A torque wrench is an essential tool for anyone working on machinery, vehicles, or other mechanical equipment. It allows you to tighten bolts and fasteners to a specific tightness (torque) to ensure proper function and prevent over or under tightening. Learning how to use a torque wrench correctly is important for safety, proper assembly, and preventing damage. This comprehensive guide will teach you everything you need to know about how to properly use a torque wrench.
Selecting the Right Torque Wrench
There are a few key factors to consider when selecting the right torque wrench for your needs:
Type of Torque Wrench
The two main types are:
- Beam – Has a pointer that indicates the torque setting on a scale. More accurate but requires more care in storage and handling. Best for very precise applications.
- Click – Emits an audible “click” or “beep” when the preset torque is reached. Easier to use but less precise. Good for general automotive/machinery uses.
Drive Size
Make sure the drive size (1/4″, 3/8″, 1/2″, etc) matches the bolts/fasteners you’ll be working with.
Torque Range
Select a wrench with a torque range appropriate for your application. For smaller fasteners and precision equipment, you’ll need lower torque ranges (25-100 ft-lbs). For automotive or machinery, higher ranges like 30-250 ft-lbs are common.
Accuracy
Beam style torque wrenches often have finer gradations on their scale for greater precision (+/- 3% accuracy is common). Click wrenches may have +/- 4% accuracy.
Ratcheting vs Non-Ratcheting
Ratcheting torque wrenches allow you to tighten down to the preset spec in smaller increments. Non-ratcheting require tightening in one motion.
Features
Higher end torque wrenches may have other features like digital displays, interchangeable heads, memory settings and more. Consider options you may find beneficial for your work.
Setting the Torque
One of the most important steps in using a torque wrench properly is setting it to the required torque spec for the application:
- Beam Style – These have a scale along the handle. Locate the desired torque setting and line up the indicator to match.
- Click Style – There will be a way to adjust/set the pre-load such as a dial, knob or screwdriver-adjusted collar. Consult the manual.
- Digital – Allow you to set a precise torque spec digitally. There are buttons to increase/decrease the setting.
- Convert Units – Torque specs may be in Nm, ft-lb, in-lb. Make necessary conversions to match wrench units.
- Always double check the torque setting before use to avoid mistakes.
Torque Sequence
The order you tighten bolts can be important to avoid warping or distorting parts. Follow any sequence recommended by the equipment manufacturer. General tips:
- Start fasteners by hand before final torque.
- Tighten opposing bolts in sequence to equalize force.
- Tighten from center outward in a crisscross pattern.
- For wheels, use a star pattern sequence.
Tightening Technique
Proper technique when tightening with a torque wrench is vital for an accurate torque reading:
- Hold steadily in-line with the axis of the fastener. Avoid bending.
- Pull smoothly in a steady motion. No jerky movements.
- Do not use extensions unless approved by the manufacturer.
- Use on nuts only, not bolts or sockets in a drill.
- Ratcheting types: Use smooth strokes back and forth until the preset torque is reached.
- For click wrenches, note when the click occurs so you stop immediately.
- Do not over-tighten once the preset torque is achieved.
Reading the Torque
When using a non-clicking beam style torque wrench, you’ll need to monitor the torque as you tighten:
- Beam Deflection – Note the difference between no load position and position when tightening. This deflection indicates the torque applied.
- Go slowly to allow the beam to track along the scale.
- Stop tightening when beam position matches preset torque. No deflection = no torque.
- Allow beam to return to rest position after each use.
Torque Wrench Maintenance
Proper handling and care will maintain the accuracy and condition of your torque wrench:
- Never exceed the wrench’s maximum capacity. Can cause internal damage.
- Return the setting to lowest reading when not in use to release internal spring tension.
- Beam types must be set to 0 when not in use to prevent inaccuracies.
- Store carefully in protective case to prevent shocks or drops.
- Keep free of dirt, grease and moisture. Wipe clean after each use.
- Only use accessories and adapters designed for that specific torque wrench.
- Lubricate hinge points occasionally with light oil.
- Follow all guidelines for maintenance from manufacturer.
- Calibrate annually to maintain proper accuracy.
Safety Tips
- Inspect torque wrench before each use for any damage or issues. Do not use if malfunctioning.
- Ensure you are using the correct size and type of wrench for the application.
- Double check the torque setting before tightening.
- Make sure you grip the wrench properly and pull in a straight line with the fastener’s axis.
- Beware of pinch points and do not hold sockets or accessories by hand. Use a wrench or extension.
- Take caution if switching between standard and reverse directions.
- Wear proper PPE such as gloves, eye protection.
- Do not use makeshift extensions or cheater bars for added leverage.
- Do not use to “break” fasteners loose initially.
Common Torque Wrench Mistakes
It’s easy for improper use of a torque wrench to cause inaccuracies or tool damage. Be aware of these mistakes:
- Not returning to 0 between uses for beam style.
- Jerking or yanking during tightening motion.
- Continuing to pull after clicking or reaching preset torque.
- Forgetting to re-check torque setting.
- Not holding directly in line with axis of fastener.
- Using wrong drive size or extensions.
- Exceeding maximum rated torque.
- Not regularly maintaining and calibrating.
Choosing Alternatives
In some cases, there may be alternatives that can provide adequate tightening without requiring a torque wrench:
- Torque Sticks – Provide preset amounts of torque for impact drivers. Easier but not extremely precise.
- Torque Angle Meters – Measure the angular rotation during tightening. Requires some calculation.
- Bolt Stretch Method – Measure the minute lengthening of the bolt as it stretches under tension. More involved.
- Torque-to-Yield Fasteners – Designed to release at a pre-set load. Used in aerospace/critical applications.
However, for precision, consistency and control, a true torque wrench is hard to beat.
FAQs
What should I do if my torque wrench isn’t giving an accurate reading?
- First, check that you have correctly set the wrench to the right torque for the job. Double check the wrench’s settings before use.
- The torque wrench may need maintenance or calibration if it is consistently off. Follow the manufacturer’s instructions.
- A damaged or worn torque wrench that is beyond repair will need to be replaced.
Why do I need to keep returning a beam wrench back to 0?
Continually leaving a beam style wrench set to a torque reading will cause the internal spring to take a “set”. This leads to inaccurate readings over time. Always reset to 0 to maintain accuracy.
Should I oil or grease my click-style torque wrench?
No, click-style torque wrenches are not usually lubed and introducing oil or grease can damage the precision internal mechanisms. Only use oiling or greasing if specifically instructed by the manufacturer.
What are some examples of things that would require a torque wrench for assembly?
- Automotive – Lug nuts, cylinder heads, wheel bearings
- Machinery – Gears, pumps, compressors, presses
- Aerospace – Control surfaces, engines, airframes
- Bicycles – Stems, bottom brackets, cassettes
- Firearms – Receivers, barrels, scopes
How can I determine the proper torque range and drive size I need?
Check the equipment manuals for recommended specs. If unavailable, identify the thread size and typical grade of fasteners used. Cross-reference a torque chart or consult with experts to determine proper torque range and matching tool drive size.
Why do I need a calibrated torque wrench instead of just tightening until it “feels right”?
Relying on just a subjective “feel” often leads to inconsistent tightness on fasteners. A calibrated wrench ensures you tighten to the exact spec needed for proper function, safety and life of the equipment. The precision helps prevent over or under tightening.
Conclusion
Learning to use a torque wrench properly is an essential skill for anyone working on mechanical equipment. Follow the guidance in this article to select the proper wrench, set it correctly, use proper technique, and maintain the wrench in good working order. With practice and care, a quality torque wrench will provide consistent, accurate tightening for the life of the tool. Always keep safety in mind, double check your work, and take steps to prevent common mistakes. A properly used torque wrench is one of the most vital tools for any toolkit.