When drilling holes on parts, a drill bit is usually used for cutting. However, drill bits cannot produce precisely sized holes because their main function is to quickly remove large amounts of material. On the contrary, reamers are used to enlarge existing drilling holes to precise dimensions with strict tolerances. Reamers are designed only for removing small amounts of material, and are rotary precision machining tools with straight or spiral edges, used for expanding or repairing holes. Due to the small cutting amount, their machining accuracy requirements are usually higher than those of drill bits. It can be manually operated or installed on a drilling machine to work.
Reamers can be made of HSS (high-speed steel), carbide, and high alloy steel. Expanding holes is considered a precision machining process
Different Types of Reamers
Different reamers are available, each with its optimal use case. Some of the more common reamer types are listed below:
Shell Reamers:
Shell reamers typically have a hollow cylindrical geometry and straight grooves, and are used on CNC and manual machines. They are particularly effective in single pass enlargement and precision machining of holes, accelerating the machining process. Spiral grooves and twisted grooves were also used. The inner diameter of the reamer is suitable for installation on the spindle. Compared to standard reamers, quick replacement is beneficial for shell reamers because only the blade needs to be replaced, without the need to replace the entire handle. Due to the groove at the back of the reamer, it can prevent rotation during the reaming process, allowing the lug to engage with the spindle.
Hand Reamers:
The hand reamer is designed to be used manually without machine assistance, therefore it is not suitable for CNC machine tools. The rear end of the reamer handle is square, so it can be engaged with a tap wrench or wrench. The front of the reamer is slightly tapered, allowing it to self align in the hole, making it easier to use.
Ring Reamer
This type of reamer typically has multiple cutting bits connected to the periphery of the ring, similar to a face milling cutter. Circular reamers are used at high speeds and are mainly used for larger diameter holes. Limited expansion is a key design feature of most annular reamers, which limits tool wear, improves accuracy, and extends service life.
Chucking Reamer
These reamers are the most commonly used and have a straight or Morse taper shank. The chuck reamer is sometimes also known as a mechanical reamer. The grooves on the chuck reamer can be straight or spiral. These reamers are usually fixed in CNC or manual drilling machines, lathes, milling cutters, or chucks, hence their names. The tip of the reamer usually has a 45 degree chamfer. The chuck reamer is used to increase the size of existing drilling holes, giving them more precise dimensions and stricter tolerances.
Expansion Reamer
The design purpose of the expansion reamer is to increase its diameter by rotating the screw, and then move the cutting edge radially outward. This extension allows for tool wear compensation and fine control of different apertures. The modular design of these reamers is not as hard as standard reamers and can only remove a relatively small amount of material.
Drill Reamer
Drill bit reamer, also known as reamer, allows for drilling and reaming in the same operation, thereby saving time. The reaming drill bit is most suitable for through-hole drilling. It must be noted that if very precise holes are required, it is best to use a separate reaming drilling operation. However, if the accuracy requirements are not too strict, this type of reamer can save costs and simplify the machining process.
How to Ream a Hole
Expanding a hole is a multi-step process, starting from drilling.
The size of the drill bit must be slightly smaller than the required diameter for reaming – in most cases, it should be 2% to 4% smaller.
The standard reaming chart displays the required drill bit size for a specified reamer diameter. Once drilled, the hole can be reamed.
If using a machine for hole expansion, please ensure that the reamer is completely aligned with the hole.
If it is manual reaming, make sure to use a reamer with a tapered leading edge to help align the tool.
If the reamer has spiral grooves, ensure that the direction of rotation of the reamer is correct.
Using a reamer in the opposite direction will make the blade blunt.
Applications of Reamers:
Achieving Precision Tolerances:
Reamers are indispensable when precise hole diameters and tight tolerances are required. They help achieve the desired fit and finish in critical components.
Surface Finish Enhancement:
The cutting action of reamers contributes to a smoother surface finish inside the machined hole. This is crucial in applications where reduced friction or improved aesthetics are paramount.
Hole Alignment and Straightness:
Reamers aid in ensuring the alignment and straightness of drilled holes. This is particularly important in applications where components need to fit together seamlessly.
Batch Production:
In mass production scenarios, machine reamers excel in delivering consistent results. They contribute to the efficiency of the production process and ensure uniformity across a large volume of machined parts.
Challenges and Best Practices:
Proper Speeds and Feeds:
Reamers require specific cutting speeds and feeds to operate effectively. Understanding the material being machined and adhering to recommended speeds and feeds is essential.
Regular Inspection and Maintenance:
Regular inspection and maintenance of reamers are crucial for ensuring optimal performance. Dull or damaged cutting edges can compromise the quality of the machined holes.
Coolant and Lubrication:
The use of appropriate coolant or lubrication is essential during reaming operations. It helps dissipate heat, prolongs tool life, and ensures the quality of the machined surface.
In the intricate dance of machining, reamers take center stage in the pursuit of perfection. Whether in small-scale operations requiring manual precision or large-scale production demanding efficiency, the choice of the right reamer and the implementation of best practices contribute to the impeccable quality of machined components.