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About reaming, what is reaming, why this process is done. When and for what?

What is Reaming?

Reaming is the process of enlarging an already made hole to its proper size.
Reaming can finish any hole to a precision of -0.005 mm or up to +0.005 mm. Metals from 0.02 mm to 0.15 mm are cut by the reamer used in the reaming process. It is also called reaming allowance.

drill size for reaming

For reaming by hand reamer or machine reamer, the size of the drilled hole should be smaller than the size of the reamer. Apart from this, it is also necessary to have enough metal before finishing by reamer, because due to less metal finishing will not be achieved as required and more metal will put pressure on the reamer, which will damage the reamer.

(a.)Calculation of drill size

To prepare a hole of a given reamer size, the following formula is used to calculate the size of the drill.

drill size = reamer size – (undersize of reamer + oversize of drill)

(b.)finish size

The diameter of the reamer is called the finish size.

More Information:- type of reamer


After drilling a hole, we always get some big size hole, it is called oversize. The size of the hole is 0.05 mm larger than the size of the drill.


The appropriate drill size is selected to obtain a reamer hole of a particular size. This size remains slightly less than the smaller size of the reamer. It is called undersize.
For lighter metals, the undersize is enlarged by 50%.

Example 1. A hole made in mild steel is reamed with a reamer of 20 mm. Find the drill size to make this hole.
Reamer Size = 20mm
Undersize (as per list) = 0.3 mm
Drill Size = Reamer Size – (Undersize + Oversize)
= 20 – (0.3 + 0.05)
Drill size = 19.65 mm

method of reaming

The type of reaming is chosen based on the equipment available in the workshop or the requirement of finishing. If less diameter and deeper reaming is to be done, then fluted machine reamer is used, but if a lot of finishing is required, then hand reamer is used. For reaming, the size of the hole is kept a little less. The metal required for finishing by the reamer should remain in the hole.

(a.) reaming by hand

  1. First, hold the jab in the vice or fixture.
  2. After that check the size of the hole. That it should not be more than 3% smaller than the size of the reamer.
  3. After this, check the vertical position of the reamer by placing it in the hole. The reamer and holes should be centered.
  4. Move the reamer clockwise with light pressure.
  5. Keep adding proper lubrication to the hole as you move the reamer.
  6. After the reaming process is completed, take out the reamer by rotating it in a clockwise direction.
  7. After this clean the job and reamer and keep it in the proper place.

(b.)reaming by machine

  1. First of all, clamp the job properly on the machine bed or fixture.
  2. Fit the appropriate size reamer in the spindle of the machine.
  3. Apply Mobil oil to the hole and to the spindle before reaming. And slowly bring the handle down very carefully.
  4. Keep the reaming speed too low compared to drilling, this will prevent the reamer from heating up as quickly.
  5. After the work is completed, take out the reamer while walking and clean it and place it at the appropriate place. keep Give.
  6. A pilot reamer should be used for mass production.

Precautions while reaming

  1. Damaged reamer should not be used while reaming. Using this the hole will be undersized.
  2. The reamer should be checked thoroughly before reaming.
  3. Do not put excessive pressure on the reamer while rotating it.
  4. The reamer must be moved carefully and slowly into the drilled hole.
  5. Lubricants must be used while doing the operation.
  6. Metal shavings formed in the operation should be removed from time to time.
  7. The axis of the reamer and the axis of the hole should be in the same line.
  8. The reamer should never be run anti-clockwise.
  9. After grinding the reamer, finishing should be done on oil stone.

More Information:- type of reamer

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