Reamed holes

Specify the hole, then the process

Reaming finishes an existing hole. Specify diameter, form, location and surface texture separately from the process name.

At 10.000 mm, the cited ISO 286-2 extract gives H7 limits 10.000–10.015 mm. A nominal size just above 10 mm falls in the next band, with +18 µm upper deviation through 18 mm. With the example 9.990–9.995 mm pin, the 10 mm hole has 0.005–0.025 mm diametral clearance, before form and location effects.

Gühring's reaming guidance places preparation of the drilling position and path before the reaming operation and discusses pre-hole allowance, speed, lubrication and tool selection. Those are linked process inputs, not substitutes for a dimensioned finished-hole requirement. No technical revision date was verified on the live page. Gühring reaming tools and process guidance

For a dowel, bushing, shaft or bearing interface, define what the hole must do. Select the fit and geometry against the mating component and assembly; do not choose H7 merely because it appears in a tool catalogue.

Distinguish size, fit and geometric accuracy

DIN's public record identifies DIN EN ISO 286-2:2019-09 as the national publication incorporating ISO 286-2:2010 plus Cor 1:2013, with tables of standard tolerance classes and limit deviations for holes and shafts. Preserve those edition distinctions instead of treating the 2019 publication as a new ISO technical edition. DIN Media, ISO tolerance tables

A size tolerance is not a complete geometric or functional specification. A diameter result at one location does not establish axis location or the entire bore's form. State additional requirements only where needed for function and make them inspectable.

A bounded H7 example

Ganter's supplier extract of ISO fundamental tolerances lists H7 = 0 to +15 µm for nominal sizes over 6 through 10 mm, and 0 to +18 µm for over 10 through 18 mm. No technical issue date was verified on the extract; use the contracted standard for acceptance. Ganter ISO 286-2 extract

At 10.000 mm H7, the listed size limits are therefore 10.000–10.015 mm. A nominal size just above 10 mm falls into the next band. Do not apply one fixed “H7 tolerance” to every diameter.

Original fit arithmetic: assume the accepted mating pin is separately specified at 9.990–9.995 mm. Diametral clearance is minimum 10.000 − 9.995 = 0.005 mm and maximum 10.015 − 9.990 = 0.025 mm. This simplified size stack does not establish insertion force, contact behavior, alignment or performance after temperature changes. The pin limits are illustrative, not a claimed standard shaft class.

Reamer size and stock allowance

Presto's Reaming Practice distinguishes the intended H7 hole size from the reamer's own manufacturing tolerance. Its page also says reaming allowance depends on material, with different requirements for harder materials and very soft steel. Do not interpret its product-focused H7 wording as proof that every reamer produces an H7 hole. No technical issue date was verified. Presto reaming practice

Specify whether stock allowance is on diameter or per side. For an illustrative finished diameter of 10.000 mm and pre-hole diameter 9.800 mm, nominal diametral allowance is 0.200 mm, corresponding to 0.100 mm radial removal only for concentric circular geometry. This is arithmetic, not a recommended allowance for an unspecified material or tool.

Gühring publishes a material/diameter-dependent allowance table as well as general preparation guidance. Use the selected tool's application data and the measured pre-hole rather than elevating a generic undersize value to a universal rule. Gühring reaming allowance guidance

The pre-hole needs the correct location and adequate cleanup stock. Do not assume reaming will rescue an incorrectly located or distorted feature without a demonstrated process. Review the preceding operation when repeated reaming adjustments fail to produce acceptable holes.

Blind holes, through holes and tool geometry

A blind hole must provide room for the tool's cutting lead, required finished cylindrical length and chip management. Define the controlled bore depth independently of the deepest tool/drill point. If a mating pin must seat near the bottom, state the relevant usable depth and bottom clearance explicitly.

MAPAL's high-performance cylindrical-shank reamer range includes internal coolant and application-specific designs for through and blind bores. This establishes a named product capability, not that any reamer or flute design is suitable for both. The webpage has no verified technical revision date. MAPAL high-performance reamers

Select lead geometry, flute design, holder and coolant delivery for the actual material and hole. Confirm access, interruptions, chip exit and clamping with the machinist. Avoid a universal cutting speed, feed or bottom allowance detached from that selection.

Process control and inspection

Reamer diameter alone does not establish process capability. Review the complete setup: tool condition, runout/alignment, holder, workholding, material consistency, pre-hole and coolant. Gühring's troubleshooting page identifies insufficient stock removal and incorrect clamping among causes of chatter marks; a surface defect may therefore require a process correction rather than a different nominal hole callout. Gühring chatter troubleshooting

At inspection, separate size, form and location results. Choose a method appropriate to the characteristic: a functional plug, a local diameter measurement and a coordinate measurement answer different questions. Agree acceptance limits, measurement conditions and the stage of inspection when heat treatment, coating or another finishing operation follows reaming.

Keep entry/exit burrs and chamfers under control where they affect assembly. An entry chamfer does not change the specified useful cylindrical length unless the drawing defines it that way. Likewise, a satisfactory fit with one sample pin does not independently demonstrate all hole limits or long-term production capability.

Release record

1. Define the hole's size, usable extent, location and functional fit.
2. Agree material condition, preceding operation and reaming route.
3. Select application-specific tooling, allowance and process data.
4. Verify the required characteristics on representative finished parts.
5. Preserve inspection results and revisit the process when inputs change.

For agent-readable records, store finished-hole limits, reamer designation and pre-hole allowance separately. Retain units, diameter/radial basis, source edition and inspection stage. A catalogue target, a measured result and a contractual limit should remain distinguishable.