Power drawbar - controller box thing

I dug out the original power drawbar controller. This is a single-sided PCB in a steel box that was mounted on the side of the ram housing. The impact driver was wired into it, as was the pneumatic solenoid that engages the impact driver with the splined end of the drawbar.

On the board are a couple of 240V relays and a 400V SCR. Apart from the 240V supply / fuse / toggle on-off switch on the supply side plus the aforementioned impact driver and solenoid, the only external connections are 3 wires that used to connect to the contacts of a couple of relays in the old control box. Everything on the PCB is at mains potential, so there will need to be additional relays between the CNC controller and this box if I keep it.

There are 2 primary functions you'd expect from a simple drawbar controller - control of the impact driver direction (including powering it on and off) and activating the solenoid. On a good day you'd also ensure there was a delay between the solenoid engaging and the impact driver starting to turn, to avoid nadgering the splines. On an even better day you'd actually use a microswitch to detect that the driver is actually fully engaged with the splines before powering the driver but that would make things more complex than strictly necessary.

With 3 wires and 2 functions, one of which is connected directly to neutral, it's pretty clear that one of the remaining 2 wires represents "on - off" and the other sets the direction. And the components on the PCB are primarily for a time delay circuit that drives the impact driver through the SCR. I wired up a dual changeover light switch to test it quickly, with the solenoid and driver lashed up. Turns out that the second relay wasn't connected to anything on this system.

Well it worked - but it had to really didn't it? There's not much choice in the matter when you only have 2 inputs and 2 required functions and it was working when last connected apparently.

I reckon I'll just wire it up on the machine for now. I don't have any compressed air so it won't work for now unless I manually engage the driver with the drawbar. But hopefully I will have a fix for that soon. 

Required for final operation: 

• "Tool in" and "Tool out" push buttons, ideally 240V, to avoid need for yet more relays.
• Interlock with VFD, perhaps using a "spindle stopped" output to control a (solid state?) relay preventing drawbar operation until the spindle is stopped. 
• Possibly a means of engaging the electric spindle brake during tool change.

These are the functions you can assign to the 3 multifunction output terminals of the Yaskawa V1000 VFDs:

In particular, the zero speed function would be quite handy:

This could be used to directly drive a SSR that powered the power drawbar circuit - or its enable signal. Then the drawbar could be prevented from trying to operate unless the spindle were stationary. I could further enhance the safety factor by running said signal through a microswitch detecting if the quill was at the top (tool change) position. Then the drawbar will only attempt to operate if the quill is at top of travel AND the spindle is stopped. Given that I have 3 switches at the top of travel (one is currently used for limit, one is used for dead stop), there is one spare that could be used for this purpose. Sounds like a plan, particularly if I fit the (tiny) SSR into the original drawbar controller box...