Mechanical Engineering Standards

Bolt

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Bolt, commonly used with nuts, are the most widely used non-permanent fastening. The bolt head is usually hexagonal but may be square or round. The shank is screwed with a vee thread for all or parts of its length.

Materials

Most bolts are made of low or medium carbon steel by forging or machining and the threads are formed by cutting or rolling. Forged bolts are called black and machined bolts are called bright. They are also made in high tensile (HT bolts 8.8), alloy steel, stainless steel, brass and other metals.

TYPES OF BOLTS

1. Machine Bolt 4. Stove Bolt

2. Eye Bolt 5. U bolt

3. Stud Bolt 6. Carriage Bolt

TYPES OF SCREWS

1. Cap Screw

2. Machine Screw

3. Set Screw

4. Power Screw

THE AMERICAN NATIONAL SCREW THREAD

TYPES OF THREADS-

1. UNC (Unified National Coarse Series) – is recommended for general use, where jar and vibration are not important factors, where dis-assembly of parts is frequent, and where tapped holes are in metals other than steel.

2. UNF (Unified National Fine Series) – is frequently used in automotive and aircraft work especially where jar and vibration (tending to loosen the nut) are present, where a fine adjustment is required with the use of a castle nut, and where a fine adjustment is required with the use of castle nut, and where tapped holes are in steel (avoid UNF in brittle materials)

3. UNEF (Unified National Extra Fine) – is particularly useful in aeronautical equipment, suitable where thin-walled materials is to be threaded, where fine adjustment are required, and where jar and vibration are excessive. Screws with these threads are likely to be made of heat treated alloy steel.

4. 8UN (Unified 8 – thread series) – is used on bolt for high-pressure pipe flanges, cylinder-head studs, etc. These are several constant pitch series, the 12 UN, 16 UN, and 20 UN. These threads are useful because in the regular coarse thread, the pitches continue to increase with size and it becomes increasingly difficult to induce the desire initial tension in the bolt, so necessary for tight joint. Even for the 8 UN thread, impact wrenches or very large leverages are needed for tightening to stresses of the order of the yield strengths.

EXTRA FINE 8-THREAD SERIES TABLE

EXTRA FINE SERIES (NEF AND UNEF)					8-THREAD SERIES (8 N and 8 UN) (Primary Sizes)
Size	Basic Major Diameter, in.	Th./In. (tpi)	Minor Dia. Ext Th.	Stress Area A_S sq. in.	Size	Minor Dia. Ext. Th.	Stress Area A_s sq. in
12	0.2160	32	0.1777	0.0270	1	0.8466	0.606
1/4	0.2500	32	0.2117	0.0379	1 1/8	0.9716	0.790
5/16	0.3125	32	0.2742	0.0625	1 ¼	1.0966	1.000
3/8	0.3750	32	0.3367	0.0932	1 3/8	1.2216	1.233
7/16	0.4375	28	0.3937	0.1274	1 1/2	1.3466	1.492
1/2	0.5000	28	0.4562	0.170	1 5/8	1.4716	1.78
9/16	0.5625	24	0.5114	0.214	1 3/4	1.5966	2.08
5/8	0.6250	24	0.5739	0.268	1 7/8	1.7216	2.41
11/16	0.6875	24	0.6364	0.329	2	1.8466	2.77
3/4	0.7500	20	0.6887	0.386	2 1/4	2.0966	3.56
13/16	0.8125	20	0.7512	0.458	2 1/2	2.3466	4.44
7/8	0.8750	20	0.8137	0.536	2 3/4	2.5966	5.43
15/16	0.9375	20	0.8762	0.620	3	2.8466	6.51
1	1.0000	20	0.9387	0.711	3 1/4	3.0966	7.6738
1 1/16	1.0625	18	0.9943	0.799	3 1/2	3.3466	8.96
1 1/8	1.1250	18	1.0568	0.901	3 3/4	3.5966	10.34
1 3/16	1.1875	18	1.1193	1.009	4	3.8466	11.81
1 1/4	1.2500	18	1.1818	1.123	4 1/4	4.0966	11.38
1 5/16	1.3125	18	1.2443	1.244	4 1/2	4.3466	15.1
1 3/8	1.3750	18	1.3068	1.370	4 3/4	4.5966	16.8
1 7/16	1.4375	18	1.3693	1.503	5	4.8466	18.7
1 1/2	1.5000	18	1.4318	1.64	5 1/4	5.0966	20.7
1 9/16	1.5625	18	1.4943	1.79	5 1/2	5.3466	22.7
1 5/8	1.6250	18	1.5568	1.94	5 3/4	5.5966	24.9
1 11/16	1.6875	18	1.6193	2.10	6	5.8466	27.1

HEX HEAD BOLT STANDARD DIMENSION (by American Society Of Mechanical Engineering)

Bolt Diameter	Body Diameter Max Min		Across Flat	Across Corner Max Min		Height of Bolt	Length Tread 6 in. below	Length Tread 6 in. Above
¼	0.26	.237	7/16	.505	.484	11/64	.75	1.0
5/16	.324	.298	½	.577	.522	7/32	.88	1.13
3/8	.388	.360	9/16	.650	.62	¼	1.0	1.25
7/16	.452	.421	5/8	.722	.687	19/64	1.13	1.38
½	.515	.482	¾	.866	.826	11/32	1.25	1.50
5/8	.642	.605	15/16	1.083	1.033	27/64	1.50	1.75
¾	.768	.729	1 1/8	1.299	1.24	½	1.75	2.00
7/8	.895	.852	1 5/16	1.516	1.447	37.64	2.0	2.25
1	1.022	.976	1 ½	1.732	1.653	43/64	2.25	2.50
1 1/8	1.149	1.098	1 11/16	1.949	1.859	¾	2.50	2.75
1 ¼	1.277	1.223	1 7/8	2.165	2.066	27/32	2.75	3.00
1 3/8	1.404	1.345	2 1/16	1.949	1.859	29/32	3.00	3.25
1 ½	1.531	1.47	2 ¼	2.598	2.48	1	3.25	3.50
1 ¾	1.785	1.716	2 5/8	3.031	2.893	1 5/32	3.75	4.00
2	2.039	1.964	3	3.164	3.306	1 11/32	4.25	4.50
2 ¼	2.305	2.212	3 3/8	3.897	3.719	1 ½	4.75	5.00
2 ½	2.559	2.461	3 ¾	4.33	4.133	1 21/32	5.25	5.50
2 ¾	2.827	2.711	4 1/8	4.763	4.546	1 13/16	5.75	6.00
3	3.081	2.961	4 ½	5.196	4.959	2	6.25	6.50
3 ¼	3.335	3.21	4 7/8	5.629	5.372	2 3/16	6.75	7.0
3 ½	3.589	3.461	5 ¼	6.062	5.786	2 5/16	7.25	7.50
3 ¾	3.858	3.726	5 5/8	6.495	6.198	2 ½	7.75	8.00
4	4.111	3.975	6	6.928	6.612	2 11/16	8.25	8.50

Rivets

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Rivets are made of wrought iron or soft steel. It is used as fastener for joints in building, bridges, boilers, tanks, ships, and miscellaneous framework.

Types of Riveted Joints

1. Lap Joints

a. A single riveted lap joint

b. Double riveted lap joint

c. Triple riveted lap joint

2. Butt Joint

a. Single riveted butt joint

b. Double riveted butt joint

c. Triple riveted butt joint

Common Assumptions

1. The load is distributed among the rivets according to the shear areas.

2. There is no bending stress in the rivets.

3. The tensile stress is equally distributed over the projected area of the rivets.

4. In a rivet subjected to double shear, the shear is equally distributed area of the rivet.

5. The crushing pressure is equally distributed over projected area of of the rivet.

6. The holes into which the rivets are given so not weaken the member if it is in compression.

7. After they have been driven, the rivet completely fills the holes.

8. Friction between adjacent surfaces does not affect the strength of the joints.

For riveted Joints

1. Tangential Design Stress

S_t = P_iD_i

2 t e

Where:

S_t = tangential Stress , Mpa or psi

P_i = inside pressure, Mpa or psi

D_i = inside diameter, mm or in.

t = wall thickness, mm or in.

e = efficiency

2. Factor of Safety

FS = S_tu/ S_t

Where:

S_t = tangential Stress , Mpa or psi

S_{tu =}ultimate tensile, Mpa or psi

FS = factor of safety

3. Efficiency of the joint for single riveted but joint

e = p – d X 100

Where:

p = pitch, mm or in.

d = rivet diameter, mm or in.

e = efficiency

Gear

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GEARS - are toothed cylindrical wheels used in transmitting motion and power from one rotating shaft to another.

Classification of Gears According to the Nature of Axis

1. Parallel Axis

a. External Spur Gear d. Herringbone Gear

b. Internal Spur Gear e. Rack & Pinion

c. Twisted Spur Gear f. Pin Gearing

2. Intersecting Axis

a. Plain Bevel Gear

b. Crown Bevel Gear

c. Spiral Bevel Gear

3. Non- intersecting or Non-Parallel Axis

a. Hyperboloidal

b. Hypoid

c. Screw Gear

Kinds Of Gears

1. Spur Gear 3. Worm Gear

2. Helical Gear 4. Bevel Gear

1. Spur Gear – are gear having teeth that are straight and arranged parallel to the axis of the shaft carries the gear. The curve shapes of the faces of the spur gear teeth have a special geometry called involute curve.

Spur Gear Formulas:

1. Circular Pitch

P_c = π D_PP_c = π D_g P_c = π M

N_P N_g

Where:

P_c = circular pitch, mm/tooth or in/tooth

M = module, mm/tooth or in/tooth

P_d = diameter pitch, mm or in.

D_g = Gear diameter, mm or in.

D_p = pinion diameter, mm or in.

N_g = Number of teeth in gear

N_p = number of teeth in pinion

2. Diameter Pitch

P_d= N_p/ D_pP_d= N_g / D_g P_d = π/P_cP_d = 1 / M

Where:

P_c = circular pitch, mm/tooth or in/tooth

M = module, mm/tooth or in/tooth

P_d = diameter pitch, mm or in.

D_g = Gear diameter, mm or in.

D_p = pinion diameter, mm or in.

N_g = Number of teeth in gear

N_p = number of teeth in pinion

3. Clearance

C = d – a C = W - W_r

Where:

a = addendum, mm or in.

P_d = diametral pitch, tooth/mm or tooth/in

W = whole depth, mm or in.

W_r = working depth, mm or in.

4. Addendum

a = 1 / P_d

Where:

a = addendum, mm or in.

P_d = diametral pitch, tooth/mm or tooth/in

5. Dedendum

a. For 14 1/2° and 22 1/2°

d = 1.157 / P_d

b. For 20° and 25°

d = 1.25 / P_d

Where:

a = addendum, mm or in.

P_d = diametral pitch, tooth/mm or tooth/in

6. Outside Diameter

a. For Pinion

D_op = D_p+ 2_a = (N_p + 2) / P_d

b. For Gear

D_og = N_p + 2 = D_g + 2_a

P_d

Where:

P_d = diametral pitch, tooth/mm or tooth/in

D_g = Gear diameter, mm or in.

D_p = pinion diameter, mm or in.

N_p = number of teeth in pinion

D_op = outside diameter of pinion, mm or in

7. Root Diameter

a. For Pinion

D_rp = D_p– 2_a

b. For Gear

D_rg = D_g – 2d

Where:

D_g = Gear diameter, mm or in.

D_p = pinion diameter, mm or in.

D_rp = root diameter of pinion, mm or in.

D_rp = root diameter of pinion, mm or in

d = dedendum

8. Whole depth

W = a + d W = W_r + C

Where:

W = whole depth, mm or in.

c = clearance, mm or in.

W_r = working depth, mm or in.

a = addendum, mm or in.

d = dedendum, mm or in.

9. Working Depth

W_r= 2a W_r = W - C

Where:

W = whole depth, mm or in.

W_r = working depth, mm or in.

a = addendum, mm or in.

d = dedendum, mm or in.

10. Tooth Thickness

a. For Backlash is zero

T = P_C/ 2

b. For Backlash is not zero

T = P_C - B

Where:

T = tooth thickness, mm/ tooth or in/tooth

P_c = circular pitch, mm/tooth or in/tooth

B = backlash, mm or in.

11. Tooth Space

S = T + B

Where:

T = tooth thickness, mm/ tooth or in/tooth

B = backlash, mm or in.

S = tooth space or space width, mm or in.

12. Base Circle Diameter

a. For Pinion

D_bp = D_pcosф

b. For Gear

D_bg = D_gcosф

Where:

D_g = gear diameter, mm or in.

D_p = pinion diameter, mm or in.

D_bp = base circle diameter of pinion, mm or in.

D_bg = base circle diameter of gear, mm or in.

Ф = pressure angle, deg

13. Center distance between gear

C = (D_g + D_p) / 2 --- for external contact

C = (D_g - D_p) / 2 --- for internal contact

Where:

C = center distance between gears, mm or in.

D_g = gear diameter, mm or in.

D_p = pinion diameter, mm or in.

14. Backlash

B = S – T

B = 0.03 to 0.04

P_dp_d
Where:

T = tooth thickness, in./tooth

B = backlash, in

S = tooth space or space width, in.

Pd = diametral pitch, or tooth/in.

15. Face Width

2.5P_c < b > 4 P_c

(8 / P) < b > (12.5 / Pd)

Where:

b = face width

Pd = diameter pitch

Pc = circular pitch

SPUR GEAR applications:

2. Helical Gear are gears arranged so that they lie at an angle with respect to the axis of the shaft.

Formulas (Helical Gears)

1. Tangential Force

F_t = F_r

tanф

Where:

F_t = tangential force, N or lb.

F_r = radial force, N or lb.

Ф = pressure angle, deg

2. Radial Force

F_r = F_n sin ф

Where:

F_n = normal force, N or lb.

F_r = radial force, N or lb.

Ф = pressure angle, deg

3. Axial Force

F_a= F_t tan δ

Where:

F_a = axil force, N or lb.

F_t= tangential force, N or lb.

δ = helix angle, deg
4. Normal Pressure Angle

Ф_n = tan ^-1(tan ф cos δ)

Where:

Ф = pressure angle, deg

Ф_n = normal pressure angle, deg.

δ = helix angle, deg

5. Axial Pitch

P_a = P_cn / tan _δ or π / P_dtan_δ

Where:

P_a = axial pitch

P_cn = normal circular pitch

P_d = diametral pitch

δ = helix angle, deg

6. Normal Diametral Pitch

P_dn = P_d / cos δ

Where:

P_dn = normal diametral pitch

P_d = diametral pitch

δ = helix angle, deg

7. Normal Circular Pitch

P_cn = P_c cos δ

Where:

P_cn = normal circular pitch

P_c = circular pitch

δ = helix angle, deg

Helical Gear Applications:

Coupling

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Coupling – is a mechanical device for connecting parts of mechanical equipment's.

Main Type of Couplings

1. Rigid Coupling

2. Flexible Coupling

1. Types of Rigid Coupling

a. Flange Coupling

b. Collar Coupling

2. Types of Flexible Coupling

a. Chain Coupling

b. Flexible Disk Coupling

c. Oldham Coupling

d. Gear Coupling

e. Hydraulic Coupling

f. Universal Coupling

Tips in Designing Coupling

1. Calculation of coupling design is base on the assumption that shaft are perfectly or accurately aligned so that bending loads are negligible. Therefore, coupling problem are analyzed for torsion only.

2. The safe power which can be transmitted by the flange coupling are computed base on the following:

a. Shearing of the key

b. Compressive of the key

c. Shearing of the bolt between the flange faces

d. Compression between the bolts and the flange

Calculation of the Safe Torque that gives safe Power Transmitted

1. Based on the shearing of the Key

T= S_sDWL

Where:

S_s = shearing stress, Mpa or psi

D = diameter of the shaft, mm or in

w = length of the key, mm or in

L= length of the key, mm or in

T = torque, N-m or lb-in

2. Base on compression between key and keyways

T = S_sDHL

Where:

S_c = compressive stress, Mpa or psi

D = diameter of the shaft, mm or in

h = thickness of the key, mm or in

L = length of the key, mm or in

T = torque, N-m or lb-in.

3. Base on shearing of bolts the flange faces

T = F_SD_bc = S_sπD_b²D_bcN_B

2 8

Where:

T = torque, N-m or lb-in.

D_bc= bolt circle diameter, mm or in.

D_b = bolt diameter, mm or in.

N_b = total number of bolts

S_s= shearing stress, Mpa or Psi

F_s = shearing force, N or lb.

4. Based on compression between the bolts and the flange

T = F_cD_bc = S_cπD_b²D_bcN_B

2 8

Where:

T = torque, N-m or lb-in.

D_bc= bolt circle diameter, mm or in.

D_b = bolt diameter, mm or in.

N_b = total number of bolts

S_c= compression stress, Mpa or Psi

F_c= compression force, N or lb.

Power=2πTN
Where:

P= power, kw or hp

T = torque, N-m or lb-in.

N= revolution per minute, rpm or rps.

Coupling application:

Bearing

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Bearing – is machine member which supports guides and control the motion of the others.

Bearing Materials

1. Babbit 4. Bronze

2. Aluminum 5. Porous Metal

3. Plastics

Classification of Bearing According to Type of friction

1. Sliding Bearing

2. Rolling Bearing

Classification of Rolling-Element Bearing

1. Ball Bearing

2. Roller Bearing

3. Needle Bearing

Classification of Bearing According to Load Application

1. Radial Bearing

2. Thrust Bearing

3. Guide Bearing

THE PURPOSE OF BEARING LUBRICATIONS

1. To provide a low-friction film between the rolling elements and the races of the bearing and at point of contact with cages, guiding surfaces, retainers and so on.

2. To protect the bearing component from corrosion.

3. To help dissipate heat from the bearing unit.

4. To carry heat away from the bearing unit.

5. To help dispel contaminants and moisture from the bearing.

FORMULAS

1. Maximum Contact Stress for Balls

S_{smax =}0.31S_max

Where:

S_smax= maximum contact stress, psi

S_max = maximum Herzian Contact stress, psi

2. Maximum Contact Stress for Cylinder

S_{smax =}0.31S_max

Where:

S_smax= maximum contact stress, psi

S_max = maximum Herzian Contact stress, psi

3. Bearing Pressure

P= F/A or F/LD

Where:

P= maximum bearing pressure, Mpa, Psi

F= load, N, or lb

A= across section area, mm², in²

L= length, mm or in.

D= diameter, mm or in.

4. Frictional Torque

Tf= Ff (D/2)

Where:

f= coefficient of friction

N= rotative speed, rpm or rps

W= weight or load, N or lbs

V= velocity, m/s or ft/s

T_f= frictional torque, N-m or lb-in

5. Frictional Power

P_f= 2ΠTN = fwv

Where:

f= coefficient of friction

N= rotative speed, rpm or rps

W= weight or load, N or lbs

V= velocity, m/s or ft/s

T_f= frictional torque, N-m or lb-in

P= frictional power, KW or Hp

6. Life in Millions of Revolutions

a. For Ball Bearing

L₃ = (C/P)³

b. For Roller Bearing

L₁₀=(C/P)^10/3

Where:

C=specific dynamic capacity, lb

P= equivalent load, lb

L₃and L₁₀= life of bearing

7. Life in Hours

a. For Ball Bearing

L₃= 16667 (C/P)³

Rpm

B. For Roller Bearing

L₃= 16667 (C/P)^10/3

Rpm

Where:

C=specific dynamic capacity, lb

P= equivalent load, lb

L₃and L₁₀= life of bearing

Rpm= revolution per minute

8. Compressive Breaking Load

F_c = _k_ (D²⁾

Where:

K= 100, 000 for carbon steel balls

= 125,000 for hardened alloy steel balls

FS = factor of safety

D = ball diameter, in

F_c = compressive breaking load, lb

9. Maximum load

F_max= 4.37 (F)

Where:

n= no of ball

F= total radial load, lb

F_max= maximum load, lb

10. Diameter Clearance

C_d = D-d

Where:

d= journal diameter, mm or in.

D= bearing diameter, mm or in.

C_d= diameter clearance, mm or in.

Sprocket and Roller Chain

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Sprocket and Roller Chain- A mechanical devised that are used in transmitting power from one shaft to another are parallel. It may be single or multi-strand.

General Recommendation in the Design of Chain Drives

1. The minimum number of teeth in a sprocket should 17 unless the drive is operating at a very low speed under 100 rpm.

2. The maximum speed ratio should be 7.0 although higher ratios are feasible. Two or more stages of reduction can be used to achieve higher ratio.

3. The center distance between the sprocket axes should be approximately 30 to 50 inches (30 to 50 times the pitch of the chain).

4. The arc of contact of the chain on the small sprocket should not be smaller than 120®.

5. The larger the sprocket should normally have no more than 120 teeth.

6. The preferred arrangement for a chain drive is with the center line of the sprocket horizon and with the tight side on top.

7. The chain length must be an internal multiple of the pitch and even number of pitches is recommended. The center distance should be made adjustment to accommodate to chain length and to take up tolerance and wear. Excessive sag on slack side should be avoided, especially on drive that are not horizontal.

Type of Sprocket

1. Type A is pain plate

2. Type B has hub on one side only

3. Type C a hub on both side

4. Type D a detachable hub

Type of Lubrication

1. Type I (Manual Lubrication)

2. Type II (Drip Lubrication)

3. Type III (Bath or Disc Lubrication)

4. Type IV (Oil Stream Lubrication)

Recommended SAE viscosities for various operating temperatures:

Temperature Viscosity

20-40°F SAE 20

40-100°F SAE 30

100-120°F SAE 40

120-140°F SAE 50

FORMULAS:

1. Pitch diameter of the small sprocket

D1= p / sin(180/N1)

Where:

P= pitch, mm or in.

N1= number of teeth of the small sprocket

D1= pitch diameter of the small sprocket, mm or in.

2. Pitch diameter of the large sprocket

D2= p / sin(180/N2)

Where:

P= pitch, mm or in.

N1= number of teeth of the small sprocket

D1= pitch diameter of the small sprocket, mm or in.

3. Outside diameter of the small sprocket

OD1= P (0.60+cot(180/N1))

Where:

P= pitch, mm or in.

N1= number of teeth of the small sprocket

OD1= outside diameter of the small sprocket, mm or in.

4. Outside diameter of the large sprocket

OD2= P (0.60+cot(180/N2))

Where:

P= pitch, mm or in.

N2= number of teeth of the large sprocket

OD2= outside diameter of the large sprocket, mm or in.

5. Length of the Chain

L= 2c + ((N1+N2)/2) + ((N2-N1)2/ 40c

Where:

c = center distance between sprockets

N1= number of teeth of the small sprocket

N2= number of teeth of the large sprocket

L= Length of the chain

6. Center Distance between sprockets

C= D1+D2
2

Where:

c = center distance between sprockets

D1 = center distance of small sprocket, mm or in.

D2 = center distance of large sprocket, mm or in.

7. Power Transmitted

P=2πTN

Where:

P= power transmitted, kw or hp

T= torque, N-m or lb-in.

N= linear speed, rpm or rps.

CHAIN AND SPROCKET application.

Fits, Tolerance, Limits & Surface Roughness

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Fits, Tolerance, Limits & Surface Roughness

FIT- is the dimension relationship between mating parts, such as press, shrink or sliding fit.

CLASSES OF FITS

1. Loose Fit 6. Tight Fit

2. Free Fit 7. Medium Fit

3. Medium Fit 8. Medium Force Fit

4. Snug Fit 9. Medium Force Fit

5. Wringing Fit

Loose Fit- it is intended to be used where accuracy is not essential and where consideration freedom is permissible, such as agricultural, mining, and general purpose machinery.

Free Fit- It is suitable for running fits where the speeds are in excess of 600 rpm and the pressure in excess of 600 psi. It is also suitable for shaft of generators, motors, engines and some automotive parts.

Snug Fit- It is a zero allowance fit and is the closest fit than can be assembled by hand.

Wringing Fit- A fit with a slight positive allowance or metal interference and light pressure is required to assemble the parts. It is suitable for semi-permanent assembly for long fits in heavy sections, and for drives in thin section.

Medium Force Fit- A fit that requires considerable force to assemble. It is suitable for press fits on locomotive wheels, car wheel, generator and motor armatures, and crank shafts.

Heavy Force and Shrink Fit- A fit used for steel external member that have a high yield stress.

Tolerance- It is permissible variations in the dimensions of machine parts.

Unilateral Tolerance System- A term applied to a system by which one of the tolerances is zero.

Allowance- it is intentional difference in the basic dimensions of two parts.

Limits- These are the maximum and minimum acceptable dimension of a produced parts.

Lay – It is the predominant direction of the marks visible on the surface.

Flaws- These are irregularities occurring at one or more places on the surface which are not characteristic tics of the surface and cannot be designed by surface, waiveness, or lay

DESCRIPTIONS OF VARIOUS DEGRESS AND SURFACE ROUGNESS

Degree or Roughness Description

2000 rms µin. Unusually rough, low grade surface produced by removing excess stock on heavy work to provide appearances.

1000 rms µin. A very rough surface made by removing stock to nominal dimension.

500 rms µin. A very rough surface made by removing stock of nominal dimension.

250 rms µin. Used as rough finish for soft alloy and for steel, and for hard alloys where moderate notch sensitivity exists but where a rough finish is otherwise tolerable. It is also used on heavy work when good surface contact is essential.

125 rms µin. is the coarse made by removing stock to nominal dimension.

63 rms µin. is used for highly stressed parts that are not subject to serve stress reversals.

32 rms µin. is used for bearing where accuracy is essential where motion is continuous and where loads are light particular if the lay of the surface is I the direction of motion.

16 rms µin. is suitable for close tolerance work, journal bearings, for commercial grade bearing balls and rollers as well as the mating races, the outer diameter of shafts inside such as bearing are housed.

8 rms µin. is used for work to very close tolerances where scratches can not be tolerated. It is suitable for the interior surfaces of hydraulic struts and similar application where properly lubricated seals must slide. It is also suitable for raceways balls and rolls of rolling element bearings when the loads are nominal.

4 rms µin. is suitable for use where packing and rings much slide across the direction of the finish lay such as on buffed chrome-plated piston rods and for hydraulic components. It is also suitable for ball and roller bearings carrying heavy loads.

2 rms µin. is suitable for gages, refrigerator shaft seals. It is expensive to produce.

1 rms µin. is used for micrometer anvils high grades gages, and similar application.