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Selecting theCorrect
Assembly Tool for Fasteners
Using the wrong power tool by the assembler can cause many fasteners to fail. There are several
new types of nut runners and socket drivers on the market that have a wide range of power andtorque output options. Having too much torque can cause unwanted failures.

Hardware & Fastener Components - no.56/2022

Moder n assembly pla nts use t he moresophisticated power tools tha n those used inmaintenance. Most of these tools are digital and will
indicate the sequence and pattern to tighten the bolts
as well as the torque applied. For example, if #2 bolt
is missed in a programmed sequence, the tool will
not allow the #3 fastener to be tightened until the #2
fastener is tightened first. This is a well-designed
progra m of sequence tighteni ng for multiple
fasteners in a connection.

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Automotive assembly lines use these types oftools as well as gang nuts or socket runners. This iswhere several sockets are attached to multiple bolts
in the assembly at the same time, such as head bolts
on an engine or wheel nuts, then slowly torque all
down at the same time. This reduces elastic reboundon critical part assemblies.
Nut runners and powered screw drivers are power
assisted tools driven either by pneumatic or electricalenergy. The nut runners produce low torque thatcan be very accurate. These are used to tighten nuts,flanged head screws and small socket head fasteners
below ½” or 12 mm on sheet metal parts.

///// DC Electric Tools /////
Many earlier nut runners were corded but the DC powered battery tools
are more portable and ergonomically easy to use in tight areas.
The more sophisticated DC electric tools are programmable, store multiple
torque values, have a data base used for error-proofing and some models will
have linear translators for x-y positioning.
The more common and less expensive DC power tools are powered by 20
volt rechargeable Lithium batteries. These tools are mostly used by contractors
and maintenance and the majority of which are not adjustable for output speed.
If the user is not careful, the heads of small screws can easily become twistedoff, such as deck screws and wood screws. If the user is tightening deck screws,etc. with a ½” 20v drill body, there could be many failures.
Comparing the specifications of different well known manufacturers; one ½”
drive 20v power tool has an RPM range of 400-1200-1900 and delivers initial
impacts of 700-1200 lb-ft of torque, another will deliver 600 lb-ft of torque but
only 330 lb-ft initial torque adjustable in pre-set ranges from 0-900-2,000 RPM.
Other models will provide their torque output in inch-pounds, such as 1825
lb-in (152 lb-ft.) or 1400 lb-in (116 lb-ft). There are even ¼” drive 12v models
which produce 1300 lb-in (108 lb-ft) that are very adequate to do the job quickly
and efficiently for smaller fasteners.

Technology >>///// Pneumatic Power Tools /////
Most pneumatic power tools are commonly known as impact wrenches. These are air driven
power tools which produce repeated output blows on an output anvil. The ½” drive models arecommonly used in automotive repair shops, truck shops for glider kit (frame) building and tire
mounting shops. Some larger models are used to tighten large bolts up to 1 ½” (38 mm).
The advantages of pneumatic power tools are their high torque and high speed. A ½”drive medium duty air driver will produce 600 lb-ft of torque at 7,300 RPM with 1,000 beats
per minute (BPM). This is enough torque to destroy any Grade 8 bolt up to 7/8”. The ½” Heavy
Duty model will produce 650 lb-ft of torque at 7,500 RPM with 1,100 BPM. There are someolder models which produce 450 lb-ft of torque.
A ¾” drive air impact wrench will produce 1,000 lb-ft of torque at 6,200 RPM with 750
BPM. On the smaller side, the 3/8” air ratchet will produce 65 lb-ft of torque.
The disadvantage of pneumatic power wrenches is that there are no torque controlson the more common and less expensive models. The output is inaccurate and can change

wh i le i n u s e . T her e a r e mor e
expensive models that can adjust
the output torque. The advantage
is power and speed for larger
fasteners and for removing rusty,
old bolts.
The air supply for these power
tools comes from a generator which
compresses air into a storage tank.
The air is held at a certain pressure,usually around 115-120 pounds-persquare-inch (psi). When the air tool
demands power, the compressor tankdelivers the air at the stored pressure.
The pressure will naturally drop
while being used to a pre-determinedamount, usually around 90 psi, at
which point the compressor starts up
again to regenerate the pressure to120 psi.
It should be noted that tightening
several fasteners at this time will
result in unequal assembly torques.
If another air tool or vehicle lift
is operated at the same time, thepressure drops more rapidly andthe torque disparity is even greater.
Larger shops will probably employ
the industrial heavy duty two-stagecompressor that will keep more of aconstant pressure than the common
single stage shop compressor.

Hardware & Fastener Components - no.56/2022

Torque Wrenches

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Torque wrenches are available intwo categories: manual and torqueangle. The manual wrench is the mostcommon and is available in manystyles: the basic style has a moveable
arm against a scale, some have an
adjustable spring that is calibrated
to dial in a torque value to where thewrench produces a ‘click’ when thevalue has been reached, some have adial gauge that measures and marks
on and off-torque which can be read
after torquing and another type that is
electronic which translates data into
a control module for error-proofing.
Most are low in cost, portable andcan get into tight areas. The accuracy
will range from ± 2-20% depending
on model and cost. Calibration on
the click-type will be lost if dropped;
ot hers may be da maged beyond
normal repair.

Technology >>All manual wrenches depend upon theoperator and installation variables. The
wrench will always ‘see’ 100% of the torque.
It does not detect variations of friction. Theoperator can go fast or slow or vary the speed
between bolts. The operator may switch fromtorquing the nut to torquing the bolt head. Allof these have a direct response to accuracy
and clamp load.
All torque values are to be used as a guide
only. Most are determined of clean and dry
threads or ‘as received’. The only accurate useof any manual torque wrench is when the bolt
threads are lubricated with a known lubricant.

else that needs to be investigated. If none of these anomalies are noticed and theoperator just inputs on torque alone, then there are problems later.

///// Conclusion /////Naturally, if there are complaints of fasteners failing or an assembly failing,check the type of tool used and compressor if it is a pneumatic tool. The bottom
line is, when there becomes a rash of failures on a certain product line, without
any other complaints, always ask how it was installed and what tools wereused. The majority of times it is an operator and equipment error.
Article by Guy Avellon / Copyright owned by Fastener WorldTorque is a function of friction. Friction
can come from debris, burrs, etc. A lubricant
will overcome most types of assembly friction
encountered and produce consistent clamploads.
All engine torque values cited in repair
manuals are considered ‘wet’ torques, yet thehead bolts, connecting rod bolts, etc. do notloosen because the clamp loads are all equaland consistent using the oil as a lubricant.
Products like C5A, Moly-Lube, etc. willaccomplish the same type of consistency andare very accurate. Just be sure the proper
lower torque values are used for the type oflubricant used.

This type of wrench is connected to adata processor which measures the torqueapplied to the rotational angle that the nut orbolt has turned. This is the most accurate
tool used for solid and stiff joints. In mostcases the turn will negate friction variables,
which is why a pre-torque is first applied toestablish a hard base without any further joint
compression.
However, in some cases it will not always
mean that the preload has been achieved.
This depends upon how the data is monitored.
If the torque and angle have been achieved
within a certain percent window, then thejoint is good.
However, if the angle goes significantly
beyond the expected tolerance to achieve theproper torque, this means the joint was not
solid and there was interference between thejoint, such as a burr or even non-conforming
part that produced compression or resistance.
If the torque becomes high and the angle was
not reached, then this could mean debris in
the threads, cross threading or something

Hardware & Fastener Components - no.56/2022

Torque Angle Wrenches

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