Control of Inspection, Measuring and Test Equipment

Responsibility

It is the responsibility of the Quality Manager for maintaining our Inspection  Measuring and Test Equipment in good condition and to a known level of accuracy.

All measurement standards, gauges, machines and equipment used to check or control the product to the specified technical requirement will be to a known standard of accuracy.

All reference Standards used in the company will be traceable to National Standards.

Each item of inspection equipment will be recalled at a pre-determined frequency for calibration. The frequency of recall will depend on the purpose, amount of use and historical calibration record of the equipment in question.

A Record of these checks will be maintained on an Excel Spreadsheet, the hyperlinks are below.

External Calibration

Spring load testing machines, gauge blocks and any other equipment used for the specific purpose of in-house calibration will be calibrated outside by a UKAS approved Calibration Service working within their scope, or a similar organisation that has an equivalent level of approval.

Details of these Calibration Service Companies certification and scope will be held on the Approved Supplier File.

Externally calibrated equipment will be identified by the Calibrating Companies UKAS label showing the unique equipment number and its calibration date.

Calibration criteria will be controlled by use of an individual Calibration Record Card, showing a history for each instrument indicating the calibration period and the next calibration date.

Calibration periods may vary according to each instruments use and calibration record.

External calibration records are kept in a folder in the inspection department and are maintained for a minimum of 10 years also please follow the hyperlink to the external calibration index.

In-House Calibration

Equipment will be recalled at a predetermined frequency to be checked in-house against written calibration procedures using gauges and equipment which are reserved solely for this purpose. Recall of appropriate instruments is the responsibility of the Quality Manager or his nominee who will print out a checklist of instruments to be calibrated on a monthly basis from his Access database.

A record of every check carried out on each individual piece of equipment will be maintained. This will contain a least the following information:-

  • Identification reference
  • Method of check
  • Accept/Reject criteria
  • The date when it was last checked
  • The actual measured size
  • The disposition of the equipment following the check.  I.e. satisfactory, adjust, modify, scrap.
  • The date the next check is due.
  • Any other related information

Written calibration procedures for in-house calibration for each type of equipment are appended to these procedures.

Each item of measuring and test equipment used in the factory is calibrated for formal inspection purposes and will always carry its unique identification number. A register of all such equipment will be maintained.

Any equipment that has failed calibration and is not fit for use on formal inspection will be withdrawn from the shop floor or if they still have a use will be marked up as “Indication Only” or “For REF only”.

It is not considered necessary to enter our Press Tools and Checking Gauges into our formal calibration system.

Press Tools once manufactured and producing to the specification will only be checked should a production problem arise.

Internal Calibration

Gauges are used as a production aid only and not for formal inspection and therefore there is no need for them to be formally calibrated.

Were any gauge to be upgraded to the status of a formal inspection gauge then it would be calibrated and entered into the calibration system.

The control of our Press Tools and gauges is managed by marking them with their appropriate drawing number. The locations of tools and gauges are entered onto our computerised master part control record.

The Sales Office has the responsibility for keeping the master part control record up to date.

Press Tools and Gauges when they come to the end of their useful life will be replaced with new tooling and either scrapped or remade into another useful production tool or aid and renumbered.

If any item of checking equipment is found to be out of calibration the Quality Manager will assess the effect that this could have on products previously checked by that equipment. Where he considers this to be significant he will decide if the customer should be informed that he has received suspect material and if it should be recalled.

Internal Calibration External Micrometers

Clean the micrometer with a soft cloth to remove all oil and dirt.

Visually examine for signs of physical damage, sticking of the spindle and thimble, malfunction of the ratchet drive.

Ensure the anvils are perfectly clean and check the zero reading. Adjust if necessary.

Using calibrated slip gauges (C5 & C6) check the accuracy of the micrometer by taking a series of readings across the complete operating range.

It is important to select and use slips which encompass full and partial revolutions of the thimble. For Imperial micrometers, the recommended slip gauge interval in inches are:-

0.1220, 0.2559, 0.3819, 0.4921, 0.6220, 0.7498, 0.8622 and 0.9843

For metric micrometers the following series of slip gauges are recommended in mm for a 25mm span:-

3.1, 6.5, 9.7, 12.5, 15.8, 21.9 and 25mm

For micrometers larger than 25mm or 1-inch span additional slip gauges may be added.

All readings including the original state of the zero prior to any adjustment must be recorded on the calibration record sheet and relate reference gauge block sizes to the micrometer reading.

Reading must correct within the following tolerances according to the smallest scale division:-

Smallest division 0.001” (0.025mm) – accuracy +­ or – 0.0002 (0.005mm) by estimation.

Smallest division 0.0001” (0.002mm) – accuracy + or – 0.00005” (0.001mm) by estimation

All damaged or inaccurate micrometers beyond the scope of our own in-house calibration facility must be withdrawn from service for repair and re-calibration by an outside agency or scrapped.

Please follow the hyperlink to Micrometers calibration Records.

Internal Calibration Vernier Callipers

Clean the vernier with a soft cloth to remove all oil and dirt.

Visually examine for signs of physical damage, special attention being given to the condition of the measuring faces. Check for any sticking of the slider, and malfunction of the adjustment screw if fitted.

Ensure the measuring faces are perfectly clean and check the zero reading, at the same time visually examine the measuring faces for signs of excessive wear.

Using the set of calibrated slip gauges check the accuracy of the external measuring faces over the whole operation range. The deviation of the Vernier reading to the slip block size should be measured at a minimum of a least five approximately equally spaced positions.

All vernier readings including the zero must be recorded on the calibration record sheet and relate to the reference slip block size thereby enabling the errors to be calculated.

Accuracy of Verniers shall be within + or – 0.003 inch (0.07mm) for mechanical instruments and + or – 0.0005 inch (0.012mm) for digital instruments.

All damaged or inaccurate Verniers beyond the scope of our own in-house calibration facility must be withdrawn from service for repair and re-calibration by an outside agency or scrapped.

Please follow the hyperlink to Vernier calibration Records.

 

Internal Calibration Dial Gauges

Clean the dial gauge with a soft cloth to remove all oil and dirt.

Visually examine for signs of physical damage, “stickiness” of the plunger and backlash. Dial gauges are designed to work dry and it is important to ensure the plunger is not oiled or greased.

Examine the physical condition of the contact-point to identify any signs of wear. Worn contact-points can lead to errors and should be replaced as necessary.

Calibration of portable dial gauges is carried out by mounting the gauge in a suitable fixture such that the plunger is above and normal to an engineer’s surface plate upon which calibrated gauge blocks are placed.

Calibration is undertaken at suitable intervals throughout the range of the gauge, typically at every fifth of a revolution of the clock, for gauges having a limited range of two or three revolutions. Gauges with a larger range should be calibrated as per the schedule below.

Divisions on the Dial

0 10 20 30 40 50 60 70 80 90
1st Revolution C C C C C C
2nd Revolution C C C C C
3rd Revolution C C C C C
4th Revolution C C C C C C
5th Revolution C C C C C

Note C = Calibrate

Internal Calibration Dial Gauges

The permissible error for dial gauges vary according to the type of instrument and the magnitude of the interval measured viz:-

Interval of Readings Dial Gauges with 0.001 and 0.0005 inch scale divisions (inch) Dial Gauges with 0.0001 inch scale divisions (inch)
Any 0.01 inch + or – 0.00025
Any half revolution + or – 0.0005 + or – 0.0001
Any one revolution + or – 0.0005 + or – 0.00015
Any two revolutions + or – 0.00075 + or – 0.00025
Any larger intervals + or – 0.001 + or – 0.0007

All calibration readings shall be entered on the calibration record sheet and relate reference gauge block size to dial gauge readings and hence observe the error.

Dial gauges not complying with the above maximum error limits and beyond the scope of our own in house calibration facility must be withdrawn from service for repair and re-calibration by an outside agency or scrapped.