How to choose the cutting amount

Reasonable cutting amount is one of the important prerequisites for scientific management of production and high technical and economic indicators. Today, I will introduce the general selection method of cutting amount of commonly used processing methods.

1.The choice of turning amount

(1) The amount of knives used on the back

During rough machining, all machining allowances should be cut off at one time as much as possible, that is, the value of the back-feeding knife should be selected to be equal to the allowance value. When the margin is too large, the rigidity of the process system and the effective power of the machine tool should be considered, and a larger value of the back engagement knife and a smaller number of working strokes should be selected as much as possible.

During semi-finishing, if the unilateral allowance h>2mm, it should be cut in two strokes:

The first time a=(2/3~3/4)h, the second time a=(1/3~1/4)h. If h≤2mm, it can be removed at one time.

When finishing, the finishing allowance should be removed in one stroke.

(2) Feed amount

After the back cut amount is selected, the feed amount directly determines the cutting area, and the cutting force is determined from the surface.

The maximum allowable feed is limited by the following factors: 

a, the effective power and torque of the machine tool;

b, the strength of the transmission chain of the machine tool feed mechanism;

c, the stiffness of the workpiece;

d, the strength and stiffness of the tool;

e, the machined surface roughness specified in the drawing.

Most of the actual production relies on experience. The inexperienced can use the metal cutting quantity manual to check the table to determine the feed rate.

(3) Cutting speed

To determine the cutting speed, the general method is to select the v value according to a reasonable tool life calculation or look-up table.

When finishing, the cutting speed as high as possible should be selected to ensure the machining accuracy and surface quality and meet the requirements of productivity.

When roughing, consider the following:

a, The average cutting speed of carbide turning tool for hot-rolled medium carbon steel is 1.67m/s,

   The average cutting speed of gray cast iron is 1.17m/s,

   The average tool life of the two is 3600~5400s.

b. The cutting speed of cutting alloy steel is 20%~30% lower than that of cutting medium carbon steel;

c. The cutting speed of steel in quenched and tempered state is 20%~30% lower than that of steel in normalized and annealed state;

d, the cutting speed of cutting non-ferrous metals can be increased by 100%~300% compared to cutting medium carbon steel

2.The choice of milling amount

(1) Amount of cutting tool for milling back

Rough milling, the amount of back cut is equal to the machining allowance, and the milling is completed in one working stroke. 

Semi-finishing and finishing, usually in two steps,

During semi-finish milling, the amount of back cutting is generally 0.5~2.0mm; 

During fine milling, the cutting amount of the milling back is generally 0.1~1.0mm or less

(2) Feed per tooth

It is found in the cutting quantity manual, in which the recommended values have a range.

When the fine milling or milling cutter diameter is small and the milling cutting amount is large, the smaller value is used.

A large value is often used for rough milling.

When machining iron castings, use medium and large values

Use the smaller value when machining steel

(3) Milling speed

Appropriately select a higher cutting speed. Calculate according to the formula or check the cutting quantity manual.

For large plane milling, use a dense-tooth milling cutter, select a large feed, and perform high-speed milling.

3. Selection of planing amount

(1) The amount of knives used for planing the back

Basically the same as turning

(2) Feed amount

Select according to the recommended value of turning feed in relevant manuals.

The rough planing plane is selected according to the cutting amount and the cross-sectional size of the tool bar, and the larger value is selected according to the outer circle of the rough turning.

Finishing is selected according to semi-finishing and finishing outer circle

Grooving and cutting are selected according to the turning and cutting feed.

(3) Planing speed

Choose based on practical experience. 

It can also be calculated according to the turning speed formula, and the impact load should be considered, and the correction coefficient k should be introduced.

4.The choice of drilling amount

The selection of drilling amount includes determining the drill diameter D, the feed amount f and the cutting speed v (or the spindle speed n)

Choose a drill with a large diameter as much as possible, choose a large feed, and choose the drilling speed according to the life of the drill.

(1) Drill diameter 

Determined by the process size requirements, drill the required holes at one time as much as possible.

When the performance of the machine tool is not sufficient, the process of selecting drilling and then expanding the hole is adopted. At this time, the diameter of the drill bit is 0.5~0.7 times of the processing size.

The diameter of the twist drill for holes can be selected from JB/Z228~1985.

(2) Feed amount 

The feed rate must be determined according to practical experience and specific conditions.

The feed rate of the standard twist drill can be selected from the table

It is limited by the amount of drilling back and the feed mechanism and power of the machine tool, and also limited by the rigidity of the process system.

(3) Drilling speed

According to the life of the drill bit, choose according to experience