Re: [CAD_CAM_EDM_DRO] Bridgeport Milling Machines

info.host@... wrote:

> > Yes, the hydraulic tracer mills are more trouble, as they have
> > hydraulic cylinders instead of leadscrew. on the other hand,
> > they may go so cheap that it eases the pain.
>
> Hydraulic ones make a nice humming noise too, but that's not really too
> important I don't think. I asked a guy selling one who said when they had it
> put in it was accurate to 0.001" or around there. I was thinking if there
> would actually be a way to use a hydraulic mill for CNC.

Sure. 30+ years ago, there were a number of hydraulically operated
CNC machines. they generally ate their owners alive in maintenance
cost! That's why electronic servo systems are king today, because
the cost of ownership is vastly less. Now, they are getting rid of
hydraulics on aircraft, as they can do many things more reliably
that with hydraulics.

> I am working on a
> few things I'm not overly sure of which is probably where my downfall is;
> that the tracer probe feeds a low pressure into the pump. My 'plan' was that
> you could remove the tracer head and all the bits that measure the piece,
> the controls. Then take a block of aluminium and bore cylinders into it. At
> one end of the cylinder you reconnect the hose and the other you have a
> piston. The piston's advance and retreat is controlled by motor so it can be
> CNC'erised. The problem would be in finding the working pressure that the
> tracer feeds to the pump and then working out piston sizes, belt sizes and
> motor sizes to supply the pressure. I have no idea if it'd work but it just
> seems something that seems so useless to us has to be hiding something.

I really don't think this is a practical solution at all. A much better way is

to replace the tracer valve with separate proportional hydraulic control
valves, commonly called Moog valves. Be sitting own when you inquire
about the cost of these valves. They go for thousands of dollars each!
These valves have millisecond response, extremely small deadband, and
a very linear relationship between current in the coils and flow to the
cylinder. Your proposed lashup would not be able to come close to a
properly set up proportional servo valve. The motors would have so much lag
that the system would be hunting .01" all the time. The working pressure
in these systems (and in the tracer-valve systems, too) is probably between
1000 and 1500 PSI.

Jon