What is a mobile lathe? This question can be taken aback only by people far from the world of machine tools. Any turner (even a beginner) knows what this device is for. It should be noted that such devices are used not only in turning, but also in the processing of parts on milling, grinding and other machines. The article gives a description of mobile lunettes for lathes, describes the features and their scope.
The structure and design features of the lunettes
There are fixed and movable lunettes for lathes. Fixed lunettes are rigidly fixed to the guides of the lathe bed and do not move during operation. As the name implies, movable lunettes can move along the axis of rotation along with the movement of the tool holder and the carriage.
In addition, rolling rollers can be used as supports in lunettes, and stationary cams can also be used. Both rollers and fixed cams have their advantages and disadvantages. So, the rollers will not damage the workpiece material and will not wear out. However, they (especially after prolonged use) can work with beating, which cannot but affect the processing parameters. Therefore, for precision machining of small diameter workpieces, it is recommended to use movable lunettes with cams rather than with rollers.
It is impossible not to mention the so-called shoes. This is the name of a special design lunette. Its field of application is the processing of long workpieces on circular grinding machines.
The most common lunettes with manual movement and fixation of the cams. It is this kind of equipment that comes complete with all universal machines (16K20, 1K62, 1M63). Movable lunettes of lathes with numerical control of domestic (16B16F1, 16K20F1) and foreign (Mazak, Okuma, Haas and so on) are equipped with self-centering lunettes with a hydraulic drive. When working with such equipment, it’s enough for the machine operator to press the pedal, and the rest will be done by automation.
What are the advantages of using the rest in the processing of long workpieces?
You can do without a lunette. However, in the case of processing long bodies of revolution with a small cross-sectional area if it is absent, the part can simply bend and break the cutter. It may also damage equipment and injure workers in the workshop.
In addition, the use of a lunette allows an order of magnitude to increase the accuracy of processing, increase the cutting speed (labor productivity increases), and increase the tool life.
Installation and configuration of lunettes
The device can be set in several ways: using a workpiece and a stand with a micrometer.
It is possible to install a moving rest on the workpiece only when the workpiece fixed in the centers does not have significant geometric deviations. In other words, after preliminary turning. In all other cases, the device is exposed using high-precision measuring instruments.
In the context of real production, a situation often arises when equipment needs to be adjusted before the workpiece is fed. In such cases, the movable lunette is installed on a bar whose diameter is equal to the diameter of the future part. Such a rod is clamped in the chuck from the side of one end, and from the side of the other it is necessary to dust the diameter (that is, remove a slight allowance with a turning tool). On the resulting clean surface, the lunette rollers are exposed.
Some features of the operation of lunettes
One end of the workpiece is clamped into a three-jaw self-centering turning chuck (it can be a collet, a chuck or other device), and the other is propped up by the center of the tailstock. The workpiece contacts three cams or rollers. Moreover, if the workpiece is not accurate (casting or forging), then the contact point of the rollers and cams with the part must be read.
The material for the manufacture of cams of a movable lunette is, as a rule, cast iron. This alloy has good antifriction properties, but there is still a danger of damaging mild annealed steel workpieces. Therefore, it is recommended to install nozzles made of bronze or babbits on the cams. This will remove the scratched surface and abrasion of the critical surface of the critical product. If it is not possible to make such nozzles, then preference should be given to rolling rollers. This will prevent damage to the surface of the part. However, if subsequently the surface of the product under consideration will be processed on the machine, then you can not be afraid of damage.
Mobile rest 16K20
This type of lunette has some design features. So, it is attached directly to the support of the machine. For this, special threaded connections are provided.
The case, as a rule, is cast from gray cast iron. Otherwise, everything is standard - three cams or rollers that are in contact with the workpiece, grooves in the form of guides on the bed.
Machine-tool plants produce many modifications of such lunettes. They differ slightly. The main indicators are unchanged: the minimum processing diameter is 110 or 150 millimeters.
Mobile rest 1K62
Included with the universal screw-cutting machine 1K62 there are two lunettes (fixed and movable).
The fixed lunette has a lid. It is attached to the base with a screw connection. There are grooves on the bottom. They are identical in shape to the guides of the machine bed, due to which it is possible to fix the lunette well and to exclude movement along any axes. Allows you to process bars and other bodies of revolution with a diameter of 20 to 130 millimeters.
The mobile rest allows you to process products with a diameter of 20 - 80 millimeters. Thus, the lunette significantly expands the technological capabilities of the machine tool equipment (after all, without it, the minimum processing diameter is 40 millimeters). It is very important. There are certain restrictions on the frequency of rotation of the spindle (and hence the workpiece). So, the maximum rotation speed is 2000 rpm, and the minimum is 12.5 rpm.
Machines of this type have not been produced for a long time and are considered obsolete. But the lunettes are still manufactured by many tool and machine tool factories. That says a lot.
Conclusion
When machining metals and steels by cutting, vibrations occur that adversely affect both the quality of the surface being treated and the performance of equipment and tools. This problem is especially acute when machining long workpieces (length to diameter ratio of 10: 1 or more). To solve the problem of vibration and the risk of injury to the worker allows a special device - a turning mobile rest.