10 turn potentiometer counter knob

Please note this model has been designed for and tested with a 0.25 mm nozzle. It contains small, precise mechanical elements and text that greatly benefit from smaller diameter nozzle. While it should be possible to print it with a standard 0.4 mm nozzle, some adjustments may be necessary and the overall print quality, mechanical operation as well as fit and finish may suffer.

A knob for a 10-turn potentiometer of the Bourns 3590 series* (or compatible) type. It contains a planetary gearset that drives a turn counter disc with a 11.11:1 ratio in relation to the knob position. While technically not a Vernier scale, it serves a similar purpose where the two scales allow for a semi-precise indication of the number of turns and the position within a turn.

Sadly, it does not go up to 11. If there's sufficient interest, a special Nigel Tufnel edition will be considered.

Non-printed hardware needed

You will need two M2 x 6 mm screws with cylinder head. I used ones with Torx T6 head.

Printing

Please note this model relies on a well-calibrated printer and assumes an accurately tuned first layer for details like gears and number features. If you're only just beginning I would kindly suggest getting some experience with less detailed/demanding prints first and only then trying out this model, once you're confident that your printer is set up as well as possible.

As mentioned at the beginning, this model is meant for printing with 0.25 mm nozzle. I personally use E3D Revo Six hotend. All the Prusa i3MK3 G-Codes are sliced for 0.25 nozzle and MK3 files use this size by default as well. Of course you're free to slice the files however you like it if you only have a default 0.4 mm nozzle but please keep in mind that some experimentation and tuning might be necessary in that case and the quality of the model, especially numbers and gears, will suffer.

Besides 0.25 nozzle, 0.1 mm layer height and PLA material is recommended.

Base, sun and gears

Smooth PEI-coated steel sheet recommended for a good adhesion of small elements like the sun gear with knob stem and compound gears. A well-cleaned sheet surface is a must. Try using brims if small elements keep dislodging.

Number disc with ring gear

Satin steel sheet is recommended for classy looks but a smooth one will do as well. There is a filament color change programmed in after the first layer in the 3mf  and gcode file. Start with a desired counter disc background color (black in the example photo) and then continue with desired counter disc number color (white in the example photo).

Cover

As with the number disc, a satin sheet is recommended for the best surface aesthetics but use the smooth one if that's all you have. A color change is programmed in the 3mf and gcode file before the 4th and the 6th layer. The idea is to start with the same color you've done the base in, then change to the cover number color (black in the example photo) and then change back to the base color after two layers and continue with that to the end.

Knob

The steel sheet texture is mostly irrelevant with this one. Two color changes are programmed-in in the 3mf and gcode file so we start with an accent color (red in the example make), continue with your color of choice for the knurled part (same as the base color in the example) and finish off with the accent color again, so the contrasting indicator line at the top shows through.

Spacer

A distance of 3.5 mm is required between the surface of the potentiometer case and the base of the knob case. For instance, if the thickness of the sheet metalwork of the device you intend to mount the knob on is 1.5 mm, you'll need a (3.5 mm - 1.5 mm) = 2 mm of spacer height. Three different spacer models are provided with 0.5, 1 and 2 mm heights so you're free to mix and match until the desired distance is reached but it's best just to scale the single one up- or down to the required height by the Z axis in the slicer program.

Assembly

1. Make sure the two screw holes in the base are clean and smooth. Put an M2 screw in each of them and make sure it turns freely. Put the screw in and out repeatedly if needed, until there's no significant friction.
    
2. Take a compound gear and screw the M2 screw in from the larger cog side all the way until its end is flush with the small cog's surface. As we're screwing the machine screw into the plastic here, this procedure ensures the thread in the gear gets created nice and straight. Unscrew the screw. Repeat with the second compound gear.
    
3. Screw the first compound gear, the one that sits lower, into the base. The larger cog has to face the back of the base. The screw head goes into the back of the knob base. Screw it in all the way carefully and then back off half a turn or so until the gear spins freely but there's not much up-down play. Repeat points 1-2 if needed. Repeat with the second compound gear that sits higher. It should engage with the first one so when you turn the first (lower) one, the second one also spins freely but slower.
    
4. Put the washer and nut that came with the potentiometer over the hole in the base. Put the base over the potentiometer mounted in the target device with the spacer attached, careful not to damage the compound gears. Secure the base in place by tightening the nut against the washer with needle nose pliers. Make sure the gears still spin freely and nothing rubs. Adjust the spacer height if needed.
    
5. Make sure the potentiometer is at its counter-clockwise limit position. Insert the sun gear with knob stem over the potentiometer shaft. Rotate the printed part counter-clockwise and simultaneously carefully push it in until it engages with the compound gear. Keep turning counter-clockwise and pushing in until the  in the printed part locks with the ridge in the potentiometer shaft. Make sure the sun gear engages with the compound gears and everything turns smoothly. Use a narrow piece of Kapton tape between the pot shaft and the knob stem if the latter moves too freely over the former. Move the potentiometer back to its counter-clockwise limit position afterwards.
    
6. Put the number disc with ring gear over the sun gear with knob stem so the “0” falls in the middle of the top arc that protrudes inwards from the base. It should engage with the smaller cog of the higher-sitting compound gear.
    
7. Put the cover over the base. It should snap into place with the help of the four small protrusions over the circumference of the cover.
    
8. Put the knob on the sun gear with knob stem so the indicator points at “0” imprinted into the cover.

*) If you've verified the model is compatible with another type of pot without modifications, please let me know so I could update the description. Thanks!