Writing 1:

Dear Supervisor,

I bought four kinds of bearings from ABC Mechanical Store in Hanoi on September 20, 2025, because our stock was empty.

The first is ball bearings, which consist of steel balls, inner and outer rings, and a cage. They reduce friction and are used in motors and fans.

The second is roller bearings, including rollers, rings, and a cage. They can carry heavy radial loads and are applied in conveyors and gearboxes.

The third is tapered roller bearings, made of tapered rollers and rings. Their function is to handle both radial and axial loads, commonly used in car wheels and truck axles.

The fourth is needle bearings, consisting of thin rollers and rings. They are designed for compact spaces and are applied in small gearboxes and pumps.

These bearings will support smooth and reliable machine operation.

Sincerely,
Huy Thien

CAD (Computer-Aided Design) is a technology that uses computers and software to create, modify, and optimize drawings, while manual drafting is the traditional method of drawing by hand with pencils, rulers, and compasses. In the past, designers used to rely on manual drafting, which was slower and less accurate. CAD is used for producing precise and complex designs more quickly. It has the capability of creating both 2D and 3D models, something manual drafting cannot do. People who work with CAD are used to using digital tools and commands. Compared with manual drafting, CAD is more efficient, flexible, and easier to edit. Although CAD software is more expensive and requires computer skills, it saves time and improves accuracy, making it more suitable for modern design work.

Dear Supervisor,

I have purchased four kinds of couplings because our stock was out. I bought them from ABC Mechanical Supplies in Hanoi on September 21, 2025.

The first type is rigid couplings, which consist of two sleeves and bolts. Their function is to connect two shafts firmly without flexibility. They are applied in alignment-accurate machines.

The second type is flexible couplings, made of hubs, a flexible element, and bolts. They allow slight misalignment and are used in pumps and compressors.

The third type is beam couplings, which are made from a single piece of metal with spiral cuts. Their function is to compensate for angular misalignment and provide torsional flexibility. They are commonly used in servo motors and precision equipment.

The fourth type is sleeve-style couplings, consisting of a hollow sleeve and two shaft ends. They are simple, low-cost, and used in light-duty applications such as small conveyors and agricultural machines.

Sincerely,
Huy Thien

AutoCAD is one of the most popular CAD programs developed by Autodesk. It is a powerful software used for creating 2D and 3D designs in engineering, architecture, and construction. Its main features include precise drawing tools, layer management, and compatibility with many file formats. AutoCAD has the capability of producing detailed technical drawings and 3D models. It is used for designing buildings, mechanical parts, and electrical systems. One major advantage of AutoCAD is its accuracy and efficiency, which help save time and reduce errors. Moreover, it allows users to modify and share drawings easily. However, AutoCAD is quite expensive and requires strong computer skills to operate effectively. Despite these disadvantages, it remains one of the most reliable CAD tools in modern design and engineering.

Plastic is a versatile and lightweight material made from polymers. It can be moulded into many complex shapes and is used to produce bottles, containers, ropes, and even parts of airplanes. The main properties of plastic are its strength, stiffness, transparency, and resistance to heat and chemicals. Plastic can withstand high temperatures and does not easily react with other substances. Its advantages include durability, flexibility, and low production cost. However, plastic also has disadvantages because most types are not biodegradable and can cause serious environmental pollution. In the future, it will be possible to develop more recyclable and biodegradable plastics. Scientists will certainly create new bioplastics that bacteria can break down easily, reducing waste and protecting our planet.

There are seven main types of plastic used in daily life and industry. They include PET (1), HDPE (2), PVC (3), LDPE (4), PP (5), PS (6), and ABS (7). PET is lightweight, transparent, and used for beverage bottles. HDPE is strong and recyclable, used for containers and pipes. PVC is durable but should not contact food; it is used for cables and pipes. LDPE is flexible and used for plastic bags. PP is tough and can withstand high temperatures, so it is used in food packaging and car parts. PS is used for disposable cups and boxes. ABS is sturdy and used in electronics and medical equipment. Each type of plastic has different properties and applications, helping engineers choose the right material for specific mechanical purposes.

The milling machine needs regular maintenance to work properly and safely. There are five types of maintenance work you should do. First, clean the guideways every day to avoid interruptions and help control the motion of fluids. Second, check the oil level daily to make sure the engine works efficiently and does not overheat. Third, renew the oil twice a year to keep the machine operating smoothly. Fourth, clean the whole machine every week to remove dust and dirt that can cause problems. Finally, inspect the bearings once a year to prevent slippage and damage. If you follow this plan carefully, your milling machine will run well, stay in good condition, and have a longer life.