page 121

• The symbol below can specify how the roughness is to lay,

From this end use this symbol

From the side use this symbol

Other Symbols are,

across both

multi(bumpy)

radial to centre

circular to centre

X

M

R

C

•Standards CLA/Ra values used on drawings are: 1, 2, 4, 8, 16, 32, 63, 125, 250, 500 and 1000

in.

•Stylus travel is perpendicular to the lay specified.

•These symbols can be related to the newer GD&T symbols

11.3 OTHER SYSTEMS

• The Root Means Squared (RMS) System (also known as Rq) is not commonly used in Canada,

page 122

h5 h6	hn	Mean line

h1 h2 h3 h4

l

RMS = Rq	h12 + h22 + h32 + … + hn2
	= ----------------------------------------------------
	n

**Note: This value is typically 11% higher than CLA or Ra

• The Peak to Valley method cuts the peaks off the wave, and then uses the band between to determine the roughness. This method is not commonly used in Canada.

p1	p2	p3		p4
L1
				h
L2
v1		v2	v3	v4
		l

The two parallel lines L1 and L2 are positioned such that they cut off the peaks and valleys, given the mathematical constraints,

∑ P = 0.05l

∑ V = 0.10l

h is the measure of peak to valley height

page 123

• A simple table that basically outlines the process capabilities of a number of processes is, [ANSI B46.1-1962]

process

2000

1000

Roughness Height ( in.)

500

250

125

63

32

16

0.5

8

4

2

1

sand casting

-700

hot rolling

curve

forging

perm. mold casting

-600

investment casting

the

extruding

by

cold rolling, drawing

designed

die casting

-500

flame cutting

snagging

finish

sawing

planing. shaping

-400

drilling

surface

chemical milling

electrical discharge machining

with

milling

-300

broaching

cost

reaming

boring, turning

in

barrel finishing

-200

increase

electrolytic grinding

roller burnishing

grinding

%

honing

-100

polishing

lapping

superfinishing

Average usage of operation

less common usage

• A table of roughness measurements is given below [Krar],