SPC for Precision Machining

• Control charts and capability

  X-bar/R and X-bar/s, Phase I limits from the first 25 subgroups, Cp, Cpk, Pp, Ppk and observed ppm per characteristic, two-sided and upper-limit-only (flatness, true position, surface roughness).

• Run-rule and anomaly detection with labels

  the six Western Electric/Nelson flags are in the file; the true shift is too, so detection rate, false-alarm rate and average run length can be measured rather than assumed. A benchmark for ML detectors (CUSUM, EWMA, isolation forests, sequence models) against a known truth.

• Root cause analysis

  join a signal to the cause active on its machine, the material lot, the operator, the hours since the last tool change and the days since maintenance.

• Tool wear and predictive maintenance

  shaft diameters and surface roughness grow and bores shrink with the hours on a tool, and reset at each change; within-subgroup spread widens as a machine goes longer without maintenance.

• Measurement system analysis

  each gauge has a crossed GR&R study (ANOVA or range method) and a calibration history; readings sit on the gauge's own resolution, so a coarse gauge shows up as it does on a real chart.

• Teaching and dashboards

  realistic enough for an SPC course, a Six Sigma project, a Power BI/Tableau quality dashboard, or a MES/QMS demo database.

• subgroups.active_cause_idThe assignable cause in force when the subgroup was sampled, if any.285 distinct, 95% empty
• subgroups.true_cause_shift_sigmaThat cause's shift of the mean, in within-subgroup sigma.-4.36 to 4.62, mean 0.021
• subgroups.true_tool_wear_sigmaTool wear since the last change, in sigma.-0.8 to 0.8, mean 0.14
• subgroups.true_lot_shift_sigmaThe material lot's hardness effect, in sigma.-0.45 to 0.48, mean 0.016
• subgroups.true_operator_shift_sigmaThe operator's setup bias, in sigma.-0.32 to 0.21, mean 0.0048
• subgroups.true_driftThe process mean's own slow drift (AR(1)), in sigma.-0.29 to 0.27, mean 0.00021
• subgroups.true_process_meanThe true process mean at that moment, in the characteristic's unit.-0.12 to 156.1, mean 29.13
• subgroups.noise_factorHow much wider the within-subgroup spread is as maintenance ages.1 to 1.2, mean 1.06
• assignable_causes.magnitude_sigmaEach cause's size, with its category, start, end and direction.0.45 to 4.62, mean 1.55

• 5.0% of subgroups were sampled while an assignable cause was active; 94% of the Phase II subgroups under a cause of 1.5 sigma or more trip at least one rule, against 21% of those under none (tool wear, lots and drift still move the mean there, and are labelled).
• Rule 1 false-alarm rate, stable Phase II: 0.74% (theory 0.27%); estimated limits from 25 subgroups and an autocorrelated process put it above the textbook 0.27%, as they do in practice.
• 0.33% of readings are out of specification. 14% of characteristics have Cpk below 1.0 and 61% are at 1.33 or better; 25% are marked critical to quality.

• every key resolves and every primary key is unique; each characteristic's machine and gauge are on its part's line, each operator on the subgroup's line, each lot belongs to the part and was received before it was used;
• every subgroup has exactly 5 readings; X-bar, max, min, range and s re-add exactly from the readings;
• control limits, Cpk and Ppk recompute from the subgroups and readings; all six rule flags recompute with 0 differences;
• each feature is measured on a gauge that suits it, and every reading sits on its gauge's resolution;
• a cause is only recorded on a subgroup sampled inside that cause's window on that machine;
• the gauge R&R trials recover each gauge's stated %GR&R;
• it reads like a real shop: machines suit their line's process and tools suit their machine; materials and sectors suit the part (no aluminium orthopaedic screws); drawing sizes are whole or half millimetres with standard tolerance bands, and flatness, position and Ra limits are drawing grades; balloon numbers never repeat on a part; hardness is on the scale each material is tested on (HRC for 4140, 17-4PH and Ti-6Al-4V; HRB for 316L, 6061 and brass) inside that grade's usual band; the operator on a chart works that shift; each corrective action answers its cause; gauges are calibrated about once a quarter and one found out of tolerance is always adjusted.

• readingsEvery individual measurement, on its gauge's resolution, with out-of-spec flag414,750 rows · 8 cols
• subgroupsOne row per n=5 sample: X-bar, R, s, Western Electric flags, the lot, operator, hours since tool change, and the TRUE cause of any shift82,950 rows · 36 cols
• tool_changesEvery insert, cutter and drill change or wheel dress, suited to the machine, and why13,000 rows · 5 cols
• gauge_rr_trialsA crossed gauge R&R study per gauge: 10 parts x 3 appraisers x 3 trials3,240 rows · 7 cols
• material_lotsBar-stock heats per part: supplier, received date, hardness on the material's own Rockwell scale536 rows · 8 cols
• assignable_causesEvery special cause: machine, category, start, end, size in sigma, direction, corrective action, CAPA300 rows · 10 cols
• maintenance_eventsPreventive, corrective and spindle work with downtime by kind of job240 rows · 5 cols
• characteristicsThe drawing's controlled features: spec limits, gauge, Phase I control limits, Cp/Cpk, Pp/Ppk, observed ppm158 rows · 40 cols
• gauge_calibrationsQuarterly calibrations: as-found error against the gauge's permitted error, result, adjustment72 rows · 7 cols
• operatorsOperators by line and home shift, experience, certification, setup bias72 rows · 7 cols
• partsMachined parts: family, a material and sector that suit it, drawing revision, annual volume by sector40 rows · 8 cols
• gaugesOne CMM, air bore gauge, micrometer and profilometer per line: resolution, %GR&R, repeatability and reproducibility36 rows · 10 cols
• machinesCNC lathes, machining centres and grinders, each suited to its line, with its own capability factor and PM interval36 rows · 7 cols
• production_linesMachining lines and their process family9 rows · 5 cols
• plantsThree plants and their region3 rows · 3 cols

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