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Reaming

What is reaming?

Reaming is a highly precise machining method designed to finish holes to extremely high quality using a multi-blade tool. This process is essential for machinists, machine shops, and manufacturing facilities that work on parts where hole dimensions and surface quality are critical. Reaming offers an excellent surface finish and extremely tight tolerances at high feed rates and shallow cutting depths. It's widely used in demanding applications where the exact size of the holes is crucial for the function and quality of the final product.

Fundamentals of Reaming

The service life of reamers and the success of reaming are influenced by the following factors:

  • Cutting depth: Optimal cutting depth ensures a long reamer life and optimal results. Too much depth can shorten tool life, while too little can cause the reamer to wear out faster.
  • Cutting speed and feed: The performance and durability of the reamer can be improved by carefully selecting the cutting speed and feed rate.
  • Material to be machined: The properties of the work material affect the choice and settings of the reamer. Different materials require different tool parameters and geometries.
  • Runout: Excessive runout can negatively impact accuracy and cause uneven wear on the reamer blades.
  • Centering accuracy: Accurate centering reduces errors and ensures consistent results.
  • Cutting fluid pressure and concentration: Sufficient and properly directed cutting fluid pressure improves machining performance and increases tool life.
  • Chatter: This is especially important when machining small or intersecting holes.
  • Workpiece clamping: Secure clamping is necessary to achieve precise results and prevent vibrations.
  • Blade geometry and quality: The geometry and quality of the reamer’s blades directly impact the machining quality and efficiency.
  • Reamer length and holder: The length of the reamer and quality of the holder affect tool rigidity and accuracy. Shorter lengths and a high-quality holder reduce vibrations and improve machining results.

General Guidelines for Reaming

For the best reaming results, take the following points into account:

  • Allowance: It's important to leave enough material in the hole for reaming, but not too much. Typically, 0.1–0.5 mm is a suitable allowance. Too small an allowance accelerates reamer wear, while too large an allowance may lead to imprecise results.
  • Reamer type and parameters: Select the right type of reamer and proper cutting speed and feed for each job. Ensure the diameter of the pre-drilled hole is correct.
  • Workpiece clamping and machine play: Ensure the workpiece is securely clamped and the machine spindle is free of play. A quality chuck prevents the reamer shank from slipping.
  • Use of cutting fluid: Use cutting fluid as recommended and make sure it reaches the cutting edges. An emulsion is generally recommended for reaming. When machining gray cast iron dry, chip evacuation can be improved with compressed air.
  • Reamer flutes: Keep the reamer flutes clean. Clogged flutes can lead to machining errors and rapid reamer wear.
  • Sharpening: Maintain reamer blades regularly. Accurate sharpening is important for hole quality and tool longevity. Only the cutting and lead cones should be sharpened, not the lands.

Allowance, Clamping, and Cutting Fluid in Reaming

The recommended allowance in reaming depends on the material to be machined and the surface roughness of the pre-drilled hole. Generally, the allowance is about 0.1–0.5 mm. Make sure the workpiece is properly clamped to achieve accurate and efficient machining. When clamping thin-walled workpieces, even clamping forces are especially important. The use of cutting fluid is critical in reaming—the fluid must reach the cutting edge directly, which increases tool life and improves chip evacuation. For solid carbide reamers, the fluid jet is direction-dependent: use an axial flow for straight flute types and a lateral flow for spiral fluted types. Emulsions tend to extend tool life better than oil, and a recommended fluid pressure is 15 bar.

Special Reaming Situations

Reaming can face special challenges when dealing with intersecting holes or inclined surfaces. When machining intersecting holes, the reamer diameter should be less than 22 mm if the intersecting holes are under 2 mm in diameter. When reaming inclined surfaces, the maximum recommended entrance angle is 5°. Additional instructions can be obtained from an expert if needed. The alignment deviation between the pilot hole and the reamer should be as small as possible to minimize vibration and increase accuracy. The pilot hole diameter should allow for the recommended radial cutting depths, and its straightness tolerance should be less than 0.05 mm.

Summary

Reaming is a finishing machining method that demands precision and provides high-quality, accurate holes for machinists, machine shops, and manufacturing facilities. Successful reaming is built on sufficient allowance, accurate tool parameters, secure workpiece clamping, and correct use of cutting fluid. Following these principles ensures excellent surface finish, tight dimensional tolerances, and long service life for cutting tools. Reaming is a critical process that significantly impacts the quality and functionality of end products in various machining tasks.