cditorque.com


Search:

What is Torque?

According to Webster:

A twisting or wrenching effect, or moment, exerted by a force acting at a distance on a body, equal to the force multiplied by the perpendicular distance between the line of action of the force, and the center of rotation at which it is exerted.
A force, which tends to produce rotation. The measurement of torque is based on the fundamental law of the lever.

Basic Torque Formula
L (length) x F (force) = T (torque)

Example: A two foot lever at a right angle to the fastener with 200 pounds at the end will produce
400 foot/pounds of torque.

Torque Formula: L x F = T

What are we trying to achieve with a torque wrench?

Answer: Proper Clamping Force

Torque is expressed in commonly used units of measurement such as:
in. lbs. = inch pounds
in. ozs. = inch ounces
ft. lbs. = foot pounds
Nm = Newton meter
cNm = Centi Newton meter

Torque and Clamping Force
Controlling the torque applied in tightening threaded fasteners is the most commonly used method for the application of clamping force. There are many factors which may affect the relationship between torque and clamping force of threaded fasteners. Some of these are: the type of lubricant used on the threads, the material from which the bolt and nut are made, the type of washers used, the class and finish of threads and various other factors. It is not possible to establish a definite relationship between torque and clamping force which will be applicable for all conditions.

Torque Versus Clamping Force

Only a small part of the torque applied to a fastener contributes to clamping force. The remaining, as much as 90% of the total applied torque, is used to overcome friction under the fastener head (or between nut and washer) and friction in thread engagement.

TORQUE

Head Friction:
45% - 55%

Thread Friction:
35% - 45%

Clamping Force:
10%

TORQUE

1. Head Friction
2. Thread Friction
3. Clamping Force

> return to top

Torque Wrench Safety

These precautions should always be taken when using any torque wrench to avoid possible injury:

Read instruction manual completely before using torque wrench.
Safety glasses or goggles should be worn at all times when using any hand tool.
Always pull, DO NOT PUSH, to apply torque and adjust your stance to prevent a fall.
A "cheater bar" should NEVER be used on a torque wrench to apply excess leverage.
Do not use with sockets or fasteners showing wear or cracks.
Ratchet mechanism may slip or break if dirty, mismatched or worn parts are used.
Make sure direction lever is fully engaged.

All mechanical torque wrenches are calibrated from 20% to 100% of full scale, therefore, they should never be used below or above those limits
To determine which torque wrench capacity is best suited for an application, many factors must be considered. However, as a recommendation, use a torque wrench in the middle 50% of the overall capacity of the tool. This will result in longer tool life, ease of use for the operator and increased accuracy from "clicker" type torque wrenches
Always grasp handle firmly in the center of the grip
Approach final torque slowly and evenly
Stop pulling wrench immediately when target torque is reached
Never use a torque wrench to break fasteners loose
Should be cleaned and stored properly
Should always be stored at it’s lowest torque setting
Wrenches should be re-calibrated if dropped. Should never be used in excess of it’s capacity
Torque wrenches should be "exercised" a minimum of three times at 100% of full scale before use
The wrench selected should be calibrated in the same torque units that are specified
Use of a "cheater bar" will result in an inaccurate reading and can possibly damage the wrench
Torque wrenches will last longer if reasonable care is taken. Always unwind handle to the lowest setting after each use. Do not attempt to lubricate the internal torque mechanism. Clean torque wrench by wiping, do not immerse. The wrench should be sent to a qualified calibration lab once every year or every 5000 cycles for re-calibration

> return to top

Torque Conversion

Easy-to-use Torque
Conversion Table

To Convert From	To	Multiply by
in. oz.	in. lb.	0.0625
in. lb.	in.oz.	16
in. lb.	ft.lb.	0.08333
in. lb.	cmkg	1.1519
in. lb.	mkg	0.011519
in. lb.	Nm	0.113
in. lb.	dNm	1.13
ft. lb.	in. lb.	12
ft. lb.	mkg	0.1382
ft. lb.	Nm	1.356
dNm	in. lb.	0.885
dNm	Nm	0.10
Nm	dNm	10
Nm	cmkg	10.2
Nm	mkg	0.102
Nm	in. lb.	8.85
Nm	ft. lb.	0.7376
cmkg	in. lb.	0.8681
cmkg	Nm	0.09807
mkg	in. lb.	86.81
mkg	ft. lb.	7.236
mkg	Nm	9.807

Common Torque Abbreviations

Foot Pounds – ft. lbs.
Inch Pounds – in. lbs.
Inch Ounces – in. ozs.
Newton Meter – Nm
Centi-Newton Meter – cNm
Meter Kilogram – Mkg

Torque Conversion Calculators

To convert torque values for other units, click on the unit you are starting with below and a popup window calculator will provide you a quick way to make the conversions:

Use of Adapter

Formula:

TA x L
L + A

= TW

Length (L) =

Effective length of the wrench as described below.

Dial Wrenches =

The measured distance from the center of the square drive to the center ring or notch on the handle.

Micrometer Wrenches =

The measured length from the center of the square drive to the center of the handle, with the wrench set at the desired torque reading.

Desired Torque (TA) =

The torque value designated for the fastener with or without an adapter.

Added Length of Adapter (A) =

The measured length from the center of the adapter drive to the center of the wrench square drive.

New Setting (TW) =

The torque setting on the wrench allowing for the added length of the adapter. This reading will be lower than the desired torque.

Example:

250 ft. lb. Dial Wrench using a 2” long crowfoot adapter

L = Effective Length: 18.75”
Desired Torque = 250 ft. lb.
Length of Adapter = 2”

Result:

18.75" x 250 ft. lb.
18.75" + 2"

= Pull Wrench to 226 ft. lb.

> return to top

Indicated Value vs. Full Value

Issues to consider when selecting an electronic torque tester:

1 Accuracy: Generally there are two ways of stating accuracy:

A. % of full-scale deflection or FSD
B. % of indicated value or reading

The following example will show the difference between the two methods:

Case 1 - Assume you have a 100 ft. lb. tester (maximum), and that the stated accuracy is +/- 0.5% of full scale.

At 100 ft. lb. +/- 0.5% full scale error = .5 ft, lb. This represents the “best case” error of the system. However, when a lower range is utilized, this .5 ft-lb becomes more significant. That is, on the same 100 ft. lb. tester;

      at 50 ft. lb. - .5 ft. lb. error = 1% accuracy
      at 10 ft, lb. - .5 ft. lb. error = 5% accuracy
      at 1 ft. lb. - .5 ft. lb. error = 50% accuracy

Therefore, what looks to be a good accuracy reading at full-scale actually translates into substantial error at the low range of the tester.

Case 2 - Assume you have a 100 ft. lb. tester (maximum), and that the stated accuracy is +/- 0.5% of indicated value.

      at 100 ft. lb. - .5% error .5 ft. lb.
      at 50 ft. lb. - .5 % error .25 ft. lb.
      at 10 ft. lb. - .5% error .05 ft. lb.

As can be seen by the above examples, error as related to full-scale value increases significantly as you go lower in the range, while error as related to indicated value stays constant throughout the useful range of the tester.

2 Range: Generally when manufacturers advertise % error of full-scale, their useful ranges will be advertised from zero to full-scale. That is, +/- 0.5% accurate (full-scale) from 0-100 ft. lb. This is interesting because at zero ft. lb., the system is only accurate to within +/- 0.5 ft. lb. Basically, error goes to infinity at zero.

Furthermore, transducers which are used to convert the mechanical torque into an electrical signal may become inconsistent below 10% of full-scale deflection.

It is for the above stated reason that systems which have accuracy as related to indicated value should state the useful range to be 10% to 100% of the tester range.

Therefore, if a tester has 100 ft. lb. maximum range, it should not be used at less than 10 ft. lbs. if the desired accuracy is needed.

It is CDI’s belief that in order to be completely honest to the customer, accuracy should always be stated as a percent of indicated value and the useful range should correspond to that stated accuracy. This will prevent the user from having to calculate what the
real error is at any given range.

3 Circuitry: There are two basic ways of measuring the output of a torque transducer.

Analog (non-microprocessor based pure analog)
Digital (microprocessor based plus analog input)

Without in-depth explanations of these two systems, the following advantages of having digital circuitry are well known throughout the electronics industry.

Digital systems are economical, flexible and compact.
Digital systems improve reliability in the face of hardware imperfections.
Digital systems allow the ability to make logical decisions, carry out digital computations (unlimited unit conversion) and store the results in memory.

Basically, full digital systems are computer controlled. It is important that the terms “digital display” or “digital memory” do not necessarily mean that the system has full digital circuitry.

> return to top

Bolt Torque Specifications

Bolt Torque Charts
These charts show suggested maximum torque values for threaded products and are intended only as a guide. Always refer to the manufacturers recommended torque values if possible. CDI Torque Products is not responsible for any application of torque or it's consequences as a result of using this chart. Use at your own risk!

Bolt Size	18-8 Stainless Steel	Brass	Aluminum 2024-T4	316 Stainless Steel	Nylon
INCH POUNDS
2 - 56	2.5	2.0	1.4	2.6	0.44
4 - 40	5.2	4.3	2.9	5.5	1.19
4 - 48	6.6	5.4	3.6	6.9
6 - 32	9.6	7.9	5.3	10.1	2.14
6 - 40	12.1	9.9	6.6	12.7
8 - 32	19.8	16.2	10.8	20.7	4.30
8 - 36	22.0	18.0	12.0	23.0
10 - 24	22.8	18.6	13.8	23.8	6.61
10 - 32	31.7	25.9	19.2	33.1	8.20
1/4" - 20	75.2	61.5	45.6	78.8	16.00
1/4" - 28	94.0	77.0	57.0	99.0	20.80
5/16" - 18	132.0	107.0	80.0	138.0	34.90
5/16" - 24	142.0	116.0	86.0	147.0
3/8" - 16	236.0	192.0	143.0	247.0
3-8" - 24	259.0	212.0	157.0	271.0
7/16" - 14	376.0	317.0	228.0	393.0
7/16" - 20	400.0	357.0	242.0	418.0
1/2" - 13	517.0	422.0	313.0	542.0
1/2" - 20	541.0	443.0	328.0	565.0
9/16" - 12	682.0	558.0	413.0	713.0
9/16" - 18	752.0	615.0	456.0	787.0
5/8" - 11	1110.0	907.0	715.0	1160.0
5/8" - 18	1244.0	1016.0	798.0	1301.0
3/4" - 10	1530.0	1249.0	980.0	1582.0
3/4" - 16	1490.0	1220.0	958.0	1558.0
7/8" - 9	2328.0	1905.0	1495.0	2430.0
7/8" - 14	2318.0	1895.0	1490.0	2420.0
1" - 8	3440.0	2815.0	2205.0	3595.0
1"- 14	3110.0	2545.0	1995.0	3250.0

Bolt Size Inches	Coarse Thread/ inch	SAE 0-1-2 74,000 psi Low Carbon Steel	SAE Grade 3 100,000 psi Med Carbon Steel	SAE Grade 5 120,000 psi Med. Carbon Heat T. Steel	SAE Grade 6 133,000 psi Med. Carbon Temp. Steel	SAE Grade 7 133,000 psi Med. Carbon Alloy Steel	SAE Grade 8 150,000 psi Med Carbon Alloy Steel
FOOT POUNDS
1/4	20	6	9	10	12.5	13	14
5/16	18	12	17	19	24	25	29
3/8	16	20	30	33	43	44	47
7/16	14	32	47	54	69	71	78
1/2	13	47	69	78	106	110	119
9/16	12	69	103	114	150	154	169
5/8	11	96	145	154	209	215	230
3/4	10	155	234	257	350	360	380
7/8	9	206	372	382	550	570	600
1	8	310	551	587	825	840	700
1-1/8	7	480	872	794	1304	1325	1430
1-1/4	7	375	1211	1105	1815	1825	1975
1-3/8	6	900	1624	1500	2434	2500	2650
1-1/2	6	1100	1943	1775	2913	3000	3200
1-5/8	5.5	1470	2660	2425	3985	4000	4400
1-3/4	5	1900	3463	3150	5189	5300	5650
1-7/8	5	2360	4695	4200	6980	7000	7600
2	4.5	2750	5427	4550	7491	7500	8200

> return to top