How to Accurately Control The Taper of Outer Circle Machined by Lathe?

This post introduces the precise control method of cylindrical taper machined by horizontal lathe.

Firstly, the trigonometric function relationship is used for data calculation, and then the dial indicator is used to detect the half angle of the cone.

Finally, through simulation processing, the angle of the small sliding plate is intuitively adjusted to the correct position, so as to achieve the purpose of accurately controlling the cone angle.

1. Preamble

Taper is widely used in mechanical matching and assembly.

If the designer gives the taper size of the inner hole and requires to process the outer cone to match it, it is quite difficult for the operator because the taper of the outer cone is not easy to control and measure.

The machining equipment in the main plant area of Panzhihua Iron and Steel Co., Ltd. are c6120 and CA6140.

When turning a cone with a small sliding plate, the minimum deflection accuracy of the lathe is 1 °, and it is difficult to meet the matching requirements for the machining of outer cone with high precision.

Next, use other measuring instruments to control the taper of the cone by relative measurement method, so as to meet the matching requirements.

2. Manual turning of short conical small sliding plate

The parts shown in Fig. 1 are mainly composed of cone and thread.

Manual turning of short conical small sliding plate

Fig. 1 parts

The main dimensions of the cone are shown in Fig. 2, mainly including:

Manual turning of short conical small sliding plate

Fig. 2 main dimensions of conical part

① Cone angle α, is the angle between two prime lines.

② Cone half angle α/ 2, that is, the rotation angle of the small sliding plate during turning.

③ Maximum end diameter D, referred to as large end diameter.

④ Minimum end diameter d, referred to as small end diameter.

⑤ Cone length L, that is, the distance between the large end diameter and the small end diameter on the axis.

When turning taper, the rotation angle of small sliding plate is α/ 2, as shown in Fig. 3.

Schematic diagram of rotation angle of small sliding plate

Fig. 3 Schematic diagram of rotation angle of small sliding plate

Small sliding plate rotation α/ 2 angle, according to the trigonometric function relationship, tan( α/ 2)=(D-d)/(2L)=(40-20)/(2 × 50) = 0.2, available α/ 2=11°20′.

That is, the rotation angle of the small sliding plate is 11 ° 20 ‘, and the rotation angle division of the small sliding plate is 1 ° one grid, which is not subdivided into 20’.

The small sliding plate can only be adjusted by measuring with a universal angle ruler, which is not only time-consuming and laborious, but also the cone angle turned out is inaccurate.

The accuracy of the workpiece is not high, and it is difficult to meet the matching requirements.

In order to solve this problem, analyze the shaded right triangle in Fig. 2 (see Fig. 4).

Fig. 4 Shaded right triangle

When turning the taper, the turning tool travel path is from point C to point B.

The length of the turning tool travel path can be calculated according to the Pythagorean theorem (see Fig 5).

Fig. 5 Length of turning tool travel path

During turning, the distance of the tool tip from point C to point B can be controlled by the dial of the small sliding plate.

When the turning tool moves 50.99mm, the distance between the tool tip and the axis line of the lathe is just 10mm, which proves that the conical angle of turning is correct;

Otherwise, the rotation angle of the small sliding plate is incorrect.

Before machining taper, you can simulate machining first.

After rotating the small sliding plate, first shake the small sliding plate by 50.99mm, and then use a measuring tool to monitor whether the distance between the tool tip and the axis line of the lathe is 10mm, so as to know whether the rotation angle of the small sliding plate is correct.

Through this method, the angle of the small sliding plate can be adjusted intuitively until the cone angle is correct.

The specific operation method is shown in Fig. 6.

Schematic diagram of specific operation method

Fig. 6 Schematic diagram of specific operation method

1) Finish turning a section of outer circle first, the surface roughness value shall be small, and there shall be no taper on the length of the cylinder.

The two ends of the cylinder can be measured with a micrometer. If the dimensions of the cylinders at both ends are the same, it means that the cylinder has no taper.

2) Calculate the movement of the dial indicator, and calculate the BC side length according to the Pythagorean theorem, which is exactly the length that the small sliding plate needs to walk when the car is tapered (BC = 50.99mm).

3) Move the small sliding plate counterclockwise to 11 ° ~ 12 °, lock any screw of the small sliding plate, then suck the base of the dial indicator on the tool holder of the small sliding plate, and push the contact of the dial indicator on the outer circle (see Fig. 6).

4) Align the small sliding plate with the zero position, point the dial indicator to the scale position of 10mm, move forward to the small sliding plate, and the contact of the dial indicator will extend slowly.

When the small sliding plate moves 50.99mm and the moving distance of the dial indicator is less than 10mm, it indicates that the taper is small.

At this time, loosen the locking screw and increase the taper;

When the small sliding plate moves by 50.99mm and the moving distance of the dial indicator is more than 10mm, it indicates that the taper is large, and the taper should be reduced at this time;

When the small sliding plate moves 50.99mm and the dial indicator moves 10mm, it indicates that the taper at this time is correct and turning can be carried out.

Precautions during adjustment are as follows:

1) The outer circle used to determine the taper cannot have the taper phenomenon itself, otherwise the determined taper will be inaccurate.

If the turned outer circle has a taper, press the dial indicator against the tailstock sleeve to align the taper.

2) The magnetic base of dial gauge shall be firmly absorbed, and the connecting rod screw on the gauge frame shall be tightened without loosening.

3) The measuring rod of the dial indicator shall be perpendicular to the axis of the outer circle.

If necessary, a small square can be used to correct the perpendicularity, and the contact of the measuring rod of the dial indicator shall be on the bus near the axis of the outer circle as far as possible.

4) The measuring stroke of the dial indicator should be as large as possible.

There are many ranges of 10mm. If necessary, one range of 30 ~ 50mm can also be prepared.

5) This method can also be used when machining inner cone.

3. Automatic tool walking turning of long conical saddle

As shown in Fig. 7, the turning taper of the automatic tool feeding of the saddle is actually the taper processed by the offset tailstock method.

Turning taper of automatic tool feeding of saddle

Fig. 7 Turning taper of automatic tool feeding of saddle

After the tailstock of the lathe is offset laterally for a certain distance s, the rotation axis of the workpiece intersects with the spindle axis of the lathe, and the included angle = the half angle of the workpiece taper α/ 2.

Since the bed saddle is fed parallel along the main axis, the car becomes a taper.

This method is suitable for workpieces with small taper (taper < 3 °) and long length.

3.1 Calculation of tailstock offset s

Tailstock offset S ≈ L0tan( α/ 2) = L0 (D-d) / (2L) or S = CL0 / 2, where,

  • S is the tailstock offset (mm);
  • D is the maximum cone diameter (mm);
  • D is the minimum cone diameter (mm);
  • L is the cone length (mm);
  • L0 is the total length of the workpiece (mm);
  • C is taper.

For example, machining a cylindrical taper workpiece between two centers, knowing D = 80mm, d = 76mm, L= 600mm, L0 = 1000mm, calculate the offset S of the tailstock.

According to the formula, the solution is S = L0 (D-d) / (2L) = 1000 × (80-76)/(2 × 600)=3.3(mm).

3.2 Offset measurement of tailstock

Install a dial indicator on the tool holder to measure the offset of the tailstock (see Fig. 8).

Figure 8 Offset measurement of tailstock

3.3 Turning steps

The automatic tool feeding of the bed saddle is used to process the cone.

The clamping of the workpiece is shown in Fig. 9.

The rough turning outer cone is shown in Fig. 10, and the fine turning outer cone is shown in Fig. 11.

Clamping of workpiece

Fig. 9 Clamping of workpiece

Rough outer cone

Fig. 10 Rough outer cone

Finish turning outer cone

Fig. 11 Finish turning outer cone

3.4 Characteristics of turning outer cone with automatic tool feeding of bed saddle

1) It is suitable for processing outer conical workpieces with small taper (taper < 3 °) and long cone.

Due to the limitation of tailstock offset, workpieces with large taper cannot be processed.

2) The bed saddle can be fed longitudinally automatically to reduce the surface roughness Ra and improve the surface quality of the workpiece.

3) Because the tip is skewed in the center hole and has poor contact, the wear of the tip and the center hole is uneven.

4) Because the workpiece is clamped with double apices and the chicken heart clamp transmits power, the inner cone and the overall outer cone cannot be machined.

4. Conclusion

The above two methods of machining cone make full use of the trigonometric function relationship for data calculation, and then indirectly adjust the cone half angle through the dial indicator, so as to achieve the purpose of turning the outer cone and improve the accuracy of the cone half angle of the workpiece.

These two methods have popularization significance in machining outer cone with ordinary machine tools.

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