Spring Turning Machine

Who doesn't like springs? Nice elastic members which can give force when required or store mechanical energy for you. They are pretty simple yet amazing.

But when it comes to buying springs, it is not at all an easy task. Especially if you are looking for springs in small numbers and/or you are on a budget. I had previously made an apparatus to check the spring constant. In this instructable, I have shared how I made a spring bending machine.

This machine can create a spring with any diameter that you would like with any number of turns. It is a bit different than the machines shown for hobby use created by our friends like Jiri Praus. One of the major cons with his machine was that it required two stepper motors, stepper drivers and micro controllers. While I am comfortable using stepper motors and micro-controllers, I wanted to make a machine without them to keep the cost low. My machine resembles the process used to manufacture springs in large numbers. A wire is forcefully extruded through a hole and it is forced onto a roller or a metal wedge which bends it as soon as it exits the hole.

An example of an industrial spring bending machine : https://youtube.com/shorts/hcPpGqRGLns?si=_lwNsoc-Zq_TyFtI

I used the following materials to make my machine. Off course, for the 3D printed parts, they can be ordered with widely available 3D printing services online. I have attached the fusion 360 file for the machine and you may download and edit the same to suit your taste.

1. 3D printer
2. Geared DC motor
3. Box cutters
4. M3 Bolts
5. M3 Nuts
6. M3 Taps
7. M8 Nuts
8. M8 Hex head bolts
9. Metal wire

I have attached the fusion 360 file for the machine in this step. Please feel free to download and modify the file as per your convenience and also let me know so that I can incorporate the change on this page as well.

Since instructables does not support .obj extension, I have attached the file in my google drive.

You may download the file at:

https://drive.google.com/file/d/1Bzmv6zLibTKpQSSoWRui6tJ62_vyxufp/view?usp=drive_link

Like in the industrial version, my machine also has a nozzle through which the wire is extruded. Just after coming out of the nozzle, the wire is forced on to a ball bearing. This bearing forces it to deflect. This deflection causes the wire to coil and turns the wire into a spring.

This mechanism has no control over pitch of the coil. The pitch is essentially just half of the thickness of the nozzle. However, it is not a very big concern as we can pull the springs if we need the pitch to be higher.

In my view, the gripper is by far the most complicated of all the components of the machine. It is important that this gripper grabs the wire hard enough to push it against the heavy force required to coil the wire.

The gripper, like all other parts of the machine, is 3D printed. The hardness of the plastic is much lower than that of the wire. It simply cannot grip the wire tight enough to be pushed against large force of bending the wire.

To solve this issue, I have created slots to add box cutter blades in the slots to grip the wire. When the force is put on the extruder, the force is transferred on the wire which in turn helps the blades grip wire better. To fine adjust the protrusion of the blade, there is a bolt at the back of the blade. When the bolt is tightened, the blade would be pushed on to the wire.

I have also attached a clip of assembly of the gripper mechanism in two parts. The first part is the assembly of the blade in an individual arm, and the second one is the assembly of both the arm to form the gripper mechanism.

The third clip is just shows the addition of the guiding bolts to the mechanism.

The gripper also has such a structure that it can only push the wire towards the nozzle. During the return stroke, the wedge opens and does not pull the wire back. The one way action is also ensured by the resistance of the wire straightener and the obstruction created by the already wound turns in front of the assembly.

There any many options to choose from when it comes comes to generating the force to coil the spring.

But I went with a lead screw coupled directly to the motor shaft. In my case, the lead screw and nut are nothing but a standard hex head M8 bolt and nut. The motor is a simple geared DC motor which is rated at 180 RPM at 12V. The pitch of the screw is 1.25 mm.

Thus, at 180 rpm (3 rev/second), the extruder will move at 3.75 mm/s.

I also choose a hex head bolt because it is easier to lock the bolt head with a hexagonal cavity in the coupler.

It is important that the machine should be able to make springs of any diameter. This is achieved by adjusting the horizontal distance between the centre of the bearing and the nozzle.

In the drawing image, the distance between the nozzle and the axis of the bearing is smaller than in the image on the right. When the distance between the bearing and the nozzle is lower, the spring has to wind itself in a small space and the diameter of the resulting spring is smaller.

If the distance between the nozzle and the bearing axis is increased by adjusting the nozzle position in the slots, the resulting spring would be with larger diameter.

The wire straightener is added as an after thought. The main problem was not the bends in the wire, but the twist that the wire was taking.

It was necessary to have some constraint so the the wire wouldn't twist. And hence I added the wire straightener.

The straighter presses the wire heavily from both sides. This grips the wire tight enough so that it cannot twist.

I have also attached a clip of an industrial wire straightener

The electric circuit is based on an RS Latch circuit. The limit switches on the either side change the direction of the motor.

When the forward limit switch is hit, the circuit lathes the motor in reverse mode, and when the reverse limit switch is hit, the motor enters the forward mode. This gives the system the oscillating nature which allows the machine to churn out springs continuously.

The circuit diagram of the system is shown in the image of this step. The relays used here were 12V ones.

When the machine is powered on, one of the sides of the RS latch turns on randomly. This sets the machine in motion either in forward or reverse direction. Once the machine is in motion and hits the limit switch on the either side, the motion is reversed the machine continues this back and forth cycle indefinitely.

The circuit also has a capacitor bank. This bank ensures that there is enough power available to latch the relays at all times. This is especially important when the motor switches direction. This circuit does not have a soft start of any sort. Hence, when the motor voltage is flipped, the current inrush is huge. This will definitely cause the supply voltage to collapse and more so if the system is powered by a switching mode power supply.