Column and Knee Type Milling Machine
Column and Knee Type Milling Machine: Fig. 1 shows a simple column and knee type milling machine. It is the most commonly used milling machine used for general shop work. In this type of milling machine the table
Fig. 1 A column and knee type milling machine
column. The knee is vertically adjustable on the column so that the table can be moved up and down to accommodate work of various heights. The column and knee type milling machines are classified on the basis of various methods of supplying power to the table, different movements of the table and different axis of rotation of the main spindle. Column and knee type milling machine comprises of the following important parts-
1. Base, 2. Column, 3. Saddle, 4. Table, 5. Elevating screw, 6. Knee,7. Knee elevating handle, 8. Cross feed handle, 9. Front brace, 10. Arbor support, 11. Arbor 12. Overhanging arm, 13. Cutter, 14. Cone pulley, 15. Telescopic feed shaft.
The principal parts of a column and knee type milling machine are described as under.
Base: It is a foundation member for all the other parts, which rest upon it. It carries the column at its one end. In some machines, the base is hollow and serves as a reservoir for cutting fluid.
Column: The column is the main supporting member mounted vertically on the base. It is box shaped, heavily ribbed inside and houses all the driving mechanism for the spindle and table feed. The front vertical face of the column is accurately machined and is provided with dovetail guideway for supporting the knee.
Knee: The knee is a rigid grey iron casting which slides up and down on the vertical ways of the column face. An elevating screw mounted on the base is used to adjust the height of the knee and it also supports the knee. The knee houses the feed mechanism of the table, and different controls to operate it.
Saddle: The saddle is placed on the top of the knee and it slides on guideways set exactly at 90° to the column face. The top of the saddle provides guide-ways for the table.
Table: The table rests on ways on the saddle and travels longitudinally. A lead screw under the table engages a nut on the saddle to move the table horizontally by hand or power. In universal machines, the table may also be swiveled horizontally. For this purpose the table is mounted on a circular base. The top of the table is accurately finished and T -slots are provided for clamping the work and other fixtures on it
Overhanging arm: It is mounted on the top of the column, which extends beyond the column face and serves as a bearing support for the other end of the arbor.
Front brace: It is an extra support, which is fitted between the knee and the over-arm to ensure further rigidity to the arbor and the knee.
Spindle: It is situated in the upper part of the column and receives power from the motor through belts, gears. and clutches and transmit it to the arbor.
Arbor: It is like an extension of the machine spindle on which milling cutters are securely mounted and rotated. The arbors are made with taper shanks for proper alignment with the machine spindles having taper holes at their nose. The draw bolt is used for managing for locking the arbor with the spindle and the whole assembly. The arbor assembly consists of the following components.
1. Arbor 2. Spindle, 3. Spacing collars 4. Bearing bush, 5. Cutter 6. Draw bolt, 7. Lock nut 8. Key block, 9. Set screw
Planer Type Milling Machine: It is a heavy duty milling machine. It resembles a planer and like a planning machine it has a cross rail capable of being raised or lowered carrying the cutters, their heads, and the saddles, all supported by rigid uprights. There may be a number of independent spindles carrying cutters on the rail as two heads on the uprights. The use of the machine is limited to production work only and is considered ultimate in metal re-moving capacity.
Special Type Milling Machines: Milling machines of non-conventional design have been developed to suit special purposes. The features that they have in common are the spindle for rotating the cutter and provision for moving the tool or the work in different directions.