Introduction
Drills and reamers can all be used for creating holes, while they play different roles in CNC machining. Drills can remove materials efficiently to form a new hole, and reamers will fine-tune the hole to enable its higher accuracy and smoother surfaces. From industrial construction to CNC machining, understanding the differences between drilling and reaming is beneficial for machining professionals to make the decision between efficiency and precision.
Overview of Drills and Reamers
When hole-making operations are needed in CNC machining, drill bits are often considered first. Drill bits feature fewer cutting edges to remove materials efficiently. However, after drilling, some holes will have rough edges or be of improper sizes. To solve this, reamers can be used to improve the existing holes. Reamers are precision rotary cutting tools used for removing a minimal amount of chips to achieve excellent dimensional accuracy and roundness.
Drill vs Reamer: Key Differences
Primary Functions
In hole-making operations, drilling is the first step, which can be considered as rough construction. Drill bits are typically applied to drilling initial holes by removing a large amount of material efficiently. In this comparison, we focus on talking about standard twist drills used before reaming.
After drilling, reaming is used for refining and finishing an existing hole to improve its surface finishes and tight tolerances. Reamers have the typical types with versatile functions.
- High-Speed Steel Reamers
Extensively applied to most materials.
- Carbide Reamers
Suitable for machining harder materials.
- Hand Reamers
Designed for manual finishing,
- Machine Reamers
Combined with CNC machines to achieve mass production.
- Spiral Flute Reamers
Achieve improved chip evacuation, especially in reaming blind holes.
- Adjustable Reamers
Provide flexible sizes for convenient repair and maintenance.
Typically, reamers are engineered to enlarge the pre-drilled hole, which has a slightly smaller size than the final diameter, with enhanced dimensional accuracy, which enables the perfect fit for precise components and perfect hole alignment in complex assemblies. Reamers can also improve internal surface finishes by removing minor imperfections left after drilling, which significantly decreases the friction between the shafts and holes. Moreover, they are ideal for removing burrs to eliminate the minor inaccuracies from the initial drilling, such as the roundness deviation or insufficient straightness.
Visual Comparison
Drilled holes and reamed holes are significantly different when we inspect their surface qualities with our eyes.
On one hand, the drilled holes typically feature visible spiral tool marks, slightly oval shapes, and rough hole surfaces. Besides, the hole diameters can be inconsistent and lacking in hole alignment. On the other hand, reamed holes are commonly equipped with smooth surfaces, even without tool marks and burr formation. They have the standard circular shape and polished surfaces. The hole diameters are uniform throughout the depths.
In practical applications, the visual comparison can be considered as improved properties, extended service life, and reliable performance in complex assemblies that require tight tolerances.
Geometry Design
Drill bits are commonly designed with 118° or 135° pointed tips. They are designed with deep flutes to promote their chip evacuation. Moreover, their two sharp cutting edges can efficiently remove a large amount of material for initial holes.
Reamers are engineered with shallow straight or spiral flutes and minimal point angles. Unlike drill bits, the eaming allowance of reamers is often between 0.002″ and 0.015″ of the material. Machine reamers and hand reamers feature multiple cutting edges to evenly distribute cutting forces to improve the smooth surfaces of holes.
Finish Quality
Compared with reamers, drill bits will typically create rougher surfaces. Upon visual inspection, we will find out the tool marks and micro-tears of drilled holes, which will affect the final properties of practical applications. Although drilled holes can satisfy most of the drilling requirements, further finishing is necessary for the ultimate precision assemblies.
Reamers can achieve minimal surface roughness with removed material ranging from 0.02 to 0.2 mm. Their multiple cutting edges enable their superior capabilities in evenly removing materials around the circumferences of holes. The finish quality of reamed holes can typically achieve 32 to 125 microinches, while drilled holes are 125 to 250 microinches under proper machining conditions. This comparison is crucial for applications where appearances with consistency are the priority.
Tolerance Capabilities
Drills and reamers have significant differences in tolerance capabilities. Drilled holes can generally control the tolerances within ±0.005 inches.
Compared with drill bits, reamed holes can achieve more rigorous tolerances, which can be steadily limited within ±0.0005 inches. Reamed holes can even promote the roundness and shape accuracy of holes, while drilled holes will have slight irregularities. Undoubtedly, reamers are essential for being applied to precision applications like the manufacturing of engine components with rigorous tolerance control and roundness.
Cutting Edge Design
The unique cutting edges are essential for improving machining efficiency and surface qualities in practical applications.
Drill bits are typically designed with sharp cutting edges, including two primary lips and one chisel edge, enabling their efficient penetration of hard materials and higher chip evacuation. The cutting-edge design of drill bits focuses on improved material removal rates, while it will always come with aggressive cutting forces and possible hole deviation.
However, reamers are designed with multiple cutting edges, which are slightly tapered to make it easy to guide reamers into holes. Their cutting edges are precision-ground and equipped with unique lead angles, evenly distributing cutting forces. This kind of cutting-edge design can effectively control the material removal with enhanced roundness and surface finishes. Hence, reamers are the perfect choice for attaining the tight tolerance and superior accuracy in hole-making operations.
Material Removal Efficiency
Drills are ideal for shearing materials away, and reamers are suitable for scraping materials. Drill bits have a superior material removal efficiency than reamers. That’s why reamers are used to improve surface quality.
The amount of material drill bits can remove per minute is far beyond that of reamers. Typically, drilling is the first step, as the material removal rate of drilling can be extended up to approximately 10 times the MRR of reaming.
Whereas, reamers have relatively 30% to 50% more rapid feed rates than drills. Combined with lower spindle speeds, they can ensure high precision and efficiency. They can achieve higher hole accuracy and surface finishes. Moreover, they can achieve unmatched dimensional consistency and hole alignment.
Typical Applications
- Automotive Industry
In the automotive industry, both drills and reamers are widely used for manufacturing engine components and body structures. In machining engine cylinders, drilling should be utilized first for producing a large number of holes in cylinder bores, while reaming can enhance the dimensional accuracy by finishing holes to ensure the precision alignment.
- Aerospace Industry
Tight tolerances of hole accuracy are essential in the aerospace industry, which should be commonly controlled within 0.001 inches. When machining hydraulic devices, drills are typically used for creating pilot holes in aluminum alloys and titanium components. Reamers are applied for finishing holes in aircraft structures and engine parts to improve their roundness and straightness.
- Industrial Manufacturing
In CNC machining and industrial production lines, drill bits often deal with creating pre-holes with high material removal rates. After drilling, reamers are used in finishing holes with improved accuracy and consistency, which is especially crucial in high-volume work.
- DIY Applications
DIY users and hobbyists depend on standard drill bits for most uses due to their high efficiency and convenience. When it comes to finishing operations or repairing work, they will use reamers to improve the hole surfaces in woodworking or metal fabrication.
Reamer vs Drill Bit: How to Choose?
Making a selection between a drill and a reamer depends on the surface finish requirements, tolerance standards, and application scenarios.
- Step 1: Consider Your Machining Requirements
You can choose drills if you require a high material chip removal rate to create holes efficiently, or if you don’t have strict standards of tolerances. When you have demanding requirements of hole accuracy, tight tolerances, and high-quality surfaces, reamers will be the ideal choice.
- Step 2: According to Your Project Scale
In precision applications, you need to use drill bits to create slightly smaller holes, and then use reamers to further finish to the final diameter. In mass production, you’d better combine drilling and reaming to ensure machining consistency and the perfect fit of components.
When to Use Drills vs Reamers?
- Use Drills:
When you need to create a new hole in the solid material, you need to choose a drill. Besides, you only need to do rough work, and the accuracy of the holes isn’t a priority before secondary processing.
- Use Reamers:
You need to use reamers if you want to improve the internal surfaces of pre-holes or when you want tight tolerances of less than 0.001 inches. Moreover, when the holes are undersized, you can use reamers to correct their errors.
Final Thought
Drills are the preferred tools when you need to do the initial drilling, which is engineered to remove materials efficiently. Reamers are typically used for finishing existing holes to improve their dimensional accuracy and smooth surfaces. If you have any demand for drilling and reaming, please contact JINOO. We can provide you with high-quality carbide drills and carbide reamers for CNC machining, which can surely achieve your requirements of efficiency and precision.
FAQ
Can reamers be used to drill a hole from scratch?
No. Reamers are not designed to create holes in solid material. They can only be used for finishing pre-drilled or pre-bored holes by removing a small amount of material to improve their accuracy.
How much material should be left for reaming after drilling?
For reaming harder materials, the reaming allowance should be less than that of soft materials. The size of pre-drilled holes should be 0.005″–0.015″ smaller than the final holes.
Why are drilled holes not perfectly round?
Because of the tool deflection and uneven cutting forces, drilled holes will sometimes be slightly oval-shaped. However, reamers can correct their irregularities by removing extra materials evenly.
Is reaming essential for all holes?
No. Reaming is not essential for all holes, but it can be crucial when you have demanding requirements of tight tolerances and smoother surfaces.
Does reaming need to be done at a higher or lower speed than drilling?
Compared with drilling, reaming requires a lower spindle speed with higher feed rates to minimize the tool chatter and enhance the surface qualities.
Can I ream a hole that is already oversized?
No. Reamers can’t be used for decreasing the hole sizes. If the holes are already oversized, you may need to change into boring or sleeving to improve the situation.
What will happen if I skip drilling and go straight to reaming?
If you skip drilling and go straight to reaming, reamers will be damaged as they are not suitable for creating initial holes with high material removal rates. Hence, it will surely lead to poor results in machining.
Is lubrication necessary in reaming?
Yes. Using lubrication properly is necessary for extending the tool service life and reducing tool friction, especially when reaming steel and stainless steel. Different cutting fluids are required for diverse materials.
What is ideal for creating precision holes: drilling, boring, or reaming?
The ideal machining sequence should be drilling → boring → reaming. Firstly, use drill bits to create holes efficiently, and then utilize boring operations to enhance hole alignment and straightness. Finally, reaming will be used to promote the final hole sizes with improved precision.
What will happen if I keep using dull drill bits or reamers?
Continuing to use dull tools will cause poor hole quality. You’d better inspect your drill bits and reamers regularly and replace tools promptly to avoid excessive tool wear and poor results.
