Torque Screwdrivers - What do you use?

Question

Hi

I work at Newark and I'm reviewing Torque Screwdrivers. Do you use them? If so what increment range is common and are you using metric or imperial.

My background is in rough electrical work, but I'm interested in how the torque screwdrivers are used by engineers or if they are used in PCB assembly.

Thanks

TB

rsc · Answer

Hi Tom, When I worked for Bosch we used many types of torque drivers from a few g-mm to several hundred Nm. To get the best control of clamping force, you need a device that also measures rotation angle. We used CDI Computorq wrenches in the labs for manual work, not sure about the automated ones in the factory, they seemed to keep their calibration better than other brands we tried. A fastener will be most effective in the 60-80 percent range of its elastic region. Torque alone cannot guarantee clamp force. Many things can affect whether or not vibration will loosen a screw, including surface finish, oils and lubrication, dirt in the threads, use of Loctite or other thread adhesive. Here's a diagram of a typical fastener torque curve: http://www.extreme-bolt.com/images/Applications/Torque/Torque_Curve.jpg Scott

abrain · Answer

Hi Tom, I’ve recently been using one of these Wera Wera torque screwdrivers, which goes up to 3Nm and was ideal for the M3 screws used to hold some enclosures together. Personally it’s rare I use them, as usually I subcontract final assembly, this was a case of needing to do some field upgrades and ensure the units weren’t going to shake apart afterwards! This 3Nm range seemed ideal for screws up to M3, for fitting these enclosure onto other equipment or mountings I’d probably look to a torque wrench instead for the M4 or M5 fasteners that usually get used in the industries I deal with. You can see I’m pretty much metric, for the fasteners, but appreciate the options a 1/4” drive brings! Hope that helps! A

tbartonnewark · Answer

I meant "torque". What weight / increment range? Metric or imperial "inches"

three-phase · Answer

Personally I have only really used torque settings on high current electrical apparatus and batteries which is well out of the range offered by torque screwdrivers.

The use of torque screwdrivers in the UK within the electrical industry is becoming more wide spread mostly because of the interpretation of a regulation in BS7671 and the drive by the assessment body inspectors who have started to push for their use when the carry out assessments on electricians.

The regulation requires electrical accessories to be installed in accordance with the manufacturer's instructions and a number of manufacturers now are starting to add torques settings for consumer units and MCBs into their literature.

Popular units in the UK are from Wera and Whia, both are VDE approved and go up to 3Nm. Screwdrivers generally need a yearly calibration to be compliant. As I am UK its metric I am afraid.

They are not a popular choice with old school electricians, but interestingly they can be effective for preventing over-tightening, that can damage the apparatus, just as much as not getting the terminals tight enough.

Kind regards

doug65 · Answer

Where I work we do a variety of torque control applications: My preference is to use an electronically controlled tool. (Atlas Copco / Weber) These give an advantage of being able to control the speed in which the screw goes in. You can also report torque angle which helps in finding a stripped or cross threaded screw. A toll set-up would cost several thousand dollars, so not economical for a few screws. When just needing a few screws I would suggest using a calibrated gage quality tool. I do calibrations for the company I work and have calibrated many store brand torque tools for employee home use and see them be off by 30% right out of the package. If it is important enough to check it might as well be right. As far as metric or imperial, most specifications are metric for our use.

Torque Screwdrivers - What do you use?

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