PR 5602 CNC unit2.pptx.

1. UNIT II STRUCTURE OF CNC MACHINE 9 CNC
Machine Building, Structural Details, Configuration
And Design, Guide Ways – Friction, Anti Friction And
Other Types Of Guide Ways, Elements Used To
Convert The Rotary Motion To A Linear Motion –
Screw And Nut, Recirculating Ball Screw, Planetary
Roller Screw, Recirculating Roller Screw, Rack And
Pinion, Spindle Assembly, Torque Transmission
Elements – Gears, Timing Belts, Flexible Couplings,
Bearings- Maintenance Of CNC Machines.

4. • What are guide ways in CNC?
• The main function of guideways is to make
sure that the cutting tool or machine tool
operative elements moves along
predetermined path. Coefficient of friction for
a LMG is only 1/50th and clearance free as
compared to a traditional slide.

10. What are the different types of guideways in CNC?
Three basic types of guide ways can support linear motion
between machine tool components: rolling-element, hydrostatic
and plain sliding ways.

11. • Guide ways are crucial components in various mechanical systems,
providing support and guidance for moving parts. Here's a comparison of
friction, anti-friction, and other types of guide ways:
• Friction Guide Ways:
– Principle: Friction guide ways typically involve surfaces in direct contact,
where the motion is guided by the friction between the moving and stationary
parts.
– Material: Often made of materials like steel, cast iron, or bronze.
– Advantages:
• Simple design and construction.
• Lower initial cost compared to anti-friction guide ways.
– Disadvantages:
• Higher friction leads to increased wear and tear.
• Limited precision and speed due to frictional resistance.
– Applications: Commonly found in low-precision and low-speed applications
where cost is a significant consideration, such as in woodworking machinery.

16. • Anti-friction Guide Ways:
• Principle: Anti-friction guide ways utilize rolling elements
(e.g., balls or rollers) to reduce friction between the
moving and stationary parts.
• Types: Include linear ball bearings, roller bearings, and
needle bearings.
• Advantages:
– Lower friction results in smoother motion and reduced wear.
– Higher precision and speed compared to friction guide ways.
• Disadvantages:
– Typically higher initial cost due to the complexity of the design
and the need for precision manufacturing.
– Require periodic maintenance such as lubrication.
• Applications: Widely used in high-precision machinery
such as CNC machines, robotics, and linear motion systems
where accuracy and smooth motion are essential.

22. • Other Types of Guide Ways:
• Hydrostatic Guide Ways: Use a thin film of fluid (such as oil) to provide
lubrication and support, reducing friction and wear.
– Advantages: Extremely low friction, high precision, and vibration damping.
– Disadvantages: Complex design, high initial cost, and requires a constant
supply of lubricant.
• Magnetic Guide Ways: Utilize magnetic fields to levitate and guide moving
parts, eliminating physical contact and friction.
– Advantages: Extremely low friction, minimal wear, and high precision.
– Disadvantages: Requires sophisticated control systems, limited load capacity,
and susceptibility to external magnetic fields.
• Air Bearing Guide Ways: Use compressed air to create a thin film of air
between moving and stationary parts, minimizing friction.
– Advantages: Extremely low friction, high precision, and vibration damping.
– Disadvantages: Requires a constant supply of compressed air, limited load
capacity, and sensitivity to contamination.

23. • Let's compare friction guide ways, anti-friction guide ways, and other types of guide ways across various factors:
• Friction:
– Friction Guide Ways: Relatively higher friction due to direct contact between moving and stationary parts.
– Anti-friction Guide Ways: Lower friction due to rolling elements (balls or rollers) reducing contact and friction.
– Other Types of Guide Ways: Offer extremely low friction, especially in magnetic and air bearing guide ways where physical contact is eliminated.
• Wear and Tear:
– Friction Guide Ways: Experience higher wear and tear due to friction between surfaces.
– Anti-friction Guide Ways: Experience reduced wear and tear due to rolling instead of sliding motion.
– Other Types of Guide Ways: Offer minimal wear and tear, especially in magnetic and air bearing guide ways where physical contact is eliminated.
• Precision:
– Friction Guide Ways: Limited precision due to higher friction and potential for play between surfaces.
– Anti-friction Guide Ways: Higher precision due to smoother motion and reduced friction.
– Other Types of Guide Ways: Offer extremely high precision, especially in hydrostatic, magnetic, and air bearing guide ways, where friction is minimal.
• Speed:
– Friction Guide Ways: Limited speed due to frictional resistance.
– Anti-friction Guide Ways: Higher achievable speeds due to reduced friction.
– Other Types of Guide Ways: Can accommodate very high speeds, especially in air bearing and magnetic guide ways, where friction is almost
nonexistent.
• Load Capacity:
– Friction Guide Ways: Limited load capacity compared to anti-friction and other types of guide ways.
– Anti-friction Guide Ways: Generally higher load capacity due to the distribution of load over rolling elements.
– Other Types of Guide Ways: Offer high load capacity, especially in hydrostatic and magnetic guide ways, where load is supported by fluid or magnetic
forces.
• Cost:
– Friction Guide Ways: Lower initial cost due to simpler design and construction.
– Anti-friction Guide Ways: Higher initial cost due to the complexity of design and precision manufacturing of rolling elements.
– Other Types of Guide Ways: Generally higher initial cost due to sophisticated designs and specialized materials or systems.
• Maintenance:
– Friction Guide Ways: Require regular maintenance to manage wear and lubrication.
– Anti-friction Guide Ways: Require periodic maintenance such as lubrication, but less frequently than friction guide ways.
– Other Types of Guide Ways: Maintenance requirements vary; for example, magnetic and air bearing guide ways may require less maintenance but may
need specialized expertise.
• Applications:
– Friction Guide Ways: Found in low-precision and low-speed applications where cost is a significant factor.
– Anti-friction Guide Ways: Commonly used in high-precision machinery such as CNC machines, where smooth motion and accuracy are critical.
– Other Types of Guide Ways: Utilized in applications requiring extremely high precision, speed, or load capacity, such as semiconductor manufacturing
equipment or precision metrology devices.

24. Rotary motion into linear Motion

25. What is the screw motion mechanism?
A screw is a mechanism that converts rotational
motion to linear motion, and a torque (rotational
force) to a linear force.
It is one of the six classical simple machines. The
most common form consists of a cylindrical shaft
with helical grooves or ridges called threads
around the outside.

26. • The Ball Screw is a high-efficiency
method of converting rotary motion
to linear motion by using a
recirculating ball mechanism
between the screw shaft and the nut.
Compared with a conventional sliding
screw, the ball screw requires driving
torque of one-third or less, making it
ideal for saving drive motor power.

27. •
Let's compare the elements used to convert
rotary motion to linear motion:
• Screw and Nut:
– Operation: Basic threaded screw rotates within a nut,
causing linear motion along the axis of the screw.
– Advantages:
• Simple design.
• Cost-effective.
• Suitable for low to medium precision applications.
– Disadvantages:
• Limited load-bearing capacity.
• Higher friction compared to other methods.
• Lower efficiency.

28. • Recirculating Ball Screw:
• Operation: Ball bearings recirculate within the
nut, reducing friction and enabling smoother
linear motion.
• Advantages:
– Higher efficiency due to reduced friction.
– Greater precision.
– Moderate to high load-bearing capacity.
• Disadvantages:
– More complex design compared to basic screw and
nut.
– Higher cost.

29. • Planetary Roller Screw:
• Operation: Multiple threaded rollers transmit
motion between the screw and nut, providing
high load capacity and efficiency.
• Advantages:
– Extremely high load-bearing capacity.
– High efficiency.
– Suitable for heavy-duty applications.
• Disadvantages:
– More complex and expensive than ball screws.
– Requires precise manufacturing.

30. • Recirculating Roller Screw:
• Operation: Similar to ball screws, but uses rollers
instead of balls for improved load-bearing
capacity and durability.
• Advantages:
– Higher load capacity compared to ball screws.
– Enhanced durability.
– Good for applications with high shock or vibration.
• Disadvantages:
– More expensive than ball screws.
– Complex design.

31. • Rack and Pinion:
• Operation: Gear (pinion) meshes with linear
toothed rack, translating rotational motion into
linear motion.
• Advantages:
– Simple and cost-effective.
– Suitable for applications requiring high speed and
moderate precision.
– Commonly used in automotive steering systems.
• Disadvantages:
– Lower precision compared to screw-based systems.
– Limited load-bearing capacity.
– Prone to wear and backlash.

32. • Comparison:
• Load Capacity: Planetary roller screws have the highest load
capacity, followed by recirculating roller screws, recirculating ball
screws, screws and nuts, and finally rack and pinion.
• Precision: Recirculating ball screws and planetary roller screws
offer the highest precision, followed by recirculating roller screws,
screws and nuts, and rack and pinion.
• Cost: Screws and nuts are the most cost-effective, followed by rack
and pinion, recirculating ball screws, recirculating roller screws, and
planetary roller screws.
• Complexity: Rack and pinion and screws and nuts are the simplest
in terms of design and implementation, followed by recirculating
ball screws, recirculating roller screws, and planetary roller screws.
• Applications: The choice depends on the specific requirements of
the application, such as load capacity, precision, speed, and budget.

33. Elements of power transmission
• Machine elements used for transmitting the
power :- Machine. elements like gears, shafts,
clutches and brakes, pulleys, belts, chain,
sprocket, are used to transmit power from
one place to another. Machine elements used
for support of other components

42. Which bearing is used in CNC
machine?

44. Angular contact bearing
In angular contact ball bearings the line of
action of the load, at the contacts between
balls and raceways, forms an angle with the
bearings axis. The inner and outer rings are
offset to each other and the bearings are
particularly suitable for carrying combined
radial and axial loads.

45. Deep groove ball bearing
The 'groove' is the depth of the raceway into
which the balls fit. Deep groove single row ball
bearings are also known as Conrad bearings.
Deep groove ball bearings can carry higher
radial and axial loads than their shallow groove
ball bearing counterparts.