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. That makes it possible to drive the relay using only a CNC controller.

Typical pulse conditions are 5Hz and 1 millisecond pulse time. That results in a very low amount of lubrication, just a few drops a minute.
I used a 12 volt fuel injector from a small European car (citroen C3) that has a 4 cylinder petrol enggine. 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 coolant mode is only bench tested. As soon I have the time, I will adapt my CNC router for mist coolant.