The Economics of Torque Tool Calibration

May 16, 2003
/ Print / Reprints /
ShareMore
/ Text Size+
The cost to calibrate torque tools can add up quickly. Learn how to choose the most cost-efficient calibration program for your company.

Torque tool calibration cost control does not normally appear to be a large ticket item--a few dollars here, a few dollars there. That is, until the true costs are analyzed. Many companies do not realize that their annual torque tool calibration costs may significantly exceed the torque tool purchase costs associated with acquiring new torque tools.

In the past few years, torque tool calibration technology has rapidly changed, and this has opened new calibration options for manufacturers. Knowledge of these options permits a more informed and objective decision on what is the best course for each company. But knowledge of options is not enough. A means of analyzing the costs and benefits, as fits each firm and operation, is essential to making the best business decision. A basic spreadsheet that can be used by any company to analyze costs can determine the best course for a firm to take.

No more guesswork
Early mechanical torque analyzers used springs and other mechanical means that were subject to high variation. Compounding the problems this created, the results were usually displayed by a pointer moving over a dial or a light beam across an etched glass face. These methodologies required the operator to interpolate the torque. Interpolate is a fancy word for guess.

The early electronic systems eliminated the bulk of the interpolation and markedly improved accuracy. Yet, they still fell short of fulfilling end-user needs. Current digital systems offer significant advantages, and open new options for the torque tool user.

Because of the improvement in technology, almost any power tool can be tested. There are still barriers in the area of impact wrenches, but torque wrenches of all types, and all non-impacting power tools can be tested.

Today's digital testers permit the average technician to quickly learn how to use them to calibrate torque wrenches and power tools. The reliability of digital circuitry has made the torque testers as reliable as any other piece of digital equipment. This is a large change from prior generations of testers.

These technological changes mean that the users of torque tools can in many cases calibrate the tools themselves, and need only rely on torque tool OEMs for calibration if this strategy is the most cost-effective means for their particular operation.

The testers have followed the pattern seen in so many digital devices--cost remains stable or reduces while quality and features increase. Digital testers are available with accuracies that range from as wide as + or - 1% to as tight as + or - 0.25%, and are capable of electronic integration into existing gage control and QA systems.

Some torque tester designs are so simple and inexpensive that they can be deployed as "line checkers"--used by assembly personnel to test their tools at the start of each shift or immediately when any question arises. Lineside verification permits use of extended calibration intervals, thus controlling costs while enhancing process reliability.

The required accuracy of the tester is easy to determine. A critical 4:1 tester-to-tool ratio must be maintained or exceeded. This means that the tester must be at least four times as accurate as the torque tools it will be used to test.

To provide high quality and efficiency to the user, tester manufacturers realize that stand-alone equipment is no longer sufficient. Most of the calibration equipment offered today can be integrated into the existing gage control systems used by the purchaser. Digital testers are commonly equipped with serial ports to permit export of calibration data directly into a PC, for use with gage tracking or calibration software.

The 4:1 accuracy ratio between the tester and the torque tools to be tested is essential. Just as calipers are not calibrated with a yardstick, torque tools shouldn't be calibrated with a device of insufficient accuracy. This ratio is a key consideration.

The second factor is the mode of operation, which refers to the way the tester handles the raw signal output from the sensor and determines the actual torque to display. Different types of torque tools require different modes of tester operation. The mode of operation that determines the peak output of a power tool is different from that used to check an indicating torque wrench such as a beam or dial type.

The third criterion is cost. The cost can only be determined after the first two criteria are addressed. Determine what is needed from a piece of equipment before looking at the equipment itself and the costs associated with it.

Calibration Strategies
Manufacturers have four calibration strategies from which to choose: factory calibration by the tool manufacturer; external calibration services; an internal torque tool calibration program; or a blend of these three strategies.

In spite of appearances, each of the first three strategies is more complex than it appears. The cost and operational ramifications for each strategy differ not only by method, but also by manufacturer and location. But what are the advantages and disadvantages of each?

The simplicity of the factory calibration is its greatest appeal. The tool user sends the tool out, gets it back later, files the certification and pays the bills. It is easy to do. Torque tool manufacturers love this method because it provides them with a nice revenue stream.

Factory calibration has its disadvantages. It has the longest out-of-service time required of any of the three basic strategies, and it typically has the highest ongoing expense level.

The time the tool is out of service when the factory calibration strategy is used is measured in weeks. Even if the factory were to turn the tool around the same day it arrived, barring overnight delivery, shipping time would assure extended downtime for the tool.

This method is usually the single most expensive means of maintaining torque tool calibration. The ownership cost of the tool is quite high in this strategy.

Calibration Services
Calibration services are the most difficult strategy to analyze on an industry level. Because calibration labs are not all the same, any given lab may or may not offer the combination of technical expertise, versatility, price and services to make it the most cost-effective calibration strategy for the torque tools in any given operation. The service may be local and offer pickup and delivery. It may perform calibration on-site. The price may be the same as or less than factory calibration and it may have few hidden costs. Services may offer ISO- or QS-acceptable calibration certificates. Because of the variety of services that calibration labs offer, the torque tool user has at least a modest menu of services from which to choose.

Unfortunately, some calibration service firms are not qualified to perform torque tool calibration. They also may not be repair-capable on any given company's particular brand of torque tools. And finally, not all calibration service firms are ISO- or QS-registered--a significant consideration.

Calibration services also face the difficulty of dealing with many tool brands and designs. It is extremely difficult to be expert in all brands and designs of torque tools, and stocking parts to repair even the top brands in any tool category can be fiscally difficult at best. Thus in any given area, torque tool users may or may not be able to find the repair expertise for the brands of torque tools they own.

Further, many calibration labs do not address torque calibration. Torque is a force, not a dimension. Many labs with a high degree of expertise in dimensional measurement and calibration have little or no expertise in force measurement and calibration.

Another potential disadvantage of outsourcing to a calibration service is turnaround time. The actual business of calibration laboratory services is subject to many of the same vagaries that are faced by manufacturing firms. Business does not flow in the door in a nice orderly manner--it has surges and slack periods that can affect the time required to perform the calibration. Vehicles and equipment sometimes go out of service, even when well maintained. This can affect the ability to deliver on-site service on a timely basis.

In-house calibration
The third option is to establish an internal torque tool calibration program. This method offers the least out-of-service time of the three strategies.

Internal calibration is fast. The downtime associated with shipping to, and receiving from, an external facility is eliminated. Internal calibration even eliminates the time that would be spent waiting for the calibration service to show up in the event a question arises.

Because external overhead and profit markups associated with external service suppliers--whether OEM or calibration lab--are eliminated, and shipping and handling costs are eliminated, this strategy starts with a significantly lower cost.

The ability to dovetail torque tool calibration into an existing dimensional tool calibration system provides consistency and ease of execution.

Deciding to establish an in-house torque tool calibration program shouldn't be a snap judgement, however. Doing it in-house requires ongoing conformance to calibration specifications. It requires investment in torque tool calibration equipment as well as employee training.

As with manufacturing and dimensional calibration, torque tool calibration requires those performing it to adhere to the procedures and specifications set up to properly execute it. Those firms accustomed to following procedures and adhering to specifications will find internal torque tool calibration easy. Those that have difficulty in those areas as applied to manufacturing and dimensional calibration will find that internalizing torque tool calibration merely extends the reach of their problems.

An investment in the equipment and training to effectively calibrate the tools in the facility is required. Digital torque testers are available in price ranges varying from as low as about $1,500 to $65,000 and up. The training required can usually be accomplished in a few days. This can be somewhat extended if there are numerous brands and designs of torque tools in the facility.

Despite the investment, it is important to remember that there can be no return on investment, or ROI, if there is no "I" to get the "R" on.

Blended Strategies
Blended strategies come in many varieties. The greatest limitation in combining OEM/calibration lab/internal torque calibration strategies is lack of imagination by the user. Treating each of the three traditional approaches as simply a menu from which your firm can choose "a la carte," and deploying each only as it provides demonstrable operational and economic advantage over the others, can provide superior cost control and operations enhancement.

All of the possible combinations of blended strategies cannot be covered here, but there are a couple of general rules to consider. Torque tool calibration can be divided by precision, using external sources for more precise tools and internal sources for less precise ones. It can instead be divided by tool type, using internal sources for some and external sources for others. Alternatively, calibration can be divided by function, using internal resources for calibration and external sources for repair only.

As a rule of thumb, the more complex or precise a torque tool is, the more it will cost both to purchase and operate the appropriate torque tool tester that is required to calibrate the tool.

At what cost?
Frequently, the hardest part of selecting the best strategy, or blend of strategies, for any given calibration operation is the economic analysis. A spreadsheet can assist in that endeavor and can indicate the level of cost associated with each.

The starting point for the economic analysis is to determine how many and what type of torque tools there are in the shop and how often they should be calibrated. This is seen in the spreadsheet chart, "Torque Tool Calibration Cost Analyses."

The torque tools are differentiated by the accuracy specifications applicable to each. In the example shown, each of the two tool types being analyzed--power tools and clicker torque wrenches--require the same accuracy specification of + or - 4%. Keeping the tools separate from the beginning provides a clear picture, eases tester type selection when considering internal calibration, and provides easier exploration of blended strategies.

In the first line item, enter the number of tools that should be calibrated. The second line is for the number of times per year that a tool is to be calibrated. For quarterly calibration, enter the number 4. For monthly calibration, enter the number 12. In the example, there are 12 power tools and 12 clicker torque wrenches in the factory. Each of these tools must be calibrated 4 times a year, which means that there are 48 total calibrations for each tool type required over the course of a year.

Factory calibration costs
The next section of the spreadsheet, "Factory Calibration Strategy Cost Com-ponents," looks at the direct costs, and most of the more obvious indirect costs, of each individual calibration. At this stage, do not attempt to quantify any of the other indirect costs associated with external services, such as purchase-order generation and processing, or payment processing.

The first line item is packaging costs. Enter the cost of packaging materials needed to send out one torque tool. That number, by type, goes in the appropriate column on this line.

The next line addresses the labor required to send the tool out. It most commonly takes about 10 minutes to perform the clerical tasks necessary to prepare and generate the documents required to get the tool into the hands of either the post office or overnight carrier. Allocate 1/6 of an hour at the average hourly rate as the cost of performing this task. If the average hourly rate is $12, the amount for this line would be $2.

The third item is actual shipping cost, regardless of shipper. Use actual costs previously experienced and paid so you have the most accurate rates. The next item is the actual calibration charge the factory bills for calibrating that type of torque tool. Again, use the quoted numbers or prior history.

Next, determine the cost of backup tools, if they are needed when the primary tool is being calibrated. In the spreadsheet, under other hidden costs, enter 1% of the purchase cost of a second tool. Use 1% of the purchase cost because most torque tools will last at least 100 calibration cycles under such circumstances.

At the bottom of the form is the estimated annual cost line. The spreadsheet here multiplies the number of annual calibration cycles by the sub-total of direct and indirect costs plus the backup tool costs, and presents the dollars spent. Note, the estimated annual costs are based on the company's experience; its quantity of tools, shipping costs, billed calibration charges and labor rates. All that has been done is quantification of the costs experienced.

Calibration service costs
To analyze the true cost of a calibration service, start with the number of tools and frequency of calibration by tool type. While cost categories remain the same, they are divided into those which will definitely be experienced, such as fees charged by the calibration service, and those which may or may not be experienced such as shipping.

As an example, a local calibration service does the calibration on-site for $25 per tool and $2 per certification. Because all tools are to be certified, the actual total charge is $27 per tool. When the cost per calibration is multiplied by the number of calibrations, the annual cost is obtained.

Internal calibration costs
The starting point for analyzing the cost of internal calibration is the same as in the previous examples. In this case, the cost to calibrate 12 clicker torque wrenches and 12 power tools, each calibrated quarterly, is analyzed.

With internal calibration, the cost categories pertinent to shipping and receiving are eliminated. There is effectively only the cost of the calibration time and the internal paperwork time.

Assume both that the tester is calibrated annually and that the cost of the tester calibration is more than twice the projected annual expenses for internal torque tool calibration, at $600. This still yields a savings of greater than 50% over either prior scenario.

The advent of new-generation digital torque testers has created the opportunity for torque tool users to develop reduced-cost calibration strategies specifically for their operation. Economic analysis of the various options available permits the torque tool user to customize their strategy to obtain the most cost-effective calibration possible.

Did you enjoy this article? Click here to subscribe to Quality Magazine. 

You must login or register in order to post a comment.

Multimedia

Videos

Podcasts

Charles J. Hellier has been active in the technology of nondestructive testing and related quality and inspection fields since 1957. Here he talks with Quality's managing editor, Michelle Bangert, about the importance of training.
More Podcasts

Quality Magazine

CoverImage

2014 December

Check out the December 2014 edition of Quality Magazine for features!

Table Of Contents Subscribe

The Skills Gap

What is the key to solving the so-called skills gap in the quality industry?
View Results Poll Archive

Clear Seas Research

qcast_ClearSeas_logo.gifWith access to over one million professionals and more than 60 industry-specific publications,Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

STAY CONNECTED

facebook_40.png twitter_40px.png  youtube_40px.pnglinkedin_40px.png  

eNewsletters