Friends, the topic that is going on today is about the classifications of milling machines. In which we will study three types of milling machines, which include plain milling machine, vertical milling machine and universal milling machine, then study these three milling machines one by one.
Also read this – Concept of milling machine working principle
Plain milling machine
1. Base and Column : It is the main casting of the machine and is a box like casting that rises from a base which rests on the floor. The hollow base serves as a tank for the cutting fluid supply for the machine. An individually motor driven pump circulates the cutting fluid through piping to the place of milling operation on the machine.
The electric motor that drives the machine spindle and the change gears for the power feed is generally housed in the lower part of the column. The upper part of the column serves as a housing for the spindle and set of change gears that drive the spindle. The top of the column is finished to hold an over arm.
The front of the column is called face. This face is machined to provide a plane surface as ways at 90 degrees to the axis of the spindle that serve as the mounting which support the knee.
2. Knee : It is a casting which is supported on the ways on the face of the column, It is raiscd or lowered with an elevating screw to adjust height of the work pieces relative to milling cutters when setting up the jobs or to provide a hand or power operated vertical feed cutting.
After adjusting the knee to the required height, it is clamped in position so that it does not shift while machine is in operation. The top of the knee is finished to provide horizontal ways on which a saddle is mounted.
3. Saddle : It is a casting which is mounted on the top of the knee. It is adjustable on ways on the top of the knee through hand wheel or power feed, towards or away from the column to provide cross feed. The top of the saddle is finished to form ways in which a table is supported. The saddle may also be clamped in position during cutting operations to provide rigidity.
4. Table : It is a rectangular casting that is supported on top of the saddle. It possesses T-slots running the full length of its top to provide a horizontal surface on which work pieces and work-holding devices are fastened with T-bolts and other holding accessories.
The table can be fed longitudinally through a handwheel or power drive parallel to the face of the column. The table may also be clamped in position during cutting operations to provide rigidity.
5. Overarm: The top of the column is finished to hold an overarm that extends outwards at the front of the machine, The overarm consists of one or two heavy round bars or a bar that is generally rectangular in section. To support the arbor properly, the overarm can be moved in or out of the column to the required length.
There is arrangement to clamp the overarm in any position. The braces from the table often support the overarım, especially during heavy cuts, to give it added rigidity to achieve better accuracy of the work.
6. Spindle : It is placed in bearings inside the column. Its outer end just projects from the column face and is provided with a tapered hole and driving keys for locating and driving the cutters. End mill type of cutters can be directly inserted in the spindle. Other cutters have to be mounted on the arbor and the arbor is driven by the spindle.
7. Arbor : It is an accurately machined shaft for holding and driving the cutters. It is tapered at one end to fit in the hole of the spindle, When in position in the spindle, a drawbolt is threaded into its end from the rear of the machine.
This keeps the arbor tightly in its place. Its other end is supported by an overarm support (yoke), in a proper bearing, except for stub arbors. It possesses a keyway running along its length and is supplied with several collars or spacers which space the cutter exactly where desired. The use of very thin shims is made to position the cutter precisely.
vertical milling machine
A vertical milling machine with principal parts labelled. This is of the type having swiveling spindle head. The spindle head of a vertical milling machine may also be of fixed type. The special feature of this type of milling machine is the vertically mounted milling spindle in the milling head.
The main and the feed drives do not differ from those of the plain milling machine. This machine is also provided with a short axial spindle travel to facilitate step milling.
Some vertical milling machines are provided with rotary attachments or rotating work tables to facilitate the milling of circular grooves or continuous milling of small production parts. Cutters used are all of the end-mill type.
universal milling machine
shows diagrammatically a universal milling machine with principal parts labelled. It differs from a plain milling machine in that its table ways are contained in a swivel base saddle plate that is mounted on a circular seat on the top of the saddle. This arrangement permits the table to be swiveled at an angle in the horizontal plane when the machine is set for helical milling.
The table of this type of milling machine is always provided with a dividing bead. As compared to vertical milling machine, the universal milling machine spindle is normally horizontal but it can perform the function of vertical milling machine with the help of vertical milling attachment.
The table of the universal milling machine can be swiveled where as that of vertical milling machine does not have this provision. A modified form of this machine is called an universal milling machine. This machine is provided an additional adjustment so that the table may be tilted and, in that position, fed horizontally.
Another type of universal machine is known as ram type universal milling machine. It carries a ram on the top of the column. The cutter head is pivoted to the face of the ram and is capable of any angle adjustment between vertical and horizontal.
The ram, which carries the cutter head, is provided with an in and out movement over the work table. With the combined adjusting feature of cutter bead, ram, and work table, it is possible to do conventional horizontal, angular or vertical milling.
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