"We can hold H7" is a claim, not evidence. The evidence is a size report with a distribution, a roundness measurement, a roughness trace, a capability figure with a sample size behind it, and a gauge whose calibration can be checked.
This page lists the eight items worth requesting before a tool is approved, how to read each one, and the signals that a report was produced to satisfy a checklist rather than to describe a process.
The eight items are: size report, roundness and cylindricity, roughness, capability with sample size, gauge and calibration, material and grade traceability, regrind record, and a signed release with a non-conformance path.
Three reading rules catch most weak submissions: a single value with no spread means the measurement was insufficient, a capability figure without a sample size is not a capability figure, and a report without a gauge serial cannot be rechecked.
The list is written so it can be pasted into a purchase requirement. Not every item is available from every supplier, and the page says which ones HENTRY can supply and which have to be agreed case by case.
Why "H7" is not evidence
A tolerance class describes a band, not a distribution. Two suppliers can both hold H7 with processes whose spreads differ by a factor of three, and the difference shows up in scrap and in first-article arguments, not in the class.
Evidence moves the acceptance decision earlier. Instead of discovering at goods-in that the bore is at the edge of the band, the buyer sees the distribution before the tool is released, and the decision is made on data rather than on a promise.
It also changes the conversation after a failure. With a size report and a gauge serial, a disagreement about whether the tool or the machine caused a bore is a measurement question that can be settled. Without them, it is a matter of opinion.
The cost of the evidence is small. Most of the eight items are produced anyway during a first article; the only change is that they are written down and sent instead of being filed.
What the evidence cannot do is guarantee the future. A capability figure describes a process at a point in time, on a machine, with a material batch. It is evidence of what happened, not a warranty of what will happen.
The eight items
The table lists each item with the reading point that matters and the signal that it is missing or manufactured.
| Evidence item | What to read | Missing or fake signal |
|---|---|---|
| Size report | Three diameters per part, at entry, middle and exit, with the gauge identified | One diameter per part, or a single part, or values that repeat exactly |
| Roundness and cylindricity | A measured value per sample, not a pass or fail tick | A statement that the bore is round, with no instrument named |
| Surface roughness | Ra with the cut-off length and the direction of measurement | An Ra value with no cut-off, or a value quoted from a catalogue |
| Capability | Capability index with the number of parts, the machine and the date | An index without a sample size, or a sample of five |
| Gauge and calibration | Gauge type, serial number and calibration due date | A gauge described by type only, or a calibration certificate for a different instrument |
| Material and grade | Workpiece material and hardness, insert grade or PCD source, batch reference | A grade without a batch, or a substitution note after the fact |
| Regrind record | Regrind count, diameter before and after, remaining allowance | No record on a tool that has been in service |
| Release and non-conformance | Signed release with the specification it was released against, plus the path for a non-conforming part | A signature with no specification, or no defined escalation |
Three of these are produced by the tool maker, three by the machine shop running the tool, and two are joint. The split matters because a buyer who asks the tool maker for a capability study is asking for something the tool maker cannot produce alone.
For a custom tool, the practical package is the tool drawing, the material and grade certificate, the geometry inspection and the first-article results from the customer's machine. That package is what HENTRY can supply directly; the machine-side capability figures come from the customer's own run.
Which items matter most depends on the route. A reaming route lives or dies on size distribution; a boring route on adjustment records and insert traceability. The route matrix that decides which of the two applies is on hole route selection by tolerance and volume.
How to read each one
Three reading rules cover most of the weak submissions we see, and each one is a question that can be asked in a single email.
The first rule: a single value with no spread means the measurement was insufficient. A bore that is 25.003 mm once is a data point; ten bores between 25.001 and 25.012 is a process.
The second rule: a capability figure without a sample size is not a capability figure. Thirty parts is the usual minimum for a first look, and the number should be next to the index, not in an appendix.
The third rule: a report without a gauge identifier cannot be rechecked. If the gauge cannot be identified, the number cannot be reproduced, and an unreproducible number is not evidence.
Two more rules are worth adding for reground tools. A regrind record without the diameter before and after is a service log, not a geometry record. And a remaining-allowance figure without the pre-hole it will run against is a number without a denominator.
Read the surface value with the cut-off and the direction. An Ra measured across the feed marks and one measured along them are different numbers on the same bore, and a report that omits the direction cannot be compared with another supplier's.
What to write into your PO
The clauses below are example text, not legal advice. They are written to be edited by the buyer's quality and legal functions before use.
Clause one, first article: "First article of 30 consecutive parts. Size at three axial positions per part, roundness and cylindricity on five parts, Ra on five parts with cut-off and direction stated. Results to be supplied with the shipment."
Clause two, gauge: "All dimensional results to identify the gauge by type and serial number, with calibration status valid at the date of measurement."
Clause three, traceability: "Tool material grade and batch to be recorded on the certificate; any substitution requires written approval before shipment."
Clause four, non-conformance: "A part outside the specified band to be quarantined, reported within one working day, and dispositioned in writing before replacement parts are shipped."
Clause five, regrind: "Reground tools to be supplied with diameter before and after, regrind count and remaining allowance relative to the specified pre-hole."
The clauses are deliberately about evidence rather than about penalties. A supplier who can produce the evidence usually also meets the band; a supplier who cannot is the one the clauses are designed to reveal.
Where each item comes from
Knowing who produces each item prevents a request that cannot be answered and a delay that looks like reluctance.
The tool maker produces the geometry inspection, the material and grade certificate, the regrind record and the release signature. These are properties of the tool and travel with it.
The machine shop produces the capability figures, the in-process size distribution and the surface measurements, because they depend on the machine, the fixture and the material being cut.
The gauge and calibration status is joint: the instrument belongs to whoever measures, and the calibration record belongs to that party.
The practical consequence is that a purchase requirement should ask the tool maker for tool-side evidence and the machine shop for process-side evidence. Asking one for the other produces either a refusal or a document that was not measured.
For a first article on a new tool, both sides are needed. The tool-side package proves the tool is what was ordered; the process-side package proves the combination holds the band.
The boundary between this and an audit
Requesting data is a desk exercise. An audit is a site visit with a checklist, and the two answer different questions.
The data request answers whether this tool, on this machine, held this band. The audit answers whether the supplier's system will keep doing so across tools, shifts and personnel.
The order is usually data first, audit second. A supplier whose first-article package is complete and internally consistent rarely needs an audit to justify a trial order; a supplier whose package is thin is a candidate for one.
The trigger for escalation is specific: two or more evidence items missing without a credible reason, or one item that cannot be reproduced on request. That is the point at which a site visit earns its cost.
There is also a scope question. A data package describes one tool on one bore; an audit describes a system.
A buyer who has not yet settled whether size or position is the hard requirement will ask for both and learn from neither, which is why the requirement on position tolerance versus size tolerance comes first.
This page does not cover the audit itself. It covers the package that makes an audit unnecessary for most suppliers and targeted for the rest.
The inspection pack for PCD reamers is set out in PCD reamer inspection pack, and the validation sequence for a new tool is in sample validation process.
What published sources say about this
These pages were used for the measurement and capability logic. Each is cited for what that page states, under its own conditions.
- What is Process Capability? (NIST/SEMATECH e-Handbook of Statistical Methods): the comparison of process spread with specification limits, the basis for asking for a capability index rather than a pass statement.
- What are the issues for characterization? (NIST/SEMATECH e-Handbook): why a measurement has to be defined with its method and its control programme, the reason a gauge serial belongs on the report.
- How are bias and variability controlled? (NIST/SEMATECH e-Handbook): the difference between a gauge that repeats and one that is correct, the point behind calibration status.
- What are control charts? (NIST/SEMATECH e-Handbook): time-ordered data as the way to see whether a process is stable, which is what a 30-part first article is trying to establish.
- Dimensioning and Tolerancing (ASME Y14.5): the definitions a report has to be read against, including roundness, cylindricity and position.
- Reamers, machine reamers (toolmaker technical overview): reamer geometry and guide features, the tool-side characteristics a geometry inspection should confirm.
- Digitalised regrinding management (toolmaker report): reconditioning described as a significant expense whose registration and turnaround are the critical parts, the reason a regrind record is on the list.
Outbound references are listed because the checklist depends on them, not as endorsements. The eight items and the reading rules are HENTRY's convention and are not taken from these sources.
Frequently asked questions
Can HENTRY supply all eight items?
The tool-side items, yes: geometry inspection, material and grade certificate, regrind record and release signature. Capability figures depend on the customer's machine and are produced jointly during the first article.
Where an item is not available, the reply will say so rather than supplying a document that was not measured.
How many parts make a credible capability figure?
Thirty consecutive parts is the usual minimum for a first look; fewer than that gives an index with a wide confidence interval.
The number of parts belongs next to the index. A capability figure presented without its sample size should be treated as a claim.
What if the supplier refuses to provide a gauge serial?
Ask for the gauge type and the calibration certificate instead, which is often enough to identify the instrument.
A refusal with no alternative is a signal about the reporting system, not about the bore.
Does a capability index guarantee future parts?
No. It describes a process at a point in time, on a machine and a material batch.
What it does is make the first article reviewable, which is a different and more useful guarantee than a promise.
Where does this fit against a supplier audit?
Data first, audit second. The package answers whether this tool held this band; the audit answers whether the system will keep doing so.
Two missing items or one unreproducible result is the usual trigger for escalating to a site visit.
If the capability data leads to a first-article failure rather than an approval, the process that follows is set out in nonconformance and 8D, and the on-site version of the same evidence is tested by the supplier audit checklist.
Updated 13 November 2026: first publication. Scope: the eight evidence items to request before approving a tool, the reading rules for each, example purchase-order clauses and the boundary between a data request and an audit. The PO clauses are example text requiring business and legal review.