# Optical encoder disc Ø60, 30 slots, Ø5 bore

> How many slots for an RPM encoder disc, and what size?

- Category: Stirling engines › Generators & instruments
- Kind: Hardware
- Basis: Slotted disc for a transmissive IR slot sensor (TCST2103, 3.1 mm gap): Ø60 × 1.5, 30 slots on a 48 mm circle, Ø5 bore
- Page: https://xemstudio.com/objects/encoder-disc/ · JSON: https://xemstudio.com/api/geometry?object=encoder-disc · Plain text: https://xemstudio.com/objects/encoder-disc/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- The disc is Ø60 × 1.5 mm with a Ø5 bore for a Ø5 shaft.
- It has 30 radial slots, each 2 mm wide × 6 mm long, centred on a Ø48 circle (from r 21 to r 27), 12° apart: 30 pulses per revolution.
- At 1.5 mm thick it passes through the 3.1 mm gap of a TCST2103-type IR slot sensor.
- Rpm = pulses per second × 60 / 30.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| encoder bore | Ø5 | Ø5 shaft | slide | encoder-disc-* |
| encoder slots | 30 × 2 wide × 6 radial | IR slot sensor (3.1 gap) | designed | encoder-disc-* |

## Sizes

| feature | size |
|---|---|
| disc | Ø60 × 1.5 |
| bore | Ø5 |
| slots | 30 × 2 wide × 6 radial |
| slot circle | Ø48 |
| pitch | 12° |

## Where the files are

- Wikipedia: [Thermocouple](https://en.wikipedia.org/wiki/Thermocouple) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Hall effect sensor](https://en.wikipedia.org/wiki/Hall_effect_sensor) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Dial indicator](https://en.wikipedia.org/wiki/Dial_indicator) — web — CC BY-SA 4.0 (text)
- Analog Devices: [DS18B20 datasheet](https://www.analog.com/en/products/ds18b20.html) — PDF — Manufacturer datasheet
- Long Earth Society: [Engine and rig builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/encoder-disc/index.json

- encoder-disc-30-slots-60mm: [STEP](https://xemstudio.com/files/hardware/instrument-mounts/encoder-disc-30-slots-60mm.step) · [STL](https://xemstudio.com/files/hardware/instrument-mounts/encoder-disc-30-slots-60mm.stl) — optical encoder disc Ø60 × 1.5, 30 slots 2 wide × 6 radial on a 48 mm circle, Ø5 bore (for an IR slot sensor)

## How it fits

### Goes in or on
- [Metric shafts Ø3 to Ø10 with D-flats and clip grooves](https://xemstudio.com/objects/metric-shafts/): Ø5 bore on a Ø5 shaft (slide)

### Alternatives
- [Hall sensor mount for TO-92S (A3144 / SS49E)](https://xemstudio.com/objects/hall-sensor-mount/): magnetic pickup instead of optical

## Questions

**How do I measure RPM with an encoder disc?**

Count slot pulses from the IR slot sensor: rpm = pulses per second × 60 / 30 for this 30-slot disc.

**Will a 1.5 mm disc fit an IR slot sensor?**

Yes; the TCST2103 gap is 3.1 mm.

## Fits with

- [Hall sensor mount for TO-92S (A3144 / SS49E)](https://xemstudio.com/objects/hall-sensor-mount/)
- [Split probe clamps for Ø3, Ø4.8, Ø6 probes and Ø8 / Ø9.53 dial-indicator stems](https://xemstudio.com/objects/probe-clamps/)
- [Metric shafts Ø3 to Ø10 with D-flats and clip grooves](https://xemstudio.com/objects/metric-shafts/)
- [Crank discs for a Ø5 shaft, 10 to 30 mm stroke](https://xemstudio.com/objects/crank-discs-5mm-bore/)