DIY Multi-Turn Potentiometer (Using Worm Gear Mechanism)

We tinkerers have used potentiometers whether it is of a buck-boost converter or simple audio amplifier, and at some point, we struggled with controlling it precisely.

We can get trim pots but setting those regularly is not so easy. Also, there are multi-turn potentiometers available in the market but they are generally expensive and only available in a limited range of values.

So in this Instructable, I will show you how I made a simple mechanism that can be used to turn any potentiometer into a multi-turn potentiometer.

For this project, you only need two things and some 3D Printed Parts

1. Any potentiometer(diameter 15mm)
2. 2mm Diameter pin (25mm length)

Access to a 3D printer is required.

The device which we are going to build will be working on the principle of the worm gear mechanism.

In the worm gear, there are two parts, one is a worm wheel and the other part is the worm gear.

As can be seen in the animation above when the knob is rotated, the worm gear rotates which rotates the worm wheel and thus the potentiometer shaft rotates.

The benefit of the worm gear is that it can provide very high gear reduction in a very small space, but it comes with a drawback that it can't be back driven means the worm wheel can't rotate the worm gear. In our case, this drawback doesn't harm us.

The designing of the enclosure for the gears and the potentiometer is done in Autocad Fusion 360.

To make the gears I have utilized the script functionality of the Fusion 360.

I have utilized GF GEAR GENERATOR Add-on to do so. You can get it from the Fusion 360's Add-ons store.

I have chosen 1:15 reduction which means for every 15 turns of worm gear the worm wheel will rotate 360 degrees, but the potentiometer only rotates 300 degrees so the number of rotates on worm gear translates to full rotates of potentiometer turns out to be 12 rotations which will provide enough precision of the given range.

After the design is done we can move forward to 3D Print the gears and covers.

The 3D STL Files are given below and you can 3D Print the same if you want the same gear ratio.

I have also provided the STEP file if you wish to tweak the paramters.

All the files are printed in PLA with two perimeter walls and 15% infill.

There will be few bridges and most of the 3D printers can handle it very easily.

This is the assembly guide for reference purpose.

First, take the main body and insert the potentiometer into the cover and mind the direction of the potentiometer, there will a slight indent on one side which will be inserted in the small hole on the bottom of the main body along with the hole for the potentiometer shaft.

After inserting the potentiometer lock it in place with the help of the nut that comes with it from the top of the cover.

Now we need to insert the gears into their place.

First insert the worm wheel(gear with the D hole) into the potentiometer, then insert the worm gear into its place.

If the worm gear is fitting rigidly into the body, then first sand it using some sand paper or file.

To lock the gears and provide a shaft to rotate them we will insert pins into the worm gear, I have chosen two pins as one pin was getting loose after a while.
Yes, I could have used some sort of glue to fix the shaft but I tried to avoid glue for this project and made everything mechanically assemblable.

Two pins will not rotate on their own axis rather they will help in rotating the gear.

To easily rotate the gears we will attach a knob that will slide into those two pins we have attached in the last step.

Before covering it up, rotate the knob so any kind of friction is removed between the gears.

The top cover will be friction fit on the main body, just align it and press it into the main body and it will stay there due to friction in between the parts.

The friction fit highly depends on the tolerances of the 3D printer. If you face difficulty in inserting it, you can reprint it with a slightly scale downed version.

Woohoo! now you can convert any potentiometer laying around into a multi-turn potentiometer and enjoy the precision in your hands.

If you face and difficulties or want to give any suggestions then comment below.