There's such tool called impact driver (like this one for example). The manual says it uses a special mechanism to produce a series of torque impulses to fasten/loosen nuts and screws.
The tool has only two adjustments - the forward/reverse switch and the On/Off switch. The deeper the On/Off switch is pressed the faster the tool motor rotates.
There's no clutch to adjust the torque value after which the clutch would disconnect the motor. How do I control the torque without a clutch?
Suppose I need to assemble a section of fence that will require say one thousand screw/nut connections with nuts of the same size (that's not an imaginary task - I did such job without an impact driver). Obviosly I need to tighten all nuts to more or less the same torque. If I overtighten a nut it can just break or cut the screw or bend the parts it connects - that's bad. If I undertighten a nut it will soon loosen and fall out - that;s bad as well.
So let's pretend I use nuts that need to be tightened to approximately 70 Newton-meters and the driver I use is said to produce torque up to 100 Newton-meters.
And of course I need to drive those nuts fast - otherwise why would I use a power tool instead of a screwdriver and a usual wrench? So obviously I can't time the periods of applying torque or count impacts or whatever else - I need some reliable way to achieve more or less the same right torque for all nuts.
Please note: I don't care of achieving exactly the right torque. I only care of achieving more or less the required torque - so that the nuts don't loosen on themselves and parts are not damaged while the nuts are being tightened. The primary concern is that the driver works very fast, so if I hold the switch pressed for just too long I can easily overtighten the nut and cause unintended damage.
How do I achieve roughly the same torque repeatedly for multiple nuts when using an impact driver?