Tomilson Surface Meter and Taylor-Hobson Surface Meter

1. S.VEDANARAYANA
N.BHARATH
MECHANICAL DEPT
METROLOGY OF SURFACES

2. AUTO COLLIMATOR:
 An autocollimator is an optical instrument for non-contact
measurement of angles. They are typically used to align
components and measure deflections in optical or
mechanical systems.

3. SPIRIT LEVEL:
 Spirit levels are used for measuring the small angles or
inclinations and also enable the position of a surface to
be determined with respect to horizontal.
 A spirit level consists of a sealed glass tube, ground on
its inside surface to a convex form.

4.  SURFACE FINISH:
 Surface finish is a measure of the overall texture of a surface that
is characterised by the surface roughness and waviness of the
surface.
 SURFACE ROUGHNESS:
 Surface roughness is defined as the shorter frequency of real
surfaces relative to the troughs.
 If you observe machined parts you notice that their surfaces has a
complex shape made of a series of peaks and troughs of varying
heights, depths and spacing.

5. FACTORS AFFECTING SURFACE FINISH:
 The surface roughness can be broadly divided into 4 main
categories:
 1.Factors due to machining parameters such as feed rate, cutting
speed, depth of cut.
 2.Factors due to cutting tool parameters such as tool wear, tool
geometry, tool material, tool coating.
 3.Factors due to machine tool conditions such as dry (or) wet
turning, type of cutting fluid etc.
 4.Factors due to work piece material properties such as hardness,
micro structure, grain size and inclusions.

6. ANALYSIS OF SURFACES
 Surface analysis can be done in three ways :
 1.Centre Line Average (CLA) Method.
 2.Root Mean Square (RMS) Method.
 3.Ten Point Height Method.
1.Centre Line Average (CLA) Method:
It is defined as the average values of the ordinates
from the mean line, regardless of the arithmetic signs of the
ordinates.
CLA Value= h1+h2+--------+hn = ∑A
L L

8.  TEN POINT HEIGHT METHOD:
 The average difference between the five highest peaks
and the depth of five lowest valleys within sampling
length.

9. METHODS OF MEASURING SURFACE ROUGHNESS:
 1.Tomilson Surface Meter
 2.Taylor-Hobson-Talysurf Surface Meter
1.Tomilson Surface Meter:
 Principle:
 This instrument uses mechanical and optical means for
magnification.
 Construction:
 In this the diamond stylus on the surface finish recorder is held by
spring pressure against the surface of a lapped cylinder.
 The lapped cylinder is supported one side by probe and other side
by rollers.

10.  The stylus is also attached to the body of the instrument by a leaf
spring and its height is adjustable to enable the diamond to be
positioned and the light spring steel arm is attached to the lapped
cylinder.
 The spring arm has a different scriber at the end and smoked glass
is rest on the arm.

11.  Working:
 When measuring surface finish the body of the instrument is
moved across the surface by a screw rotation.
 The vertical movement of the probe caused by the surface
irregularities makes the horizontal lapped cylinder to roll.
 This rolling of the lapped cylinder causes the movement of the
arm. So this movement induces the diamond scriber on smoked
glass.
 Finally the movement of scriber together with horizontal
movement produces a trace on the smoked glass plate and this
trace is magnified by an optical projector.

13. TAYLOR-HOBSON-TALYSURF SURFACE METER:
 The measuring head of this instrument consists of a diamond
stylus of about 0.002mm tip radius and skid which is drawn across
the surface by means of a motorised driving unit.
 The arm carrying the stylus forms an armature which pivots about
the centre piece of E-shaped stamping. On two legs of the E-
shaped stamping there are coils carrying an A.C. current.
 These two coils with other two resistances from an oscillator. The
amplitude of the original A.C. current flowing in the coils is
modulated because of air gap between the armature and E-shaped
stamping. This is further demodulated so that the current now is
directly proportional to the vertical displacement of the stylus
only.

14.  The demodulated output is caused to operate a pen recorder to
produce a permanent record and a meter to give a numerical
assessment directly. In recorder of this instrument the marking
medium is an electric discharge through a specially treated paper
which blackens at the point of the stylus.

15. THANK YOU