What is a movable turning steady rest? This question can take by surprise only people who are far from the world of machine tools. Any turner (even a beginner) knows what this device is intended 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 describes the characteristics of steady rests for lathes, describes the features and scope of their application.
Structure and design features of lunettes
There are fixed and movable steady rests for lathes. Stationary rests are rigidly fixed to the guides of the lathe bed and do not move during operation. As the name implies, steady rests can move along the axis of rotation along with the movement of the tool holder and carriage.
Besides, rolling rollers or fixed cams can be used as supports in steady rests. Both rollers and fixed cams have their advantages and disadvantages. So, the rollers will not damage the material of the workpiece and do not wear out. However, they (especially after long-term operation) can work with a runout, which cannot but affect the processing parameters. Therefore, for precision machining of small diameter workpieces, it is recommended to use steady rests with cams rather than rollers.
Not to mention the so-called shoes. This is the name of the lunette of a special design. Its scope is the processing of long workpieces on cylindrical grinding machines.
The most common steady rests with manual movement and locking of the cams. It is this equipment that is supplied with all universal machines (16K20, 1K62, 1M63). Mobile steady rests of lathes with numerical control of domestic (16B16F1, 16K20F1) and foreign ("Mazak", "Okuma", "Haas" and so on) are equipped with self-centering steady rests with a hydraulic drive. When working with such equipment, the operator of the machine just needs to press the pedal, and the automation will do the rest.
What are the advantages of using a steady 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, in its absence, the part can simply bend and break the cutter. It is also possible to damageequipment and injury to the workers of the shop.
In addition, the use of a steady rest allows you to increase the accuracy of processing by an order of magnitude, increase the cutting speed (increased labor productivity), and increase tool life.
Installation and adjustment of steady rests
You can set the device in several ways: using a workpiece and a stand with a micrometer.
It is possible to install a steady rest on the workpiece only if the workpiece, fixed in the centers, does not have significant geometric deviations. In other words - after preliminary turning. In all other cases, the fixture is set using high-precision measuring instruments.
In real production conditions, a situation often arises when the equipment needs to be adjusted even before the workpiece is fed. In such cases, the movable rest is installed along a bar, the diameter of which is equal to the diameter of the future part. Such a bar is clamped in the chuck from the side of one end, and from the other side it is necessary to dust the diameter (that is, remove a slight allowance with a turning tool). On the resulting clean surface, the rollers of the lunette are exposed.
Some features of steady rest operation
One end of the workpiece is clamped into a three-jaw self-centering lathe chuck (can be a collet, driver chuck or other device), and the other is supported by the center of the tailstock. The workpiece is in contact with three cams or rollers. Wherein,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 the cams of the movable steady rest is, as a rule, cast iron. This alloy has good anti-friction properties, but there is still a risk of damaging soft annealed steel workpieces. Therefore, it is recommended to install nozzles made of bronze or babbitt on the cams. This will remove the finish surface of the responsible product from scratches and abrasion. If it is not possible to manufacture 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 in question is processed on the machine, then you can not be afraid of damage.
Movable steady rest 16К20
This type of lunette has some design features. So, it is attached directly to the caliper of the machine. Special threaded connections are provided for this.
The body is usually 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 factories produce many modifications of such lunettes. They differ slightly. The main indicators are unchanged: the minimum processing diameter is 110 or 150 millimeters.
Movable steady rest 1К62
Included with the universal screw-cutting lathe 1K62 are two steady rests (fixed and movable).
The steady rest has a lid. It is attached to the base with a screw connection. There are grooves on the bottom. In shape, they are identical to the guides of the machine bed, thanks to which it is possible to fix the steady rest well and exclude movement along any axes. Allows processing of bars and other bodies of revolution with a diameter of 20 to 130 millimeters.
Movable steady rest allows to process products with a diameter of 20 - 80 millimeters. Thus, the steady rest significantly expands the technological capabilities of machine tools (after all, without it, the minimum machining 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 lunettes are still made by many tool and machine tool factories. That says a lot.
Conclusion
When cutting metals and steels, vibrations occur that adversely affect both the quality of the surface being machined and the performance of equipment and tools. This problem is especially acute when processing long workpieces (length to diameter ratio of 10:1 or more). To solve the problem of vibrations and the risk of injury to the worker allows a special device - a turning movable steady rest.
