Manufacturing Processes lab I Running a lathe machine-2

Cutting speeds and feeds:

These factors govern the length of time required to machine the work and the quality of the surface finish.

Various Cuts:

Roughing cuts are taken to reduce work diameter to approximate size. The work is left 1/32” (0.08 mm) oversize for finish turning. (use the highest speed and coarsest feed consistent with safety and accuracy).

Finishing cut brings the work to the required diameter and surface finish. A high-spindle speed, sharp cutting tool and fine feed are employed.

Cutting Speed:

Cutting speed, indicates the distance the work moves past the cutting tool, expressed in feet per minutes (fpm) or meters per minutes (mpm).

In fact, the length of the chip cut in one minute (in feet or meters) would be the cutting speed of the lathe.

Cutting speed is not the revolutions per minute (rpm) of the lathe.

Cutting Feed:

Feed is the distance that the cutter moves length-wise along the lathe bed during a single revolution of the work.

Cutting speeds and feeds suggested for turning various metals with high-speed steel tools.

These speeds will be increased by 50% if a coolant is used, and by 300% to 400% if a cemented carbide cutting tool is employed.

Calculating cutting speeds:

Cutting speed (CS) is given in feet per minute (fpm) or meters per minute (mpm).

Speed of the work (Spindle speed) is given in revolutions per minute (rpm).

The peripheral speed (speed at the circumference or outside edge of the work) must be converted to rpm to determine the required spindle speed.

INCH-BASED: CS=Cutting Speed, in feet/min

D= Diameter of work in inches

Convert all fractions to decimals

Round π to 3

Rpm=(CS*12)/ ΠD=(CS*4)/D

Calculating cutting speeds:

What spindle speed is required to finish-turn 8” diameter aluminum alloy?

rpm= (CSx 4/D)=

1000”x4/8= 500 rpm

So adjust the spindle speed to as close to 500rpm as possible. Increase or decrease speed as needed to obtain desired surface finish.

METRIC-BASED:

Rpm= (CS*1000)/ π D

CS=Cutting Speed in meter.

D= Diameter of work in milimeter .

round π to 3

rpm= (300mpmx 1000)/ (100 π)=

3000/3= 1000 rpm

Depth of Cut:

The depth of cut refers to the distance the cutter is fed into the work surface. The depth of cut, like feed, varies greatly with lathe condition, material hardness, speed, feed, amount of material to be removed and whether it is to be a roughing or finishing cut.

Depth of cut can be set accurately with the Micrometer dials on the cross-slide and compound rest.

The micrometer dial is usually graduated in 0.001” or 0.02mm increments.

This means that a movement of one graduation feeds the cutting tool into the piece 0.001” or 0.02mm. However, material is removed around the periphery (outside edge) of the rotating work at double the depth adjustment.