[UKRobotics]

I was having a good look at the pneumatic system on my bridgeport interact yesterday to try and suss how everything works and whilst most of it seems reasonably self explanitory, the drawbar mechanism has left me rather confused.

Unfortunatly I dont have any photos because my camera packed up but I'll try to explain as best as I can. From the air inlet there are a variety of filters and resivoirs which I assume are either to add or remove oil/dirt/water from the air, it then goes to some splitters so it can be distributed to different parts of the machine.

Once pipe is for the drawbar. This goes via a solonoid valve to a large cylinder shaped object at the base of the mill but I dont have a clue what it is. It looks almost like a hydraulic/gas ram but with no moving parts.

Written on it is
Spencer Franklin Booster
Max Inlet Pressure: 120 psi
Intensification ratio: 25:1

So what does this thing do ? It is just a simple buffer/expansion tank to ensure there is always a high enough flow rate to run the draw bar at the right speed or is it somthing more complicated than that ?

I also need to somehow find out how all the sensors in the drawbar mechanism worked on the original controls so I can build the appropriate logic into my retrofit to make use of them. There are about 5 microswitches and another module which I couldnt identify for certain but it looks a lot like a proximity sensor.

[machintek]

It sounds like you have an Interact 4. This had a hydraulic cylinder up top to push on the drawbar. Because this may need in excess of 1500 pounds of force they use a air amplifier to push on a master cylinder at the base of the machine. Very similar to how a hydraulic jack works. It gives you a calculated mechanical advantage. The air cylinder has a certain diameter working with so much air pressure. It works against a hydraulic cylinder. The ratio is 25 to 1. Thus if you put 100 PSI into the cylinder, it produces a force of 2500 psi at the hydraulic cylinder. I have used a similar contraption to fill 3000 PSI scuba tanks from a 2000 PSI source (and 4000 PSI paintball tanks from a 120 PSI source). It all depends upon the ratio of the amplifier.
I have had problems on the earliest Interact with leaks and being trapped in the cylinder. This consumes a certain amount of the capacity of the system to compress the trapped air and may not have enough stroke to release the tool.

George

[UKRobotics]

Wow thanks, that makes a lot of sense. As I was poking arround it did cross my mind that the pipe leading up top looked very much like a hydraulic pipe, but considering that most of the power and signal cables are routed though what looks like hydraulic pipe I didn't give it any further thought.

The next step of course is to sort out the electrical side of it. I have removed all the old electronics to be replaced with my own new system based arround rutex drives and mach 3. Theres a whole load of sensors and switches arround the drawbar area which I assume are to ensure that the quil is in the right place before the solonoid valve can be fired.

Having never had the oppertunity to use a machine with a power drawbar I'm at a bit of a loss as to what is 'right'. It wouldnt be difficult to make up a simple logic circuit using transistors or relays to ensure that the switches/sensors are obeyed, but I dont know what conditions I should be allowing at what point , and what not to.

How does the drawbar work anyway? It appears that the small hydraulic ram fires down on a shaft causing it to release the tool, but what holds the in ? Is it just a spring ?