It's not unusual for someone new to precision fastening to complain about the lack of precision of electric screwdrivers when dealing with hard joints; in reality, a smart fastening system with torque control like Kolver's K-DUCER can be easily programmed to achieve superior precision even with the hardest joints.
As we have seen before, a hard joint is characterized by minimal movement between the mating surfaces during tightening, resulting in a rapid increase in torque once the fastener makes contact. This abrupt torque rise can lead to over-tightening, potential damage to components, or inconsistent clamping forces when working at too high of a speed, due to the inertia of all the rotating parts.

The K-DUCER addresses this challenge through its downshift function.
This feature allows the screwdriver to operate at a higher speed during the initial rundown phase and then automatically reduce speed upon reaching a specified torque threshold. By slowing down as the torque increases, the downshift function provides operators with greater control during the critical final tightening stage, ensuring the desired torque is achieved without overshooting.

Furthermore, starting with v40, the K-DUCER will automatically detect when the operator is working with a hard joint and not using the downshift function, and recommend that the user take action in changing the tightening strategy.

When and why are hard joints used?

Hard joints offer durability, strength, and precision, making them ideal for applications with high force, vibrations, and extreme conditions. Their rigidity ensures long-lasting connections with minimal risk of untightening and less maintenance due to their resistance to wear and loosening. This makes them a popular choice in automotive and aerospace industries, and occasionally in electronics, typically in situations where vibration could damage the component. 

A Practical Example

Let's set up a test environment with a metal-on-metal joint and a brand new K-DUCER system.

Our testing environment.


For our initial rundown, let's set the screwdriver to 600 RPMs, the torque target to 3.50 Nm, and observe what happens.



Our initial settings.


Our initial results.

As we can see, at that speed, the screwdriver had so much inertia and so little time to stop that it overshot the target torque by almost 1.50 Nm. Looking at the torque vs. angle function graph, we can see how this hard joint has a very steep slope and the angle from the seating point to the final torque is quite small. In other words, there is a very small interval between when the screw makes contact with the underlying surface and when the screwdriver reaches the final torque and has to stop.



The torque-angle function rises steeply after the screw is seated.

Inevitably, this becomes impossible to do at high speeds, just like trying to stop a moving vehicle traveling very fast.

More technically, during the run-down phase, the screw rotates quickly and freely because there’s little resistance. As soon as the screw head touches the surface (the seating point), resistance spikes instantly because there is very little material compression or flex. The sudden stop in screw rotation (due to resistance) means that any remaining kinetic energy from the high-speed motion gets absorbed as extra torque.

Setting Up the Downshift Function on the KDU Controller

Now let’s go back to the Torque & Angle screen of our program’s settings and enable the downshift function.


Downshift turned ON.

After turning downshift ON, let’s leave our initial speed to 600 RPMs but set a final speed of 75 RPMs starting at 0.50 Nm, i.e., shortly after the seating point.
Shortcut: when prompted on whether to save your changes, press & hold YES to go straight back to the main screen.

Let’s see what happens now…


Our much improved results.

The screwdriver now approaches at the same speed as before but noticeably slows down right as the screw is seated. There is now no overshoot, and we can see that the achieved torque is 3.51 Nm, right on target!

Our downshift function operated as intended, providing precise torque control for our hard metal-on-metal joint.

Pay close attention to your tightening settings

Summarizing, when fastening hard joints at high speeds, the screwdriver’s inertia and motor response time can cause the tool to apply more torque than intended before it can stop, potentially leading to over-tightening, thread stripping, or even fastener failure. It will also likely make torque readings inconsistent, with high variability from one tightening to the next, affecting quality control.

By reducing the screwdriver’s speed just around the screw’s seating point, the tool has less kinetic energy to absorb and will stop more precisely at the target torque.

The K-DUCER will now alert operators if they’re dealing with a hard joint and haven’t accounted for that in their tightening strategy so that they can take the simple, necessary steps to get a more controlled tightening process and ensure a repeatable, high-quality fastening.

If you need help with a challenging application, you can reach out to our team anytime at [email protected]