Who wants to find out that they had a stripped head bolt first thing in their rebuild? More often than not you did too much torque with that wrench. Twenty foot pounds turned into thirty turns, and now there’s some patience lost, money spent and time wasted.
The industry standard Snap-on torque wrenches is what they are because of how well they work, but the best ones will still drift. Calibrating one yourself not only saves you service charges but also allows you to trust those hands when it realy counts. In my experience, most mechanics believes calibration is an annual calendar event.
Nope. Calibration is a condition based process. Let’s say you dropped the tool, used it past its upper range, let it sit unused for years and the internal mechanism shift.
Continuing without verifying accuracy is gambling with every fastener you tighten. Verify accuracy before trusting this tool for critical work. You are gathering tools for the job.
Steps To Calibrate Your Snap-on Torque Wrench
Why Calibration Matters
First you’re going to want a known good reference wrench or a test stand. A lot of shops makes their own with a lever arm and a digital force gauge. Snap-on sells these special testers too.
Gathering Calibration Tools
The math here isn’t hard but it doesn’t forgive much either. Force times distance equals torque. And if your arm length is off by a fraction of an inch, you’re screwed.
Calculating Torque Accurately
So measure the distance from the center of the square drive to the pivot point. Write that number down. That’s what everything else is built on.
Next, set your wrench to about halfway through its operating range. For most Snap-on wrenches this will be from twenty to eighty percent. If you have a wrench with an upper end of one-hundred-fifty foot pounds then select a number such as one-hundred.
Adjust your wrench up until it reaches that point. Now use your force gauge to see what amount of force was needed. Write that down.
Adjusting the Calibration Nut
That is your starting point. Now we need to know how far out of whack the wrench are in its sweet spot. Tweak the calibration nut on the handle The mechanical heart of adjustment is the calibration nut in the handle of your click type wrench.
Inside the handle there should be a threaded nut that adjusts the spring tension. The tighter the nut is turned the more force it takes to break the ratchet. The looser it is turned the less force it takes.
Go slow and make small turns. You can increase or decrease several foot pounds with a quarter turn. If you’re impatient, it’s easy to overshoots.
Verifying Accuracy Across Range
Here, patience trumps strength. Recheck the setting at two other points. Just because you are accurate on a single number doesn’t mean you’re accurate throughout your range.
Check near twenty percent (low). Now check near eighty percent (high). The tool should read linear.
It will say something like fifty pounds and show it’s low, it shows a hundred pounds and then says it’s high. That means maybe the mechanism is binding. Calibrating a broken spring won’t help.
Send that wrench back to Snap on for proper repair. Lock it down After you get to your desired reading with some wiggle room, you’ll want to go ahead and tighten the lock nut into place. Snap-on wrenches even feature an extra lock so they don’t move around and throw off your calibration while you use them.
Locking and Storing Your Wrench
Make sure this lock has good tension too. You don’t want a loose lock in your toolbox. That’s a ticking time bomb.
Leave that wrench at the lowest setting. Doing so takes the pressure off the internal spring and keeps it calibrated for a long time. I know it seems like you should of have it loose, but the physics are clear: A relaxed spring is a true spring.
A compressed spring fatigue. Take care of your tools; they’ll take care of you. Keep your bolts in place to keep your peace of mind.