Conventional Mill Operation

Crash Course in Milling, Chapter 2 - Conventional Mill Operation, by Glacern Machine Tools from Glacern Machine Tools on Vimeo.

Conventional Milling Machine

The Milling Machine uses a rotating milling cutter to produce machined surfaces by progressively removing material from a work piece. The vertical milling machine also can function like a drill press because the spindle is perpendicular to the table and can be lowered into the work piece.

THE CONTROLS START/STOP The green button starts the spindle motor and the red button shuts the motor off. Variable Motor Drive used on some of the Milling Machines FORWARD/REVERSE This switch changes the rotation direction of the spindle. When the milling machine is in high range this switch is in the forward position for cutting but in low range the switch is in the reverse position. Putting the switch in the opposite position while remaining in the same range reverses the rotation of the spindle. HAND BRAKE Also known as the spindle brake, it is used to bring the spindle rotation to a stop after the power is turned off and to aid in removing collets and chucks. The spindle can be locked by pressing or pulling the brake and then pushing it up. SPINDLE SPEED This wheel is used to change the speed of the spindle for both high range and low range. The milling machine must be running when changing the speed. POWER FEED The power feed uses a motor to control the motion of the longitudinal feed in either direction at various speeds. Not all of the milling machines in the shop have this option. CROSS-FEED HANDWHEEL This handwheel moves the table in and out. VERTICAL FEED HANDCRANK This is used to raise and lower the table. LONGITUDINAL HANDWHEEL This handwheel moves the table left and right. On some machines the handles are spring activated to keep them from rotating when the power feed is used. HIG-LOW SPEED CONTROL The high-low speed switch changes the range from high to low and vise-versa. The spindle may need to be turned by hand while engaging the gears. QUILL FEED HANDLE You can raise and lower the quill (spindle) with this handle. QUILL LOCK Pushing this lever down will lock the quill, pulling it back up releases the lock. The quill must be locked when milling. QUILL STOP The quill stop can be adjusted by hand to set a limit on the quill travel is also used to disengage the quill feed. This is useful when multiple holes have to be drilled to the same depth. QUILL FEED LEVER AND SELECTOR These are used to activate the power feed for the quill. The selector will adjust the speed of the power feed and the lever activates the drive. The quill feed can

DIGITAL READOUT These readouts were added to the milling machines to aid in the accuracy of cuts and increase productivity. The lateral movement of the table can be measured to 2/10,000th of an inch with the readouts. Other operations the readout can perform include dividing any dimension by two, running with absolute or relative measurements, and displaying in inches or millimeters.

LONGITUDINAL/CROSS-FEED AXIS The digital readout will display the distance traversed in both the X and Y axis. ZERO BUTTONS These two buttons will set their respective displays to zero. This is used after the machinist finds the edge of their part and wants to reference all of the other measurements off that axis. INCHES/METRIC BUTTON The readout can give all measurements in inches or millimeters, by pressing this button it will switch from one system of measurement to the other. KEYPAD Dimensions can be entered into the readout using the keypad. This can be helpful when a reference point is needed other than zero.

Peripheral and Face Milling Techniques

Fig. 1

Peripheral milling uses teeth on the outer edge of the cutter body. The surface produced corresponds to the contour of the milling cutter, which can range from a flat surface to a formed shape. There are two different methods of peripheral milling, Conventional or Up Milling and Climb or Down Milling. The figures on the left show the rotation of the cutting tool with respect to the direction of the part on the table. In conventional milling the work is fed against the cutter which compensates for backlash in the table. Each tooth of the cutting tool starts its cut in clean metal, prying the material off the work. Down milling will give a better quality of work and is better suited for thin pieces of material since the cutting action forces the work into the table. This method should not be used on hard materials and the machine has to be rigid so backlash cannot occur. The cutting tool will also last longer using Down milling as long as good tool pressure is maintained. The machines in the shop are suitable for both types of milling. If you are unsure of which method you should use ask somebody in the shop for assistance. Face milling uses the bottom of the mill to machine the work instead of the sides. The cutting comes from the combined action of cutting edges located on the face (or end) of the cutting tool as well as the edges on the periphery. The direction of the feed with relation to the rotation is not important when using this method.