of the moulding box are carefully separated. At this stage venting of the moulding box are carefully separated. At this stage venting of the mould can be done, if necessary, to increase the permeability of the mould. After venting the patterns are carefully removed from both cope and drag, and a gate or gates are carefully cut to connect the runner channel with the main cavity. Gates should be sited to allow or entry into mould with a minimum of turbulence. Any loose sand is gently blown away and if a core is to be used it the cope upon the drag and it is then ready for use. Liquid metal is poured smoothly into the mould via the feeder. Pouring ceases when liquid metal appears at the top of the risers and the feeder channel is also full. When the metal that has been poured into a sand mould has fully solidified the mould is broken and casting is removed. The casting still has the runner and risers attached to it and there will be sand adhering to portions of the surface. Runners and risers are cut off and returned to the melting furnace. Sand cores are broken and adherent sand is cleaned from the surface by vibration or by sand blasting with dry sand. Any fins or metal flash formed at mould parting lines are removed by grinding and the castings are then ready for inspection. The main Elements of Horizontal Milling Machines Column and base The column and base form the foundation of the plete machine. Both are made from cast iron, designed with thick sections to ensure plete rigidity and freedom form vibration. The base, upon which the column is mounted, is also the cuttingfluid reservoir and contains the pump to circulate the fluid to cutting area. The column contains the spindle, accurately located in precision bearings. The spindle id driven through a gearbox from a veebelt drive from the electric motor housed at the base of column. The gearbox enables a range of spindle speeds to be selected. In the model shown, twelve spindle speeds from 32 to 1400rev/min are available. The front of column carries the guideways upon which the knee is located and guided in a vertical direction. Knee The knee, mounted on the column guideways, provides the vertical movement of the table. Power feed is available, through a gearbox mounted on the side, from a separate builtin motor, providing a range of twelve feed rates from 6 to 250mm/min. Drive is through a leadscrew, whose bottom end is fixed to machine base. Provision is made to raise and lower the knee by hand through a leadscrew and nut operates by a handwheel at the front. The knee has guideways on its top surface giving fullwidth support to the saddle and guiding it in a transverse direction. lock is provided to clamp the knee in any vertical position on the column. Saddle The saddle, mounted on the knee guideways, providers the transverse movement of the table. Power feed is provided through the gearbox on the knee. A range of twelve feeds is available, from 12 to 500mm/min. Alternative hand