Reaming is a finishing operation used to bring a drilled or bored hole to its final, precise diameter. The reamer removes a small amount of material – the *reaming allowance* – which must be left in the pre‑hole to avoid excessive tool wear and to achieve the desired surface finish.
The allowance is calculated as the difference between the desired final diameter and the diameter of the hole that is produced by the preceding operation (usually drilling). Providing the correct allowance ensures the reamer cuts efficiently, reduces the risk of chatter, and maintains dimensional accuracy throughout production runs.
Typical allowances range from 0.02 mm to 0.10 mm (0.001–0.004 in) for steel, and may be larger for softer materials. Selecting an appropriate allowance depends on material hardness, reamer geometry, and the required tolerance class.
What is reaming allowance?
How do I calculate reaming allowance?
Why is reaming allowance important?
What factors affect reaming allowance?
Can reaming allowance be too small or too large?
Is there a standard reaming allowance for all materials?
How does reaming differ from drilling?
Results are for informational purposes only and do not constitute professional advice.