MITUTOYO | Technology | Technical Information

1. Introduction

Dial indicators are among the most popular dimensional gages widely used in various applications that include depth gages and thickness gages in addition to gaging fixtures, height stands, benchtop comparator stands, etc. Accordingly a wide variety of dial indicators are available to meet diverse requirements.
Of the varieties of dial indicatos one-revolution dial indicators have been specifically designed for comparison measurements with features that eliminate reading errors due to miscounting the number of revolutions of the pointer. They also feature a shock-proof mechanism. Because of these features one-revolution dial indicators have been introduced into the industry, especially the automotive manufacturers since their development in 1977. However, they were rather expensive and could not pave the way into global market.
This report introduces newly developed low-priced and high-reliable one-revolution dial indicators.


No.2971	No.2972	No.2973

2. Development Concepts

Our major concerns in developing the new one-revolution dial indicators are enhanced quality, reliability, and environmental durability as well as low-pricing.

Measurement reliability : Preventing human errors
Since the pointer does not turn more than one revolution, reading errors due to miscounting the number of revolutions of the pointer are eliminated.
Indicators with double spaced scale interval are available for ease of reading.

[ Effectiveness of One-revolution Indicators ]

< One-revolution Indicators >	[ Easy to judge as NG ]
< Standard Indicators >	[ Risk of misjudging as OK ] * For a workpiece which is 1mm larger than the normal one, the pointer of standard indicators provide the same reading, thus oversized workpiece may be regarded to be within tolerances if the revolution counter is overlooked.

2)	Long life, environmental resistance, dustproof mechanism
	The new shockproof mechanism protects the gear-train against quick spindle movement. High quality and high performance has been achieved with one piece molding of the dial cover and bezel and the spindle bushing inside the stem for preventing ingress of oil and dust contamination.

3)	Lightweight
	The weight has been reduced by approximately 40%. If used specifically with a bore gage, for example, the new indicator will help to reduce the operator fatigue in long usage.

4)	Cost reduction
	The employment of a new reinforced plastic molding material has achieved high reliability and drastically reduced the cost.

3. New technologies

Plastic case molding

The weight of a case has been reduced by switching from the conventional zinc die casting to the reinforced plastic (PPS + carbon fiber) molding. Also, the structural modification made to the conventional press-fit assembly, which resulted in a one-piece molding of the back plate and stem-inserted molding, has increased the strength of the stem and improved splash resistance.

One-piece case and bushing molding

Having employed a plastic casting for the case, the bushing was also modified from the conventional brass casting to a plastic molding, permitting a one-piece guideway to be formed from a single material. This allows the spindle guide to be positioned inside the case and the stem to be clamped anywhere along its entire range. With this structure, spindle movement is not affected by dust/dirt, should it enter from the lower end of the stem.

The stem can be clamped anywhere along its entire range, thus making the indicator setup easier.

Since the spindle guide is inside the case, spindle movement is not subject to the effects of dust/dirt, even if dust enters from the lower end of the stem. There is no spindle guide bushing in the clamp position, and thus no malfunction will occur due to stem clamping.

Shockproof mechanism

Of the conventional three magnification mechanisms, the pin magnification type was first employed for the 0.01mm graduation indicators. This shockproof mechanism has achieved high durability and high accuracy.

Type	Rack & pinion	Single-gear	Pin magnification
Shockproof	∆	Ο	Ο
Application	0.01mm graduation indicator	One-revolution indicator	0.001mm graduation indicator

Pin-magnification type shockproof mechanism

If the spindle is quickly pushed up, the shockproof mechanism allows the pin to escape from the sector gear to greatly reduce the severity of the shock transmitted to the gear.

Plastic sector gear molding

The use of composite reinforced plastic (POM + whiskers) has improved the sliding capability of the sector gear. The one-piece molding with parts inserted in place of the conventional press-fit assembly has resulted in high accuracy in the assembly process. (First implementation for parts affecting accuracy.)

Hard coating

The dial cover has been given a hard coating to improve scratch and oil (and other chemicals) resistance.

Tests
a: Cover wiped with steel wool
b: Chemicals exposure

Test item	No coating	With coating
a	Many scratches	No scratches
b (trichlene)	Melted	No deformations

4. Specifications

	Graduation(mm)	Measuring range(mm)	Dial reading	Accuracy(μm)		Measuring force (N)
	Graduation(mm)	Measuring range(mm)	Dial reading	Accuracy	Hysterisis	Measuring force (N)
2971	0.01	0.5	25-0-25	± 10	5	1.4
2972	0.01	1	50-0-50	± 12	5	1.4
2973	0.02	1.6	80-0-80	± 16	6	1.4

The outline of the new one-revolution indicator has been given above. Mitutoyo will continue improving the cost-performance of standard indicators by applying the technologies that have been implemented in the new one-revolution indicators.