Adding an Axis for coolant dosing to post processor

[Max.Borhof]

On my CNC I use a stepper motor peristaltic pump to dose the coolant in a Fogbuster-style minimal lubrication system. Until now, the stepper is driven by an external controller with a potentiometer to manually adjust the speed of the stepper motor. While it makes coolant dosing more reliable than the original Fogbuster, I still have to constantly adjust the stepper speed for different tools and their respective cutting speeds.

In a first step, I would like to add another axis to my CNC-controller to drive the peristaltic pump. My goal is to regulate the amount of dispensed coolant via Gcode.

I was hoping for the G-Code wizards to lend a hand or point me in the right direction.

Right now I am using an almost unmodified version of the Autodesk Reprap Postprocessor

[thePostmaster]

What's does the line of code that controls the flow look like? It should be pretty straight forward to add in a line that references the feed speed. Could be done at every feed speed change. 

[Max.Borhof]

@thePostmaster 

Referencing the feed speed is a great idea!

For now, I have just set up an additional Axis W for the pump motor. I can easily adjust the coolant flow by changing the steps per millimeter for the W Axis on the controller side. So for example if I command the W-Axis to move 100mm (G1 W100) it would dispense 100ml of coolant. 

So a straight cut in X+ direction would look something like this:

G1 X100 W2000 F2000

It would be nice if the W-axis is only progressed on feed moves (G1, G2 and G3) moves and not on rapid moves (G0).

I have already set up a tool change macro that adjusts the steps/mm of the coolant Axis depending on the tool diameter, so that tools with a larger diameter get more coolant than smaller tools.

EDIT: Maybe it would make even more sense to ajust coolant flow depending on the cutting speed of the tool?

[Max.Borhof]

"Push"