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Lathe electronic leadscrew controller

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Clough42 Lathe Electronic Leadscrew Controller

This is the firmware for an experimental lathe electronic leadscrew controller. The goal is to replace the change gears or gearbox on a metalworking lathe with a stepper motor controlled electronically based on an encoder on the lathe spindle. The electronic controller allows setting different virtual gear ratios for feeds and threading.

Silkscreened Control Panel

Latest Version

The latest version of the firmware has been updated with several new features and fixes: * Fix phantom control panel button presses * Add power button support * Fix integer overflow for large metric threads * Prevent mode and direction changes while running * Smooth tachometer display * Add support for lathes with separate feed and thread gearing


Project Status


NOTE: This is still a work in progress and is subject to change. Hundreds of people all over the world have purchased parts and are following along with the build. That's great! I have had great success with mine, as have others. Building an ELS for your lathe does require require basic electronics and troubleshooting skills, so keep that in mind if you decide to build one yourself.


For documentation, please VISIT THE PROJECT WIKI.


The project is still in active development. The current hardware looks like this: * Use a TI F280049C Piccolo microcontroller on a LaunchXL prototyping board * Use an inexpensive SPI "LED&Key" import display and keypad for the user interface * Read the spindle position using a rotary encoder with a 3D-printed gear or belt drive * Use a standard stepper motor (or servo) and driver on the lathe leadscrew * Make as few modifications to the lathe as possible: * Use the original leadscrew and halfnuts without machining * Drive the leadscrew through the factory input shaft * Drive the encoder from the factory spindle gear train * Make it easy to restore the lathe to the original change gear configuration

The ELS firmware currently supports the following: * Feeds in thousandths of an inch per revolution * Feeds in hundredths of a millimeter per revolution * Imperial thread pitches (in threads-per-inch) * Metric thread pitches (in millimeters) * Imperial and Metric lead screws

Items on the short list for future development: * Support for dual-shaft lathes that have different drive ratios for feeding and threading * Support for powering down the leadscrew while leaving the tachometer active * Leadscrew speed limit warnings * Tachometer averaging (stabilization)

Possible Future Goals

While this project is starting out as a simple gearbox replacement, some features seem attractive, even for that simple case: * Threading/feeding up to a hard shoulder with automatic stop * Automatic recall and resync with hybrid threads (e.g. metric threads on an imperial leadscrew)


This is not a CNC project. The goal is not to control the lathe automatically, but rather to transparently replace the lathe change gears or quick-change gearbox with an electronic virtual gearbox that can be quickly set to almost any ratio. The lathe will continue to operate normally, with the operator closing and opening the half-nuts to control feeding and threading.

Hardware Configuration

If you want to get this running on your own LaunchXL-F280049C board, here are the settings you will need:

Physical Switches

The LaunchXL-F280049C has a number of switches on the board to configure the GPIO and peripheral signal routing. This provides lots of flexibility for different uses of the board, but it means that you will have to change some of the switches from their defaults in order to use the GPIO pins and eQEP periperals.

These are the required switch settings *

S3.1 = 0
Connects eQEP1 to J12 *
S3.2 = 0
Connects eQEP2 to J13 *
S4 = 1
Connects eQEP1 to J12 *
S9 = 1
(default) -- Connects GPIO32/33 to BoosterPack site 2 pins

S6 and S8 can be in any position. 0 is the default.

External Connections

The firmware assumes the following pins are connected externally.

NOTE: the silkscreen on the LaunchXL-F280049C board has the labels for J6 and J8 swapped. J6 is the header closest to the edge of the board.


A quadrature encoder for the spindle is connected to the eQEP connector, J12.

Stepper Driver

A Step-direction stepper motor driver should be connected to the following GPIO pins: *

(J8 pin 80) - Step *
(J8 pin 79) - Direction *
(J8 pin 78) - Enable *
(J8 pin 77) - Alarm input

Control Panel

The LED&KEY control panel board must be connected through a bidirectional level converter, since it is a 5V device, and the TI microcontroller is a 3.3V device. A standard BSS138-based converter works well. *

(J6 pin 55) - DIO *
(J8 pin 71) - CLK *
(J6 pin 53) - STB (chip select)

Debugging Outputs

In addition to the control wires for the hardware, the firmware also outputs signals on two additional GPIO pins to allow timing of the interrupt and loop routines. An oscilloscope or logic analyzer may be connected to these pins to debug and time the ISR routines: *

(J8 pin 76) - Main state machine ISR *
(J8 pin 75) - Secondary control panel loop

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