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Request a Proposal โBefore CNC controllers calculated Reaming Allowance automatically, machinists used cardboard slide calculators โ Widia famously distributed tens of thousands of these in the 1970s. Every tooling rep had a pocket full of them. The math was the same, but the constraints were wildly different: HSS tooling maxed out at 30-40 SFM in steel, and feed rates were limited by machine rigidity, not coating technology.
The Ingersoll coating revolution in the 1980s โ TiN first, then TiCN, TiAlN, and eventually AlCrN โ changed everything. Suddenly, Reaming Allowance could be pushed 200-300% higher without sacrificing tool life. Korloy's introduction of submicron carbide substrates in the 1990s further expanded the window: finer grain structures meant harder tools that could still absorb the shock of intermittent cuts.
In 2026, Ingersoll and Korloy both offer cloud-based Reaming Allowance optimization via their NOVO and ToolGuide platforms. Widia's CoroPlus system integrates directly with Starrag and Grob CNCs for real-time adaptive control. The slide calculator has been replaced by AI-assisted CAM, but the core principle remains: the right number = the right cut.
A reamer removes a small, controlled amount of material to achieve precise hole size and surface finish. Too little stock and the reamer rubs; too much and it overloads, produces a bell-mouthed hole, or breaks. This calculator gives the optimal stock allowance.
H7 (e.g., 10.000-10.015 mm) is standard with a quality reamer in good condition. H6 is achievable with carbide reamers and rigid setup. The reamed hole is never perfectly round -- expect 1-3 ยตm out-of-roundness due to spindle runout and uneven chip loading.
Boring heads are adjustable and can correct position error; reamers follow the existing hole. Use boring for position-critical holes (true position under 0.05 mm). Use reaming for high-volume, consistent-diameter holes where position is less critical.
Common causes: excessive spindle runout, built-up edge on the reamer, wrong stock allowance, misaligned tailstock or turret, and worn guide bushings. Check runout first -- a reamer floating in a worn collet will always cut oversize.
Enter the finished hole diameter. The calculator recommends the stock allowance and the pre-ream drill size. For critical holes, drill undersize, then bore to within reaming allowance, then ream -- this corrects position error before the reaming pass.
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Use the calculator freely. If the result points to a tooling or process problem, we can source the exact carbide tooling you need from vetted factories in China. Compare factory-direct pricing.
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