Torque Wrench Calibration

Mechanics rely on torque wrenches to provide accurate and reliable torque readings so they can apply the right amount of force on the nuts and bolts in a vehicle. However, torque wrenches need to be calibrated regularly to make sure they're giving accurate readings. While it may be best to take your torque wrench to a professional for calibrations, you can do a pretty good job of keeping your torque wrench accurate by calibrating it at home.

It should come as no surprise to anyone reading this that torque wrenches are calibrated and that calibration should be checked, at least occasionally. According to some experts, torque wrench readings have a tendency to change following 2,500 to 2,800 repetitions. This can also be accelerated by improper storage (for example, not keeping the torque wrench in the case when storing it, allowing it to drop to the ground when using it, not taking the tension off the wrench when in storage and so on). The main reason for this is because most clickers are constructed with internal springs and those springs can lose tension (and lose length) over time.

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For something like an 18 inch wrench such as the older torque wrench shown in the accompanying photos, measure back from the square drive to the center of the handle (15 inches from the square drive in our example) and mark the handle. This is a reference number. Write it down.

Next tie a known amount of weight to the torque wrench at the marker on the handle (15 inches in our case). The idea here is to set the clicker to a specific number, hang weight off the end of the wrench, and see where it clicks. For this setup, we used common exercise dumbbell weights to come up with the 20 pounds we needed. This includes three five pound weights plus a five pound handle assembly. The math works out like this:

To make the adjustment, take the weight off, and then repeat the process by adding the known weight to see if the wrench clicks. Keep repeating the process (adjusting the tension on the spring) by lifting the weight off the torque wrench handle and lowering the weight again. Turn the set screw and check to see if it clicks.

Move the weight in one inch increments up the handle (closer to handle end). The idea is to determine where the wrench clicks using the same, known weight. If, for example, the wrench clicks at 16 inches (and it is set for 25 foot-pounds), the math for correction works out like this:

When you use the wrench, multiply the wrench torque reading by the calibration figure. For example, with the above correction factor, the wrench will click at 25 foot-pounds, but the true reading is 25 X 0.937 = 23.425 foot-pounds.

All your test proves is that the wrench clicks at torque values up to and including 25 when tested with 25 pound weights. How did you determine that the same setup would not have clicked at 26, 27, 30 and up? You never established the value the torque wrench clicks at with your weight

CDI Torque Calibration Systems, Transducers & Accessories are the most sophisticated systems available in the industry. These torque wrench calibration systems will test and calibrate most types of torque wrenches, torque screwdrivers, torque multipliers, cable tensiometers, tension and compression gauges and non impact power tools such as nut runners and electric screwdrivers between the ranges of 4 In oz to 2,000 Ft Lbs. Use this CDI torque wrench calibration equipment to increase productivity today.

The double beam ones hold their calibration quite a bit better than the click ones, and are calibrated to a tighter tolerance. Buying an inexpensive beam one to keep in a drawer and check your clickers against gets you most of the way.

The digital will be very precise, but precision =/= accuracy. A beam wrench will always be fairly accurate(as accurate as the scale painted on it), as there is so much less to go wrong and its all visible(i.e. bent pointer). Good enough to keep a clicker calibrated close enough for hobby work.

Where my old man works everytime they send out a torque wrench for calibration it comes back non-calibratable and therefore junk. To test a torque wrench my father just gets one in calibration and torques the non-calibrated on against the calibrated one to see how far off they are. Good luck and let us know what you find out.

Bravenrace, I understand your question. I use to work in a chemical plant, and calibrating scales was always an issue. You can't package things accurately if you are not accurately calibrated, and they could loose calibration virtually anytime being bumped, etc.

Apparently Bravenrace is the only guy here who read his user manual that came with his torque wrench which recommends recalibration every 2500 repetitions, or approximately once per year for most users.

I picked up a nice old Proto 1/2" torque wrench and asked the tool repair shop to calibrate it. He said "sure thing, runs $80" I said "On second thought...." and picked up a $35 digital torque adapter he had on a rack. He just winked at me.

This seems reasonable if you have a "calibrated" weight and understand the error in your distance measurement. You would want to at least test the high end of the wrench and the low end. Some points inbetween wouldn't hurt either.

As testing has shown in plenty of magazines, all new torque wrenches are calibrated decently from the factory. Getting yours recalibrated will cost more than it does to just buy a new one (probably), especially if you have to ship it anywhere.

Me, I bought a beam wrench for $20 and check my SK Tools clicker against it every once in a while. According to that, the SK hasn't needed recalibration in the 15 years I've owned it. But I'm just a hobbyist user. I also always relieve the spring pressure when putting it away.

Just went out and tried the weights hanging on it a foot out. Clicker style craftsman. The torque wrench was about 4% off at 58 lb*ft setting. It would just barely click with 56 pounds gently hung from it. Wouldn't click at 59 lb setting. Easy peasy lemon squeezy.

I'm the quality manager at an ISO-17025 accredited lab, but we don't do torque, only plating and coating thickness. If you want to get technical, check out A2LA.org for accredited labs that do torque. (Probably $$ but guaranteed to be what you are looking for.)

To determine whether it makes economic sense to establish your own service center, consider the unit cost of each calibration. The unit cost of in-house calibration equals the initial and ongoing costs of your in-house service facility, divided by the number of tools you expect to calibrate within a given period. If your in-house unit cost is sufficiently lower than the service center cost, so as to generate a return on your investment within a reasonable time frame, then it makes sense to invest in your own service center.

I proceeded to open up the wrench and figure out the contact cleaning, described in detail above. Hopeful, upon completion of the cleaning, i again tested the wrench: same brief all-zero display, same quick auto shutoff. Torquing the wrench produced no reading on the digital display and no LED indications. I soon realized that the factory calibration had been erased!

Received the torque adapter and ran it through its paces. Once stupid user error was overcome, it proved itself to be fully functional. I attached it to the Craftsman torque wrench, with it being sandwiched between the head of the Craftsman and its included aluminum block, clamped tightly in the bench vise.

With the Craftsman wrench in place but off and the Powerbuilt on, i arranged three different paint bucket-based loads, one for each weight calibration point needed by the 47711 wrench. I simply adjusted the load until the torque measured spot-on on the Powerbuilt. At that point, i was able to power up the Craftsman and go through the calibration procedure listed above.

Our team of calibration technicians are able to assess an array of torque instruments and make adjustments as necessary to ensure that tools remain compliant with their defined standards, ranges and accuracies.

These two calibration standards have been devised by the International Organisation for Standardisation (ISO) specifically for Type I (indicating) and Type II (setting) torque tools. Each standard details the requirements and procedures necessary to maintaining conformance with various Type I and Type II torque tool specifications. Please see below for an overview of each standard.

The ISO 6789-1:2017 standard can be used to determine a declaration of conformance. It details the conformance tests, marking requirements and minimum requirements needed for a Type I (indicating) or Type II (setting) hand torque tool to achieve a declaration of conformance.

This standard pertains specifically to hand torque tools classified as indicating (Type I) and setting (Type II) torque instruments such as those used for the controlled tightening of screws and nuts.

This standard can be used during static (step-by-step) and quasi-static (continuous) calibrations. In these instances, the torque of the instrument-under-calibration is defined by measuring the elastic form change of a deformable body, or is determined using a measured variable which is in proportion to the torque.

As a national company, PASS Ltd is able to calibrate torque equipment in our lab or at your premises. Please contact our calibration team to discuss which of the three options listed below would best suit your requirements:

On-site calibrations are recommended for those with large amounts of equipment that would be impractical to send via courier; instead a PASS Ltd calibration technician will come to your site to perform the necessary calibrations.

To check tool calibration, inspect the pointer when the tool is at rest. If it is pointing at 0, the tool is calibrated. If it is off zero, bend the pointer shaft unit it points at 0. Place a screwdriver or similar lever between the two beams closer to the head than the scale. Bend the small shaft until the point is at zero when the tool is at rest.