What is Reaming: a Precision Machining Operation.
What is reaming? Reaming is a precision machining operation. More specific, we use reaming to enlarge the diameter of an existing hole to a precise dimension and surface finish. It is a critical process in manufacturing, repair, and maintenance of components and machinery. To clarify, this process involves the use of a machining tool called a reamer that removes a small amount of material from the hole surface to achieve the desired dimension and finish. In this article, we will explore the reaming process, its benefits, types of reamers, and the applications in various industries.
Reaming Process
Reaming is a finishing operation that follows drilling or boring. As one of the CNC machining processes, it involves the use of a multi-fluted cutting tool called a reamer that removes a small amount of material from the hole surface to achieve the desired dimension and finish. The reamer has several cutting edges, and each edge removes a small amount of material. The process is repeated until the desired diameter and surface finish are achieved. The reaming process is essential to ensure the hole is round, straight, and has a smooth surface finish. The reaming process can be done by hand or machine. Hand reaming involves using a hand-held reamer to manually enlarge the hole. Machine reaming involves using a reaming machine such as a CNC machine or a drilling machine, that automates the reaming process. The machine reamer is mounted on a spindle that rotates at low speed, and the workpiece is held in a fixture that allows for precise positioning and alignment. The machine reamer is fed into the hole using a feed mechanism, and the process is controlled by the operator.
Benefits of Reaming
Reaming offers several benefits, including:
- Improved hole accuracy: Reaming ensures that the hole is round, straight, and has a precise diameter. This is important in industries such as aerospace, automotive, and medical where accuracy is critical.
- Improved surface finish: Reaming produces a smooth surface finish that reduces friction and wear. This is important in industries such as bearings, valves, and pumps where low friction is essential.
- Increased tool life: Reaming reduces tool wear and extends the life of cutting tools such as drills and end mills. This is because reaming removes only a small amount of material compared to drilling or boring.
- Cost-effective: Reaming is a cost-effective process compared to other machining processes such as grinding or honing. It is also faster and requires less setup time.
Types of Reamers
There are several types of reamers, including:
- Hand reamers: These are manually operated reamers that are used for small jobs and low-volume production. They are suitable for reaming soft materials such as plastics and non-ferrous metals.
- Machine reamers: These are automated reamers that are used for high-volume production. They are suitable for reaming hard materials such as steel and cast iron.
- Taper reamers: These are reamers that have a tapered cutting edge. They are used for reaming tapered holes and are commonly used in the automotive industry for reaming steering components.
- Adjustable reamers: These are reamers that can be adjusted to achieve different hole sizes. They are suitable for low-volume production and repair work.
Comparison table:
| Type | Description | Typical Use |
|---|---|---|
| Hand Reamer | Operated manually with a wrench | Repairs, low-volume work |
| Machine Reamer | Mounted on CNC or drilling machines | Mass production, hard metals |
| Taper Reamer | Tapered cutting edge | Tapered holes in automotive and mechanical parts |
| Adjustable Reamer | Adjustable blades for variable sizes | Custom jobs and maintenance |
Applications of Reaming
Reaming is used in various industries, including:
- Aerospace: Produce precise holes in aircraft components such as engines, landing gears, and fuselage.
- Automotive: The precision machining operation of making holes in engine components such as cylinder blocks, connecting rods, and crankshafts.
- Medical: Creating holes in medical implants such as hip replacements and dental implants.
- Oil and gas: Production of precise holes in oil and gas drilling equipment such as drill bits and casings.
- Manufacturing: Used in various manufacturing industries such as metalworking, woodworking, and plastics to produce precise holes in components.
- Bearings: Reaming is used to produce precise holes in bearings, which are used in various industries such as aerospace, automotive, and heavy machinery.
- Valves: Improve tolerances of holes in valve components such as valve bodies and valve seats. This ensures that the valve operates smoothly and efficiently.
- Pumps: Used to produce precise holes in pump components such as impellers and housings. This ensures that the pump operates with minimal friction and wear.
Reaming and obtaining Tight Tolerances
Reaming achieves tight dimensional tolerances typically in the range of:
- ±0.005 mm to ±0.025 mm (±0.0002″ to ±0.001″)
The final accuracy depends on factors such as:
- The initial hole quality from drilling or boring
- The material type (steel, aluminum, brass, etc.)
- The reamer geometry and number of flutes
- The speed, feed rate, and setup rigidity
A reamer with more flutes produces a finer surface and tighter tolerance, while fewer flutes allow faster material removal.
Tolerance Tables
Tolerance tables provide a standard set of tolerances for different machining operations, including reaming. These tables are based on the size of the hole being reamed, the type of reamer being used, and the material being reamed.
The International Organization for Standardization (ISO) has established a set of standards for tolerances in machining operations, including reaming. These standards provide a common set of tolerances that can be used by manufacturers and suppliers to ensure that components are manufactured to a consistent level of accuracy. The ISO tolerance standards for reaming specify the upper and lower limits of the acceptable range of hole sizes for each reamer size. For example, for a nominal hole size of 10mm, an H7 tolerance (which indicates a hole size range of 10.000mm to 10.012mm) may be specified. It’s important to note that the tolerances specified in the ISO standards are only a guide and may not be appropriate for all applications. The actual tolerance requirements for a specific application may depend on factors such as the intended use of the component, the material being used, and the assembly requirements.
Reaming Tolerances
| Process | ISO Tolerance Grade | Example: 10 mm Hole | Surface Finish |
|---|---|---|---|
| Drilling | H12 – H14 | 10.000 – 10.070 mm | Ra 3.2 – 12.5 µm |
| Boring | H8 – H9 | 10.000 – 10.027 mm | Ra 1.6 – 3.2 µm |
| Standard Reaming | H7 | 10.000 – 10.015 mm | Ra 0.4 – 1.6 µm |
| Precision Reaming | H6 | 10.000 – 10.009 mm | Ra 0.4 – 0.8 µm |
| Internal Grinding | H5 – H6 | 10.000 – 10.006 mm | Ra 0.1 – 0.4 µm |
H7 and H6 Tolerance by Hole Size
| Nominal Size | H7 Range | H6 Range | Drill Before Reaming |
|---|---|---|---|
| 6 mm | 6.000 – 6.012 mm | 6.000 – 6.008 mm | 5.8 mm |
| 8 mm | 8.000 – 8.015 mm | 8.000 – 8.009 mm | 7.8 mm |
| 10 mm | 10.000 – 10.015 mm | 10.000 – 10.009 mm | 9.8 mm |
| 12 mm | 12.000 – 12.018 mm | 12.000 – 12.011 mm | 11.8 mm |
| 16 mm | 16.000 – 16.018 mm | 16.000 – 16.011 mm | 15.8 mm |
| 20 mm | 20.000 – 20.021 mm | 20.000 – 20.013 mm | 19.8 mm |
| 25 mm | 25.000 – 25.021 mm | 25.000 – 25.013 mm | 24.75 mm |
Note: Tolerances per ISO 286. The “Drill Before Reaming” column shows the recommended pre-drilled hole size, leaving 0.1 – 0.25 mm of material for the reamer to remove. Actual results depend on material, reamer condition, machine rigidity, and cutting parameters.
Conclusion Reaming is a critical precision cnc machining process in components manufacturing, repair, and maintenance of components and machinery. It involves the use of a multi-fluted cutting tool called a reamer that removes a small amount of material from the hole surface to achieve the desired dimension and finish. Reaming offers several benefits, including improved hole accuracy, improved surface finish, increased tool life, and cost-effectiveness. There are several types of reamers, including hand reamers, machine reamers, taper reamers, and adjustable reamers. Reaming is used in various industries, including aerospace, automotive, medical, oil and gas, manufacturing, bearings, valves, and pumps.
Reaming Questions
Common questions about the reaming process, reamer tools, and achievable tolerances.
What is reaming in machining?
Reaming is a finishing operation that enlarges an existing drilled or bored hole to a precise diameter and surface finish. A multi-fluted cutting tool called a reamer removes a small amount of material (typically 0.1 to 0.3 mm per side) from the hole wall. The result is a round, straight hole with tight diameter tolerance (H7 or H6) and smooth surface finish (Ra 0.4 to 1.6 µm). Reaming always follows drilling; it cannot create a hole from solid material.
What is the difference between drilling, boring, and reaming?
Drilling creates the initial hole from solid material using a twist drill. The result is rough (Ra 3.2 to 12.5 µm) with loose diameter tolerance (±0.1 mm or worse). Boring enlarges an existing hole using a single-point tool, allowing precise diameter control and correction of positional errors. Reaming is a finishing pass after drilling or boring that achieves the tightest diameter tolerance (H7, H6) and best surface finish (Ra 0.4 to 1.6 µm) with the fastest cycle time. Use drilling for rough holes, boring for large diameter corrections or non-standard sizes, and reaming for final precision on standard hole sizes.
What tolerances can reaming achieve?
Standard machine reaming achieves H7 tolerance (e.g., 10.000 to 10.015 mm for a 10 mm hole). Precision reaming achieves H6 (e.g., 10.000 to 10.009 mm). These are IT7 and IT6 grades per ISO 286. Surface finish is typically Ra 0.4 to 1.6 µm depending on material, cutting speed, and reamer condition. For comparison, a drilled hole is typically H12 to H14 and a bored hole is H8 to H9.
What types of reamers are there?
Hand reamers have a slight taper at the tip for manual alignment and are turned by hand with a tap wrench. Machine reamers (chucking reamers) have a straight shank or Morse taper for use in CNC machines or drill presses. Adjustable reamers allow fine diameter adjustment using expandable blades. Shell reamers fit onto an arbor and are used for large bore sizes. Tapered reamers produce tapered holes for taper pins. Carbide reamers are used for hard materials and high-volume production where tool life is critical.
Can reaming be done on a lathe?
Yes. On a CNC lathe, the reamer is held stationary in the tailstock or turret while the workpiece rotates. This is common for turned parts that need a precise bore, such as bushings, bearings, and connector housings. The workpiece rotation provides the cutting speed while the reamer feeds axially into the hole. The same H7/H6 tolerances are achievable on a lathe as on a milling machine.
What is the difference between reaming and tapping?
Reaming produces a precise smooth bore. Tapping cuts threads inside a hole. They are completely different operations with different tools and different purposes. A reamed hole accepts a press-fit pin, bearing, or shaft. A tapped hole accepts a bolt or screw. Both typically follow drilling: drill first, then ream (for a precision bore) or tap (for a threaded hole). Some parts require both operations on different holes.
How much material does a reamer remove?
A reamer typically removes 0.1 to 0.3 mm on the diameter (0.05 to 0.15 mm per side). The drilled hole should be undersized by this amount. For example, to ream a 10.00 mm H7 hole, drill to 9.8 mm first. Removing too much material overloads the reamer and causes chatter, poor finish, and rapid tool wear. Removing too little can cause the reamer to rub instead of cut, which burnishes the surface but doesn't achieve the correct diameter.
What cutting speed and feed should I use for reaming?
Reaming speeds are typically 50 to 70% of the drilling speed for the same material. For aluminium: 15 to 25 m/min with HSS reamers, up to 60 m/min with carbide. For steel: 8 to 15 m/min with HSS, 20 to 40 m/min with carbide. Feed rate is higher than drilling: 0.1 to 0.5 mm/rev depending on hole diameter and material. Always use cutting fluid to flush chips and improve surface finish. Consult the reamer manufacturer's data sheet for specific recommendations.
When should I use reaming instead of boring or grinding?
Use reaming when you need H7 or H6 tolerance on a standard hole diameter and want the fastest cycle time. Reaming is quicker than boring for standard sizes because it's a single-pass operation with a fixed-diameter tool. Use boring when the hole diameter is non-standard, when you need to correct positional error from drilling, or when the hole is too large for available reamers. Use grinding (internal cylindrical grinding) when you need tighter than H6 tolerance or surface finish below Ra 0.4 µm. See our tolerances guide for more detail.
