Buying power tools of just one type is probably the most common mistake new mechanics make when just starting their careers.
If you are new to the car repair industry and thinking a cupboard full of power tools will make your working life a lot easier.
That’s only true if you have the right tools for the job, because with the right tools you can get things done a lot faster.
But both air and cordless tools have advantages and disadvantages.
For example, if your undoing bolts of an item (perhaps a sump pan of some kind) where the likelihood is, oil will spill everywhere including all over the tool.
Then it’s wise to consider the best kind of tool for the job, i.e. using an air tool covered in oil, certainly won’t hurt it and may arguably be good for it. But covering a cordless tool in oil, well let’s just say it not going to end well with an air-cooled electric motor and circuit boards inside.
In this article, we will explain why you should be selective in your power tool purchases, as well as the advantages and disadvantages of both air and cordless power tools.
Along the way we will also try to do a bit of Myth busting and understand the true meaning of all the various torque values being advertised by manufacturers of impact guns, referring to break away torque, bolt busting torque or ultimate torque.
As mechanics and technicians, we use air or cordless power tools to tighten and loosen bolts and nuts every day without thinking too much about how science or physics prevents threaded fasteners from becoming undone. Nonetheless, on an intuitive level, most of us understand that when we apply an OEM- specified torque of say, 300 Nm to a CV-joint axle nut, the static friction between the threads in the axle and the nut, as well as between the nut and the hub surfaces will prevent the nut from vibrating loose during the normal use of the vehicle.
On a practical level, however, we also know that some nuts and bolts (some Honda crank pulley bolts come to mind) can be particularly stubborn and difficult to undo, so we all want Impact guns that have the power to easily undo stubborn or frozen and seized fasteners. However, it is at this point that things get a little fuzzy and confused with regard to published specifications of some air and cordless tools, so let us look at this aspect of power tool marketing in some detail.
First of all lets delve into all the finer details of how manufacturers of Impact wrenches arrive at the specifications of their products that we see on the packaging. If we go back 20 years (so we are specifically talking air tools now) you find that what was advertised was reasonably accurate and generally repeatable on standard fasteners. The only thing was that the highest torque was always developed in reverse, because the design of an impact guns air motor is biased in the undo direction so that the same gun will always be able to undo a fastener that it did up. In this respect it was always difficult for the customer to verify the max torque performance of an air tool without a torque wrench that would operate in a counter clockwise direction.
However, as time progressed and competition for sales increased amongst the various manufacturers some looked for ways to gain an advantage by advertising the highest possible torque figures they could, without directly telling a lie. This type of marketing is now essentially the worldwide norm as aside from Japan there are no rules or standards in place that define the test protocols for torque outputs regarding impact wrenches.
So, let’s have a look at how they arrive at these figures, firstly the term "breakaway force” refers to the amount of torque an impact wrench must develop to break a threaded fastener loose. The torque required is heavily influenced by the interplays between, clamping force (bolt stretch), ramp action, the pitch of the thread and the surface finish (static friction) between the job and fastener. In the real world it will always take somewhat more torque to undo a fastener, than the torque to which it was done up to. I.e. if a faster is done up to 100Nm it may take 110 ~ 120Nm to undo it, this is largely to do with static friction.
Therefore, if the marketing department of your company wants you to advertise the highest possible figure, but still not tell a lie. Quite simply you need to devise a torque test method which minimises all of the above factors.
To start with you would need a very short and thick bolt (say 32mm dia & 60mm long) with a finely pitched thread, in order to minimise any bolt, stretch and a heavy steel plate to eliminate job compression, we can reduce the static friction by using a polished, hardened steel washer between the job and the fastener, and further reduce friction again by polishing and lubricating the fastener threads themselves.
Now with virtually all of the clamping forces eliminated (no bolt stretch), and friction reduced to a minimum, we then do the fastener up with using a tension wrench to say 1000Nm, then we take the impact gun and see if we can undo it. If so, you can indeed say the tool has a Bolt Busting torque of 1000Nm. Could the impact gun do a fastener up to this torque? Certainly Not – but given the right conditions, it is possible to rattle the nut loose. Would this so-called Bolt Busting / Nut Busting / Ultimate or Breakaway Torque, ever be of use in the real world – No because the test has been designed in such a way that it predisposes the fastener to come loose. In real life fasteners are designed not to come loose, they employ bolt stretch and friction to hold the fasteners tight. So aside from providing a high figure to use on your advertising it is a relatively meaningless figure in regard to real life applications.
Whether it is correct to advertise in this way or not, may be a debatable point, but the world being what it is, once some manufacturers started, all other had to follow suit or suffer a decline in their sales.
As such we have a situation where companies such as SP Tools who choose to remain open with their customers publish both the “Working torque” and the “Bolt Busting torque” in their specifications so as to compete with the competition on a level playing field while at the same time keeping the customer informed of the real-life capability of their tools.
