The back grandmother is a critically important node of the lathe, responsible for reliable fixation of long blanks and placement of a cutting tool for drilling holes. Without this element, it is impossible to perform accurate processing of complex shaped parts, since it ensures the rigidity of the structure and prevents the shaft from beating at high revs. Understanding the principle of operation of this mechanism is necessary for each operator of CNC machines and turning machines.
Structurally, this unit is a cast iron or steel base that moves along the guides of the machine. Depending on the equipment, whether 16K20 or more modern modifications, the design may have its own features, but the functional purpose remains unchanged. The operator must be able not only to move the node, but also to correctly center it relative to the spindle axis.
Incorrect configuration of this unit leads to cone-like surfaces and rapid wear of the cutting tool. Adjustment of gaps in the guides and checking the axis of the spindle of the grandmother with the axis of rotation of the cartridge are mandatory procedures when setting up the equipment. Ignoring these requirements reduces the quality of products and can cause a defect in serial production.
The design and main elements of the node
The basis of the mechanism is the body, inside which are the guides, along which the moving part - pinol moves. pinol It is a hollow shaft that is pushed forward when the flywheel is rotated. The inner pinoli hole has a standard Morse cone, which allows you to install various types of tools: drills, zenkers, sweeps or a fixed center to support the workpiece.
A special clamping mechanism is used to fix the position of the node on the wall. Older models often used eccentric clamps, which required considerable physical effort, whereas modern machines are equipped with hydraulic or pneumatic clamps. PlateThe groove on which the grandmother is mounted has T-shaped slots for installing additional devices or stops.
- 🔧 Corps - cast base, ensuring the rigidity of the entire structure.
- 🔧 pinol A movable shaft for mounting a tool or center.
- 🔧 flywheel - handle for manual movement of pinoli.
- 🔧 The locking mechanism - a device for fixing the grandmother on the wall.
It is important to note that the inner surface of the pinoli is carefully polished and often subjected to heat treatment to improve wear resistance. Luft in this node is unacceptable, as it directly affects the accuracy of the depth of drilling. Some models of machines have a pinoli limiting mechanism, which is set up by the operator before starting work.
Principle of operation and functionality
The main task of the back grandmother is to create a second support for long shafts, which excludes their deflection under the action of cutting force. When the workpiece is clamped in the cartridge at one end, and the other rests on the center of the grandmother, the system becomes statically definable and stable. This allows you to remove large metal drops without the risk of deformation of the part.
The second important function is to perform drilling operations. The operator can install the drill into the pinoli cone and, rotating the flywheel, apply the tool to the rotating workpiece. The feed rate is adjusted manually or, in automated systems, through the servo. The axis of rotation Pinoli should be perfectly coaxial with the axis of the spindle of the main grandmother.
⚠️ Attention: Before drilling, make sure that the center or tool is securely fixed in the cone. The departure of the tool should be minimally necessary to reduce the risk of failure.
There are also rotary money, which allow you to shift the pinoli axis in the horizontal plane. This function is used to sharpen conical surfaces. The angle of rotation is set on a scale on the upper plate and is fixed by special screws. The accuracy of the angle setting directly affects the cone of the resulting part.
Types of back dough and their features
In metalworking, several types of nodes are used, which differ in the method of control and design. Mechanical cash is manually controlled by the operator through a flywheel and a screw gear. They are easy to maintain, but require constant human involvement in the processing process.
Hydraulic and pneumatic modifications are widely used in CNC machines. Here, the movement of the pinole is carried out by the hydraulic cylinder, and the clamping force is regulated by the pressure in the system. This allows you to automate the processing cycle and increase labor productivity. Servo drives Provide high accuracy of positioning of the tool.
Separately, it is worth highlighting heavy money for large diameter machines. They have a reinforced design, often a double pinol to exclude twisting, and additional lubrication systems. The weight of such units can reach several hundred kilograms, so their movement through the stan is carried out through the gearbox from a separate engine or hydraulics.
Adjustment and adjustment of equipment
Quality processing is impossible without the correct configuration of the node. The first step is always to check the balance. To do this, between the cartridge and pin pin pin is clamped control mandrel, and the beat is checked by the indicator at several points. The permissible values of the beat are indicated in the machine passport and usually do not exceed several hundredths of a millimeter.
Adjustment of gaps in the guides is carried out by special wedge slats or adjusting screws. If the pinol has a backlash, you need to tighten these elements. However, overdrawing is also harmful, as it leads to overheating and bullying of rubbing surfaces. Gap. It should be minimal but ensure smooth movement.
☑️ Checklist checklist for cash
When setting the swivel babush for sharpening cones, the following formula for calculating the displacement is used: $S = L \times \tan(\alpha)$, where $L$ is the length of the part, $\alpha$ is the angle of the cone. The shift is made by the screw located at the base of the node. After installation, it is necessary to re-check the reliability of fixing all clamping elements.
Maintenance and lubrication
Regular maintenance extends the life of the equipment and maintains its accuracy characteristics. The main attention should be paid to the purity of the guides and the grandmother herself. Metal shavings, getting between rubbing surfaces, works as an abrasive and quickly disables the knot.
The lubrication system can be manual (through oils) or automatic (spraying or under pressure). In the first case, the operator must regularly check the oil level and the presence of lubricant on the working surfaces. In the second - to monitor the serviceability of the pump and the cleanliness of the filters. Lubricant reduces friction and removes heat from rubbing vapors.
| Element | Type of lubricant | Frequency | Critical signs |
|---|---|---|---|
| Guidelines | Industrial oil (I-20A, I-40A) | Every shift. | Dry, creaking, bullying. |
| Flywheel screw pair | Plastic lubrication (Litol-24) | Once a month | Tight, back lift. |
| Morse cone | Pure engine oil | Before installation | Beating the instrument |
| Hydrocylinder (if any) | Hydraulic oil | Level in the tank. | Slips, moves. |
Particular attention should be paid to the cone hole of pinoli. Even microscopic shavings or dust caught on the cone will cause the tool to be mounted with a beating. Rubbing the cone should be done with a clean rag before each installation of the tool. Special brushes can be used to clean hard-to-reach places.
Typical malfunctions and methods of their elimination
During operation, various problems may arise that affect the quality of work. One of the most common faults is the spontaneous twisting of pinoli. This occurs when the veneer connection is worn or the fixing screws are weakened. The defect is eliminated by replacing the veneer or lifting the fastener.
Another common problem is jamming the movement mechanism. The reason may be the ingress of large shavings, lack of lubrication or deformation of the screw pair. In this case, it is necessary to disassemble the unit, clean it from contamination and defective parts. Repairs A screw pair often requires the replacement of the entire node or professional duct.
⚠️ Attention: It is strictly forbidden to make excessive efforts to the flywheel if the pinol is jammed. This can lead to breakage of the gear teeth or failure of the screw thread.
If there is a cone of the processed parts when using the centers, then the correlation of the grandmother and the spindle is violated. Repeated adjustment of the node is required using the indicator and control mandrel. In some cases, it may be necessary to scald the guide plates of the grandmother to restore geometry.
How to properly knock the tool out of the cone?
To extract the tool from the Morse cone, you cannot knock it out directly with a metal hammer. It is necessary to use a special knockout bar, which is inserted into the slot of the end of the pinoli. With light strokes on the bar, the tool is released. If the tool is stuck, you can carefully warm up the pinoli body, but not the tool itself.
Wear of the inner surface of the pinoli leads to the appearance of a radial beat. Restoration of this unit is possible only in specialized workshops by grinding and grinding for repair size or spraying metal with subsequent processing. At home, it is almost impossible to restore geometry.
Safety technique when working with the node
Working on a lathe is classified as high-risk work, and the back grandmother is no exception. When installing heavy parts between centers, lifting mechanisms must be used. Incorrect installation of the workpiece can lead to its departure when rotating with catastrophic consequences.
Before turning on the machine, always check the reliability of fixing the grandmother on the wall. If the clamping mechanism is weakened, vibration during operation can displace the knot, which will lead to a breakage of the tool or an accident. Security The operator depends on care and compliance with the regulations.
⚠️ Attention: Never leave the key in the cartridge or on the pinoli flywheel after adjustment is complete. The rotating parts can throw away the key with great force.
When drilling holes at high revs, a long shaving is formed, which can wind on the tool. It is necessary to use a hook to remove the chips only after the spindle stops completely. Work in mittens in the presence of rotating parts is strictly prohibited.
Useful tip: To increase the service life of the center in the back grandmother, use a lubricant with the addition of graphite or molybdenum disulfide. This will reduce friction at the point of contact of the center and the workpiece, preventing the metal from jacking and overheating.
Regular check of all elements of the backbone is the key to the stable operation of the entire lathe. Timely detection of backlashes, wear and lubrication disorders allows you to avoid expensive repairs and downtime of production. A qualified operator always keeps this unit in perfect cleanliness and readiness for work.
Main conclusion: The back grandmother is not just a support, but a high-precision unit that requires regular alignment and lubrication to ensure the quality of processing and operator safety.
Frequently Asked Questions (FAQ)
How to check the balance of the back of the grandmother without special equipment?
At home, you can use the method of "two centers". Press the same center mandrels or just centers in the cartridge and pinoli. Bring them to the touch. If the axes match, the ends of the centers will coincide throughout the circle. If there is a bias, you will see a gap on one side. However, this method gives only an approximate result, an accurate check is carried out with an indicator.
Why does the pinole warm up when working?
Heat is usually caused by friction. The main reasons: too tight clamping of wedges of guides, lack of lubrication, pulled tail of the screw or damage to bearings. It is necessary to stop the machine, let it cool, check the level of lubrication and gaps in the guides.
Can I use a back granny to cut a thread with a tag?
Yes, it's a common practice. The tag is clamped in the cartridge, which is installed in the pinol. The rotation of the gauge is transmitted through the rotation of the spindle of the machine (the workpiece is stationary in the recesses or vice versa, depending on the circuit). It is important to ensure the free exit of shavings and the use of LEDs.
What to do if the Morse cone is “licked”?
If the surfaces of the cone are damaged (bobbers, dents), the tool will sit loose or jam it. Small damage can be tried to eliminate laundry with abrasive paste. Deep damage requires grinding the cone on a special machine or replacing the pinoli.
What is the maximum processing length with backbone support?
The maximum length depends on the distance between the centers of a particular machine (RMC). For the machine 16K20 is 1000, 1400 mm and more. However, for very long details, additional support may be required, as the long shaft’s own stiffness may not be sufficient even with two centers.