Description

A 2L (1 gallon) garden sprayer half filled with water based coolant (10% oil, 90% water) supplies coolant to the injector at a low pressure. A micro computer (ESP32-C3) sends pulses to a solid state relay that is connected to the 12V fuel injector coil. At every pulse, the fuel injector sprays a bit of lubrication. Due to the low pressure, typically far less than 1 bar, the drops are relatively large and the risk on aerosols is minimal.

An OLED display and rotary encoder with push button are used to activate the injector and set the pulse rate. A Mist and Coolant input (3..24V, CNC controller) can also start/stop the injector. The system can run without display and/or rotary encoder.
There is no need to use the micro computer. Any pulse signal that can drive a SSR will do. This makes it possible to drive the relay directly by the CNC controller.

Typical pulse conditions are 5Hz and 2 millisecond pulse time. That results in a very low amount of lubrication, just a few drops a minute. Under these conditions, I run 50 hours without re pressuring the garden sprayer and the half filled tank is good for 100 hours run time.

I used a 12 volt fuel injector from a small European car (citroen C3) that has a 4 cylinder petrol engine. This fuel injector can be bought cheap (10 €) on Chinese web shops.

Currently the system is used on my lathe and I am very happy with it. I also want to use it on my CNC router to make a mist coolant system. For that the PCB has a relay output to connect an air valve. The mist / air coolant mode is only bench tested. As soon I have the time, I will adapt my CNC router for mist / air coolant.