Measuring Instruments for Large Dimensions

Large sizes in mechanical engineering mean dimensions in excess of 500 mm. Besides various measurement procedures like those that apply large internal or external micrometers with two-point contact, tape rules (wrapping round the outside diameter), V-bases, rotating measuring disks (rolling-contact) and optical systems (triangulation with theodolites), resort is often to make use of simple testing means like fixed gauges (inside calliper gauges), gauge blocks combinations or telescopic adjustable gauges.

For large dimensions from 250 mm up to several meters, TESA offers various types of measuring instruments that have long proven their value in practical use. Here's an example of a proportional relationship. With a bore of 1200 H7, the tolerance zone is 0,1 mm. Reducing both values by a factor of 100 would give a manufacturing tolerance as low as 1 μm. Of course, things are not as simple, but this example gives some ideas about the proportions.

Whatever the sizes, from a simple distance between two surfaces parallel to one another to large diameters, their measurement is always a challenge to take up. Apart from the usual influences, which are proportional to the size and add to your contributions in the uncertainty budget, those due to gravity play a key role in distortion.