- Standards : ASME B46.1
- RA Formula: Ra = (1/L) * ∫ |Z(x)| dx
- RMS Formula: RMS = √((1/L) * ∫ Z(x)² dx)
Understand Difference Between RMS vs Ra
RMS vs Ra Comparision
RMS
- Root Mean Square
- Use : General manufacturing
Ra
- Roughness Average
- Use : Aerospace
Must Know Surface Roughness vs Surface Finish
Surface Roughness vs Surface Finish
Surface Roughness
- Measured using specific instruments
- Parameters :Ra, Rq
Surface Finish
- based on roughness value
- Parameters : Roughness
Find Ra Roughness Chart and Different Method of Measuring Roughness
Ra Roughness Chart
| Roughness Average Ra | |
|---|---|
| μm | μin |
| 3.2-25 | 128-1000 |
| 12.5-25 | 500-1000 |
| 0.8-35 | 32-1000 |
| 1.6-6.3 | 64-250 |
| 3.2-12.5 | 128-500 |
| 0.8-6.3 | 32-250 |
| 0.8-3.2 | 32-128 |
| 0.4-6.3 | 16-250 |
| 0.8-1.6 | 32-64 |
| 0.1-0.4 | 4-16 |
| 0.4-1.6 | 16-64 |
| 0.1-0.8 | 4-32 |
| 0.025-0.4 | 1-16 |
| 0.05-0.4 | 2-16 |
How to Measure Surface Roughness?
- Contact profilometer
- Non-contact profilometer
- Portable surface roughness tester
- Surface roughness comparator
Check Surface Roughness Conversion Chart and Calculator Here
Surface Roughness Conversion Chart
| Ra (Micro-meters) | Rt** | Ra (Micro-inches) | N |
|---|---|---|---|
| 0.05 | 0.5 | 2 | N2 |
| 0.025 | 0.3 | 1 | N1 |
| 0.1 | 0.8 | 4 | N3 |
| 0.4 | 2 | 16 | N5 |
| 0.2 | 1.2 | 8 | N4 |
| 0.8 | 4 | 32 | N6 |
| 3.2 | 13 | 125 | N8 |
| 1.6 | 8 | 63 | N7 |
| 6.3 | 25 | 250 | N9 |
| 25 | 100 | 1000 | N11 |
| 12.5 | 50 | 500 | N10 |
| 50 | 200 | 2000 | N12 |
Turning Surface Roughness Calculator
|
Surface Roughness Chart
See Grit Vs Ra Chart Here
Grit Vs RA Chart
| Grit Finish | RMS (Micron) | RMS (Micro-inch) | Ra (Micron) | Ra (Micro-inch) |
|---|---|---|---|---|
| 36 | 4.06 | 160 | 3.61 | 142 |
| 80 | 2.03 | 80 | 1.8 | 71 |
| 60 | 2.49 | 98 | 2.21 | 87 |
| 150 | 1.2 | 47 | 1.06 | 42 |
| 120 | 1.47 | 58 | 1.32 | 52 |
| 220 | 0.53 | 21 | 0.48 | 19 |
| 180 | 0.86 | 34 | 0.76 | 30 |
| 320 | 0.36 | 14 | 0.3 | 12 |
| 240 | 0.43 | 17 | 0.38 | 15 |
| 400 | 0.25 | 10 | 0.23 | 9 |
| Mirror | 0.13 | 5 | 0.1 | 4 |
Types of Machining Finishes
- As-Machined Finish
- Smooth Finish
- Textured Finish
- Mirror Finish
- Anodised Finish
Surface Roughness Symbol And Meaning
| Symbol | Meaning |
|---|---|
|
Basic Surface Texture Symbol |
|
Material Removal Required |
|
Material Removel Prohibited |
|
|
Surface Texture Symobel |
How To Choose the Most Suitable CNC Machining Surface Roughness?
- Functionality and Purpose
- Cost and Lead Time
- Aesthetics
- Material Properties
- Part Geometry
Ra Surface Finish Grade Numbers Equivalent Ra values
| Roughness N ISO Grade Numbers | Roughness values Ra microinches (μin.) | Roughness values Ra micrometers (μm) | CLA (μin.) Center Line Avg. | RMS | Rt Roughness, microns |
|---|---|---|---|---|---|
| N11 | 1000 | 25 | 1000 | 1100 | 100 |
| N12 | 2000 | 50 | 2000 | 2200 | 200 |
| N9 | 250 | 6.3 | 250 | 275 | 25 |
| N10 | 500 | 12.5 | 500 | 550 | 50 |
| N7 | 63 | 1.6 | 63 | 64.3 | 8.0 |
| N8 | 125 | 3.2 | 125 | 137.5 | 13 |
| N5 | 16 | 0.4 | 16 | 17.6 | 2.0 |
| N6 | 32 | 0.8 | 32 | 32.5 | 4.0 |
| N4 | 8 | 0.2 | 8 | 8.8 | 1.2 |
| N2 | 2 | 0.05 | 2 | 2.2 | 0.5 |
| N3 | 4 | 0.1 | 4 | 4.4 | 0.8 |
| N1 | 1 | 0.025 | 1 | 1.1 | 0.3 |
Surface Finish Measurements
RMS Roughness Calculation
- RMS = SQRT[ 1/n* SUM(Zi-Zmean)^2 ] from i=1 to n
- Measure height across the microscopic peaks and valleys
- Calculate the SQUARE of each value
- Calculate the MEAN
- Find the square ROOT
Ra value For Different Material
| Material | RA Value |
|---|---|
| Steel | 0.2 µm to 3 µm |
| Aluminum | 0.1 µm to 1 µm |
| Copper | 0.1 µm to 1 µm |
| Titanium | 0.5 µm to 4 µm |
What Is Significance Of Ra And RMS In Industry?
- material selection
- Choosing processing techniques
- Can Improve durability
- functionality
- enhancing performance
Surface Roughness Abbreviation
| Abbreaviations | Meaning |
|---|---|
| Ra | Average Surface Roughness |
| Rmax | Vertical Distance from Peak to Valley |
| Rz | Average Maximum Height of the Profile |
What Are the Factors Affecting Surface Finish?
- Machine tool condition
- Feeds and speeds
- Cut width
- Vibration
- Tool deflection
- Coolant
Average Roughness Value Of Different Machining Process
| Machining Processes | Roughness Average Range | |||||
|---|---|---|---|---|---|---|
| Max. | Min. | Max. | Min. | Max. | Min. | |
| RA(μm) | RA(μm) | RMS(μm) | RMS(μm) | CLA(μin) | CLA(μin) | |
| Flame Cutting | 25 | 12.5 | 27.5 | 13.75 | 1000 | 500 |
| Sawing | 25 | 1.6 | 27.5 | 1.76 | 1000 | 63 |
| Drilling | 6.3 | 1.6 | 6.93 | 1.76 | 250 | 63 |
| EDM Machining | 0.4 | 0.1 | 0.44 | 0.11 | 250 | 63 |
| Broaching | 3.2 | 0.8 | 3.52 | 0.88 | 125 | 32 |
| Electron Beam | 6.3 | 0.8 | 6.93 | 0.88 | 250 | 32 |
| Electro-Chemical | 3.2 | 0.2 | 3.52 | 0.22 | 125 | 8 |
| Barrel Finishing | 0.8 | 0.2 | 0.88 | 0.22 | 32 | 8 |
| Roller Burnishing | 0.4 | 0.2 | 0.44 | 0.22 | 16 | 8 |
| Honing | 0.8 | 0.1 | 0.88 | 0.11 | 32 | 4 |
| Polishing | 0.4 | 0.1 | 0.44 | 0.11 | 16 | 4 |
| Super Finishing | 0.2 | 0.025 | 0.22 | 0.0275 | 8 | 1 |
| Hot Rolling | 25 | 12.5 | 27.5 | 13.75 | 1000 | 500 |
| Perm. Mold Casting | 3.2 | 1.6 | 3.52 | 1.76 | 125 | 64 |
| Cold Rolling, Drawing | 3.2 | 0.8 | 3.52 | 0.88 | 125 | 32 |
CNC Machining Achievable Surface Roughness
- 1.6 μm Ra
- 3.2 μm Ra
- 0.4 μm Ra
- 0.8 μm Ra