Quality checks: Hands-on Skills Notes for Turner (ITI)

Hands‑On Skills – ITI Turner

Topic: Quality Checks

Quick reference:
Quality checks are systematic inspections performed on a part at the end of each operation (or after a batch) to ensure that the part meets the required specifications, tolerances and functional requirements.

1. Simple Explanation

Purpose:
- Verify that every part produced by the turning operation meets the design or customer specifications.
- Detect defects early to avoid costly re‑work or scrap.
When to perform:
- After each machining operation (e.g., roughing, finishing).
- At the end of a batch or before shipping.
Method:
- Use calibrated measuring instruments (digital/analog calipers, micrometers, height gauges, surface roughness testers, thread gauges, etc.).
- Compare measured values with tolerance limits defined in the engineering drawing or quality plan.

2. Key Points

No	Topic	Why it matters
1	Tolerance & Specification	Defines the acceptable range for each dimension.
2	Measurement Instruments	Accuracy & repeatability are critical.
3	Inspection Plan	Determines what, where, how often, and who inspects.
4	Documentation	Record of measurements, deviations, corrective actions.
5	Common Defects	Roughness, dimensional errors, burrs, surface contamination, improper threading, warping.
6	Correction & Re‑work	If a part fails, decide to re‑work, scrap, or accept as “qualified with defect” (if within tolerance).
7	Quality Culture	Responsibility to check your own parts before passing them on.

3. Worked Example

Scenario:
A turner has machined a cylindrical shaft (nominal diameter 20.00 mm, tolerance ±0.02 mm).
The part is finished and needs a final quality check.

Step‑by‑Step

Prepare the Instrument
- Use a digital dial caliper with an accuracy of ±0.01 mm.
- Zero the caliper on a calibration block.
Measure the Diameter
- Place the caliper jaws on the shaft’s surface.
- Read the measurement: 20.03 mm.
Check Against Tolerance
- Acceptable range: 19.98 mm to 20.02 mm.
- Measured value 20.03 mm → outside tolerance.

Record the Result

Write down:

Part # 001 – Diameter: 20.03 mm (FAIL)
Tolerance: ±0.02 mm
Action: Re‑work required – reduce diameter by 0.05 mm

Re‑work Decision
- Since the part exceeds the upper tolerance, grind the surface slightly to achieve 20.01 mm.
- Re‑measure after grinding: 20.01 mm → PASS.

Final Documentation

Update the inspection sheet:

Part # 001 – Final Diameter: 20.01 mm (PASS)
Remarks: Minor grinding performed.

Take‑away

Even a small deviation can be critical.
Accurate instruments and proper calibration are vital.
Documentation ensures traceability and continuous improvement.

4. Quick Revision Summary

Quality Check = Verification that a part meets its design tolerance.
Key Instruments: calipers, micrometers, height gauges, surface roughness testers, thread gauges.
Tolerance: Acceptable range defined in the drawing; do not ignore it.
Inspection Cycle: What → Where → How → Who.
Common Defects: dimensional errors, surface roughness, burrs, improper threading, warping.
Action on Failure: Re‑work, scrap, or accept if within tolerance.
Documentation: Record measurements, deviations, corrective actions, and approvals.
Safety & Calibration: Always check instrument accuracy before inspection.

Remember: A good turner always checks the part before handing it off. It saves time, money and ensures customer satisfaction.