Reaming

How to use the reamer allowance calculator

Enter the final hole diameter, select the accuracy grade, workpiece material, reaming type and previous operation - the calculator will automatically calculate the recommended allowance for the diameter and the diameter of the preliminary drilling or boring.

Why allowance is important: A reamer is a finishing tool; it does not correct the position of the hole or remove large metal. Its task is to remove a thin, precisely calibrated layer, forming the final geometry and roughness. Too small an allowance results in friction instead of cutting: the tool “polishes” the surface, does not cut - the hole is outside the tolerance. Too much allowance causes vibration, scuffing and taper.

What influences the choice of allowance

Diameter. With increasing diameter, the absolute allowance increases: for Ø6 mm 0.08–0.18 mm is enough, for Ø50 mm – already 0.18–0.40 mm.

Previous operation: After boring, the surface is more accurate than after drilling - the allowance can be reduced by 15–20%. After the rough scan - even less.

Material. Stainless steels (group M) and heat-resistant alloys (group S) are prone to work hardening and sticking - they require less allowance and sharp geometry. Cast iron (group K) cuts cleaner - it allows a slightly larger allowance.

Reamer type. Carbide reamers work with a smaller allowance than HSS - higher rigidity, less elastic force. Adjustable sweeps allow for a slightly larger range.

Hole depth. When L/D > 5, the risk of axis deviation, runout and insufficient coolant supply increases - it is recommended to reduce the allowance and use a guide bushing.

Frequently Asked Questions

Is the allowance per side or per diameter? In this calculator – per diameter (the difference between the diameter of the preliminary hole and the final diameter of the reamer).

Is it possible to ream a hole after drilling without boring? Yes, if the drill runout does not exceed 0.05 mm and the hole is not displaced. When the axis is shifted - only through boring.

What to do if the grade is IT7, and the hole is outside the tolerance? Check the reamer runout (norm ≤ 0.01 mm), allowance value, feed and cutting speed. Most often the reason is too much allowance or spindle runout.

Do you need a reamer for a specific diameter, material or tolerance range? We will select from the catalog or make it according to your drawing.