Things You May Want to Know About Reaming

What is Reaming

Reaming is a cutting process to enlarge the existing hole and create a smooth inner surface. It is done by a multi-edge tool called a reamer. 

Compare to the internal grinding process and fine boring process, Reaming is a cost-effective method to create precise and smooth holes.

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Reamer Types

There are two main types of the reamer, hand reamers and machine, or chucking, reamers. 

  • Hand reamers have a straight shank with a square end to fit a wrench. They have parallel flutes.
  • Machine reamers are used on machine tools such as drill presses, lathes, and screw machines. They have either straight or tapered shanks and spiral flutes. 

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Hand reamer and machine reamer

What is the Surface Roughness of a Reamed Hole?

In general, the average surface roughness Ra for reaming is in the range between 0.8µm and 3.2µm, but it can reach as low as 0.4 µm by high-accuracy reaming.

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What is Recommended Hole Size before Reaming?

Before reaming, The hole should be drilled to an undersized diameter. It varies from different materials. Typically, the rule of thumb is to keep the stock allowance of 0.15 mm to 0.25 mm for the rough reaming process, and 0.05 mm to 0.15 mm for the fine reaming process. 

If an insufficient stock allowance is left for the reamer to cut, the reamer will burnish instead of cutting, which will lead to excessive wear, shorter tool life, and inability to hold diameter tolerances.

If too much stock allowance is left for the reamer to cut. It will increase the cutting pressure and damage the reamer, resulting in the roughness of the cutting surface.

To know more about the pre-ream hole size, you can refer to the pre-ream drill hole size chart.

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How to Choose the Reaming Feeds and Speeds

In general, reaming is done at 1/2~2/3 of the speed and 2~3 times the feed rate as drilling on the same material. 

Take a hole with a 1” diameter on a low carbon steel workpiece for example, to obtain good surface roughness by a carbide-tipped reamer, the feed rate can’t exceed 0.02”/r, while, the speed is range from 70 to 100 SFPM.

Click here to check the speeds and feeds for the kind of carbide-tipped reamer.

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Troubleshooting for Reaming

Oversized holes

  • The reamer diameter is too big.
  • Cutting speed/feed is too high.
  • Runout of spindle or tool is not good.
  • There is a built-up edge.
  • The oil percentage in the coolant is too high.
  • Misalignment between the pre-drilled hole and the reamer.

Tapper holes

  • Runout of spindle or tool is not good.
  • The pre-drilled hole does not align with the reamer.
  • The reamers are not piloted accurately.

Poor surface finish

  • Built-up edge caused by no or Insufficient coolant.
  • Chip removal is not good.
  • Poor surface in the pilot bore.
  • Excessive Spindle Runout.

Damaged tools, such as broken cutting edge

  • Undersized holes
  • Excessive tool wear.
  • Cutting speed/feed is too low.
  • Workpiece with thin-wall.
  • Workpiece springs back after reaming.
  • Too small stock allowance for reaming.

Reamer clamps and breakage

  • The back taper is too small.
  • Too much stock allowance.
  • Cutting chamfer is unequal wear.
  • The feed rate is too high.
  • Poor chips removal.

Chatter marks in the holes

  • Built-up edge.
  • Too low oil percentage in the coolant.
  • Too small stock allowance for reaming.
  • The reamer is clamped wrong in the holder.
  • Spindle run-out is not good.
  • The feed rate is too low.

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Reaming is one of the cutting process, we will share with you more other machining method in the coming blogs. Stay tune.