Bore gauge with dial indicator 0.01 mm

Internal gauge for measuring internal dimensions such as cylinders and bores for dimensional accuracy, ovality, and taper. Self-centering with interchangeable probes. A large measuring range can be covered by exchanging the fixed measuring stop. Measurements with very small error margins are possible through the use of the precise dial gauge.

• with dial gauge: measuring range 3 mm, reading 0.01 mm
• with shock protection housing for dial gauge
• fixed steel measuring bolt
• movable carbide measuring bolt
• incl. case

Measuring range (mm)	Inserts	Discs	Extensions	Measuring depth
18 - 35 mm	9	1	-	150 mm
35 - 50 mm	4	4	-	150 mm
50 - 160 mm	12	4	1	150 mm
160 - 250 mm	5	5	1	400 mm
250 - 450 mm	4	5	2	400 mm

Measuring with the Internal Gauge

Construction
The internal gauge is a comparative measuring device for measuring internal dimensions, mostly bore diameters. It consists of a measuring head and a shank, at the end of which the dial gauge is clamped.
A fixed measuring stop is mounted on one side of the measuring head. This can be exchanged, thereby adjusting the measuring range of the device. This allows large measuring ranges to be covered. Opposite it is a movable measuring bolt, whose movement is transmitted to a rod in the shank and thus to the measuring bolt of the dial gauge. Depending on the model of the internal gauge, the travel of the movable measuring bolt is 1-3mm.

a movable measuring bolt
b fixed measuring stop
c spring-loaded stop bridge with cradle-shaped ends
d shank
e deflection of the measuring bolt movement by lever

Pre-setting
Measurements with very small error margins are possible with the internal gauge, provided that the pre-setting and the measurement are carried out correctly. Before use, the internal gauge is pre-set as follows:
The interchangeable measuring stop is mounted, with which the length of the measuring head most closely matches the dimension to be measured. The dial gauge is inserted with some pre-tension (approx. 1-2 rotations) and clamped.
Since the dial gauge only determines the deviation of a known dimension, a precise internal dimension must be defined using a reference dimension. The reference dimension can be, for example, an external micrometer, a setting ring, or another setting device. The scale of the dial gauge is now set so that the 0 on the scale aligns with the pointer's position at the reversal point. This should be done as precisely as possible to exclude measurement errors.

Measurement
The measuring head is centered in the bore by the spring-loaded centering bridge on the side of the movable bolt. In the horizontal position, the measuring head must be aligned manually to find the reversal point of the dial gauge: The measuring device is gently swayed back and forth until the maximum deflection of the dial gauge pointer (reversal point) is found. This is the desired measured value.

a Set measuring device to reference dimension with setting ring or gauge block; set dial gauge to zero
b Insert measuring head into the bore; determine the bore dimension at the reversal point of the pointer by a swivel movement; read the deviation

Evaluation
The measured dimension must now be compared with the pre-set reference dimension. If the reversal point of the pointer is after 0 on the scale, the dimension is smaller. The measured value is thus subtracted from the reference dimension. If the reversal point is before 0, the dimension is larger, and the measured value is added.
Measured size = Reference dimension - Measured value

Example:
The internal gauge was pre-set to 70mm, and a deviation of 0.02mm was measured. The diameter of the bore is therefore 70mm – 0.02mm = 69.98mm.