Gears are the fundamental machine components, mainly used for transmitting power and motion. Though it is a very simple machine element, the manufacturing process is quite challenging to produce a perfect one.
This is why gear metrology and gear inspection devices were developed. The manufacturing error in gear can easily exist in any form. Therefore, while inspecting a gear; the following measurements should be done.
- Pitch measurement
- Run out measurement
- Profile checking
- Lead checking
- Backlash checking
- Tooth thickness measurement
Some types of gear testing tools like gear tooth vernier caliper, David Brown tangent comparator, Skye’s gear tooth comparator, etc are used for gear inspection. The Parkinson gear tester is also one among these gear testing tools.
In this article, let’s learn about Parkinson’s gear tester and its parts, construction, working principle, applications, advantages, and disadvantages.
What is a Parkinson gear tester?
A Parkinson gear tester is a type of rolling gear testing tool used in gear metrology. It is also known as a gear rolling tester. The principle used in Parkinson gear tester is the composite method of gear inspection. When a gear is rolled with a standard gear in a tight mesh, there occurs a variation in the center distance of both gears. The inspection of the variation in the center distance is called a composite inspection of gears.
The tooth to tooth spacing, gear run out, and profile variations of gear can be inspected by the method of composite gear inspection.
The Parkinson gear tester is very popular among other gear testing tools.
Parts of Parkinson gear tester
The Parkinson gear tester is constructed using the following parts.
- Master gear
- Base and Table
- Fixed and floating carriage
- Dial indicator
- Electronic recorders and transducers
Base and Table
The entire instrument setup is placed over the table and the table is placed over the base. The base is a simple rectangular shape metal component that is solid and stable.
Fixed and floating carriage
The carriage which carries the master gear is fixed on the table and the other carriage is set to move using movable rollers. They are frictionless and backlash-free.
There are two spindles in this instrument, and they are fixed normally in both carriages. It helps in mounting gears.
Master gear is a standard gear used for gear inspection in this instrument. It is carried by the rotating spindle in the fixed carriage.
Dial indicator is a type of mechanical comparator. It is used to measure the distance traveled by the floating carriage. To perform simple gear roll tests dial indicators are used.
Electronic transducers and recorders
These electronic devices are used to read the measurement data. In some cases, it is used instead of a dial indicator to measure the output. Normally a Milligraph high-speed recorder with an inductive probe is used.
A scale along with vernier is attached to the base to measure the center distance. It is fixed on the base.
Construction of Parkinson gear tester
The base of the instrument is placed over the rectangular table.
There are two carriages which are placed on the base. Among them, one is fixed and another one is movable. The movable or floating carriage moves with the help of rollers in a horizontal direction.
There is a coil spring in between two carriages. The movable carriage is spring-loaded towards the fixed carriage.
Both the carriages carry a rotating shaft or spindle perpendicular to it.
The spindle in a fixed carriage carries a master gear and another spindle in a floating carriage carries a gear to be tested.
A Dial indicator is attached to the base in a horizontal position to keep contact with the movable carriage. In some cases, dial indicators are replaced by electronic transducers and electronic recorders.
Working of Parkinson gear tester
Initially, the instrument is calibrated and equipped with a master gear and testing gear in their respective spindles.
Both the gears are maintained in the mesh condition due to the spring force applied between the carriages.
The gears mounted on the spindles are free to rotate. Due to the imperfections in the testing gear, the sliding carriages move in a horizontal direction.
The horizontal displacement of the sliding carriage is sensed and indicated by the dial indicator.
The center distance is measured by a scale placed on the carriage and Vernier on the other side.
The accuracy of Parkinson gear tester is ±1 micron.
The dial indicator can be replaced by an amplifying device and an electronic recorder as used in the talysurf surface meter. The errors are traced and reproduced in two types of chart or graph sheet with the magnified radial errors. It is in the form of circular or rectangular charts.
The typical charts traced by the recorder are shown below.
- A faulty gear is denoted by the unsatisfactory circle.
- A moderate gear is denoted by the moderate circle
- A perfect gear is denoted by the fully satisfactory circle.
Advantages of Parkinson gear tester
The Parkinson gear tester has certain following advantages.
- It has a solid and rigid design.
- It is easy to operate.
- The replacement of dial indicators with electronic transducers and recorders for complicated gear roll tests is an added advantage.
- A high degree of magnification can be achieved in this instrument.
- The accuracy of this instrument is about ±0.001mm.
- All types of gear (bevel, helical, and worm gear) can be inspected using a Parkinson gear roll tester.
- Quick results can be obtained by using this instrument
- .It requires low maintenance and less space.
- Since it is lightweight, it can be easily portable from one place to another place.
Limitations & Disadvantages of Parkinson gear tester
The Parkinson gear tester has certain following limitations & disadvantages.
- The gear inspection of this instrument mainly depends on the master gear.
- Rolling gear tests do not reveal all types of errors.
- Errors are not clearly differentiated to know the types of errors in gear.
- Low friction occurs during the movement of the floating carriage.
- The high sensitivity of the sensing unit should be maintained.
- The maximum and minimum diameter of gears that can be tested in this instrument is 300mm to 150mm.
Applications & uses of Parkinson gear tester
The Parkinson gear tester has certain following uses & applications.
- It is used to detect and measure the errors in tooth form, pitch, and pitch line.
- It is used for shop floor measurements to inspect the manufactured gears.