Electric Screwdriver Torque Tester

A clutch that is set by feel drifts as the tool warms up and as the bit wears. The measurement that stops the drift is the reaction torque at the moment the clutch slips, taken on the same fixture every time.

Product overview

The tester is a bench instrument: a rigid reaction head, an adaptor on its shaft, and a display unit that holds the peak. The tool is held on the adaptor with its body restrained, so that when the clutch releases, the torque goes into the sensor rather than into the operator.

This generation of the range puts the controls a production bench actually uses on the front panel: unit selection, mode, peak reset, a store and recall pair, an average key and a print key. The stores hold the settings for a set of products, so a changeover is a number rather than a fresh setup.

How the electric screwdriver torque tester works

The sensor is a strain-gauge bridge in the reaction head. Torque applied to the shaft strains the bridge, the bridge produces a small voltage, and the instrument converts it to a torque reading in the selected unit.

A clutch does not deliver a steady torque. It rises until the clutch slips, drops away, and the motor recovers; the useful figure is the top of that first rise. PEAK holds it. TRACK shows the signal as it happens, which is what is needed to zero the instrument before a run and to see whether a tool is slipping early or late.

Averaging exists because a single slip is noisy. Several readings are taken and the mean is used, which is the number a clutch adjustment should be made against. The upper limit is set from the same figure: a reading above it lights the lamp and sounds a long alarm, so a bench can sort without reading the display.

How to select the right electric screwdriver torque tester

Begin with the setting the clutch has to hold, not with the tool’s maximum. A tester is at its least accurate near the bottom of its range, so the working torque wants to sit in the upper half of the scale while the tool’s highest clutch setting stays inside the full scale.

Then look at the screw. A machine screw driven into metal needs a different size from a self-tapping screw in plastic, and a precision driver on a small electronic assembly needs a smaller size again. Choosing one size for both ends of a plant usually means the small work is measured on a scale that is too coarse for it.

Then check what the bench does with the result. Where the reading has to be recorded, the interface and the store matter more than the display; where the operator reads and adjusts on the spot, the alarm and the peak hold matter more.

Finally, confirm the adaptor. The tester measures at the tool’s output, so the adaptor has to match the bit holder or drive in use, and a tool with an unusual nose needs that settled before the order rather than after.

Measurement limitations and selection considerations

The reading is only as good as the fixture. If the tool body is allowed to move, part of the reaction is absorbed by the movement and the peak reads low; if the adaptor is loose on the shaft, the peak reads high and erratic. Both faults look like a drifting clutch.

Torque is measured at the tool output, which is not the torque at the screw thread. Friction in the bit holder, in the joint and under the head are not in the reading, so a clutch setting taken on the bench and a joint torque measured on the line are different quantities even when the numbers look comparable.

For a screw that is already tightened, this is not the instrument: measuring the torque needed to loosen it requires an in-line detector at the bit, not a reaction head under the tool. And for a tool whose output is a series of impacts rather than a continuous drive, the peak of the first blow is not the working torque, so an impact tester is the right choice.