Calculate finished reamer size, pre-ream hole diameter, machining allowance and material removal for precision hole finishing.
Enter a finished hole size and reaming allowance.
What does a reamer do? A reamer removes a controlled amount of material from an existing hole to improve its dimensional accuracy, roundness and surface finish.
How do I calculate the pre-ream hole size? Subtract the total diametral reaming allowance from the desired finished hole diameter.
Is reaming allowance diametral or radial? Unless otherwise specified, this calculator treats the entered allowance as diametral stock. Half of that value is the radial stock removed from each side.
Can a reamer enlarge a very small hole? Reamers are finishing tools and should generally not be treated as heavy stock-removal tools. The hole should be appropriately prepared before reaming.
Does material affect reaming allowance? Yes. Material hardness, ductility, work hardening, hole size and the type of reamer can influence the appropriate allowance.
Does the drill diameter equal the required pre-ream size? Not necessarily. Drilled holes can vary in size, straightness and location. The actual hole condition should be considered before reaming.
Can I use this for CNC machining? Yes, as a planning calculation. Final tooling parameters should follow the reamer manufacturer's recommendations and the required hole tolerance.
Can this calculate inch reamer sizes? Yes. Enter the desired finished diameter in inches and select the appropriate allowance.
What happens if the allowance is too large? Excessive stock can increase cutting forces, heat and tool wear and may produce a poor surface finish or inaccurate hole.