What is Tomlinson surface meter?
Tomlinson surface meter is a surface finish measuring instrument and it was designed and developed by Dr. Tomlinson. It is based on the principle of mechanical-cum-optical magnification method.
Whenever a component is produced by various machining or manufacturing process, certain surface irregularities will be there. This is very common while manufacturing a machine component. A component with surface irregularities can cause many difficulties while using it. These surface irregularities should be inspected and corrected.
The machined component with surface roughness or irregularities can be inspected and measured by two various methods such as,
- Inspection by comparative methods
- Direct measurement method
In the comparison method, the surface roughness of a component is examined by the observation of its surface.
In the direct measurement method, a stylus type device is used for inspecting the roughness parameter. The various types of instruments used for the direct measurement method are
- Stylus probe instrument
- Tomlinson surface meter
- Taylor Hobson Talysurf
Let’s see in detail about Tomlinson surface meter in this article.
Parts of Tomlinson surface meter
The Tomlinson surface meter is constructed using the following parts.
- Diamond probe
- Smoked glass screen
Skid is placed on the workpiece and it is carried by the body of the instrument. It helps in positioning the stylus.
The stylus is similar to the plunger, used as a sensing element to detect the surface roughness of the component. It is constrained to move in a vertical direction.
At the bottom of the stylus, there is an adjustable diamond-tipped probe. The height of the diamond probe is adjusted by using a skid at the bottom. The diamond probe tip is about 2 microns in radius.
This instrument consists of a helical coil spring and a Leaf Spring. Both springs are used to hold and attach the stylus to the frame.
A moving arm is attached to the looped cylinder. It is placed in between the stylus and fixed rollers. The arm is also called a light lever.
The body act as a support for this instrument. One end of the helical spring and leaf spring is fastened to the body for support. The fixed rollers are also attached to the body.
A diamond scriber is carried by the arm at its tip. It is placed against the smoked glass screen.
Smoked glass screen
A smoked glass screen helps to trace the surface texture of the component with the help of a diamond scriber. It is also called black glass in other words. It rests on the needlepoint of the diamond scriber.
These are the following parts used for the construction of Tomlinson surface meter.
Construction & working principle of Tomlinson surface meter
A stylus with a diamond probe and skid are attached together and they are restrained to move in a vertical direction. They are restrained by a coil spring and a Leaf Spring.
The stylus is held by the tension of both springs against the lapped cylinder. The tension in the Coil spring is the same as the tension in the leaf string.
An arm with a diamond scriber is attached to the lapped cylinder. This lapped cylinder is placed against a pair of fixed rollers and a stylus.
A smoked glass screen is rested on the diamond scriber to trace the surface of the texture of the component or workpiece.
When a component with surface roughness or surface irregularities is kept under the diamond probe, the stylus moves in a vertical direction (up and down). This vertical motion of the stylus depends on the roughness or irregularities on the surface of the component.
Since the stylus is held by springs on both sides, a similar tension is created in both coil spring and leaf spring due to the vertical displacement of the stylus.
These two tension forces of both springs hold the lapped cylinder along with the arm in the position between the stylus and fixed rollers.
The vertical displacement of the stylus causes the lapped cylinder to roll. This motion is further magnified by the arm.
The diamond scriber carried by the arm traces the profile on the smoked glass screen depending on the surface roughness or irregularities on the workpiece.
The traced profile along with the smoked glass screen is transferred to a profile projector (type of optical comparator) for further magnification. Under the profile projector, it is further projected to X50 to X100 magnifications to examine the exact surface texture of the component.
The stylus must place transversely to the surface of the component to trace the profile. This can be achieved by adjusting the body of the instrument with the rotating screw driven by a synchronous electric motor.
This is how the Tomlinson surface meter works. Now lets see about its applications, advantages, and disadvantages.
Advantages of Tomlinson surface meter
The Tomlinson surface meter has certain following advantages.
- It is simple and compact in design.
- It gives reliable results.
- It is comparatively low in cost.
- Any roughness parameter can be measured using this instrument.
- Higher magnification can be achieved due to the principle of the mechanical optical magnification method.
Disadvantages of Tomlinson surface meter
The Tomlinson surface meter has certain following disadvantages.
- Wear and tear of components can occur due to mechanical movements.
- Since it is delicate it should be handled with care.
- Though it gives reliable results the speed of operation is comparatively slow.
- Due to its slow operation speed, it is not suitable for continuous and rapid use, especially in shop floor usage.
Applications & uses of Tomlinson surface meter
The applications of Tomlinson surface meter are listed below.
- It is used for inspecting surface roughness where the direct measurement method is preferred.
- It is mostly used in automotive parts manufacturing industries, machinery parts manufacturing industries, etc to inspect the surface roughness of the component after the machining process.
- It is also used in laboratories for surface metrology.