Re: SV: [CAD_CAM_EDM_DRO] CNCing a big surface grinder ?

Anders Blix wrote:

>>>Alternately, what's the feasibility of spending a few bucks on
>>>electrical hydraulic valves? You'd still need some form of
>>>
>>>
>>encoder for
>>
>>
>>>positional feedback, but no need to tear into the treadmills.
>>>
>>>
>>>
>>>
>>Ugh! A bad choice. Back in the relatively early days of CNC, many
>>machines were made with hydraulic motors for brute force, and
>>proportional servo valves as the amplifiers. This required a
>>hydraulic
>>pump running into a pressure relief valve, so that the system drew
>>maximum electrical power all the time, and dissipated the heat from
>>the fluid in big coolers. (Why they didn't use variable-displacement
>>pumps, I don't know.) The noise, power consumption and maintenance
>>headaches were huge, and as soon as power electronics got to the point
>>that large electric motors could be controlled with electronic servo
>>amps, all these machines were retrofitted or scrapped.
>>
>>
>
>This was very useful information for me! I'm looking at buying an old VMC for retrofitting with EMC or other computerized control. The ting then would be to avoid the hydraulic ones. How do I know which ones are hydraulic????
>

Well, actually, you might get a good deal on a hydraulically-driven machine
with leadscrews. Get rid of all the hydraulics, replace with DC electric
motors and modern electronics. Which are which? Well, a Moog Hydrapoint
is certainly hydraulic, and some old Cincinnatti machines are, too. You
likely can tell from the pictures, by the obvious hydraulic hoses and metal
lines, or the hydraulic power unit, a big tank with a 25 Hp motor in the
bottom, with what looks like a car radiator on the side. (This could
possibly
be confused with a spindle cooler in some pictures.)

> It's not always that easy to know on many of the ones offered on ebay. But generally what type of controller it have is mentioned. I assume it is possible to find out what drive system is used by looking at the controller system?
>
>

Not for sure. Many of the mid-70's controls could run hydraulic or DC servo
with the switch of one card. I know the Allen-Bradley 7320 supported both.

>I tried to find out by looking at Fanuc WebPages to se if they had any info on the different older systems. But the only thing I found there is info about all the fancy new ones. No info on older systems. Does anyone here have info about this???
>
>At about when did they go from hydraulic to servomotors? And what year model would be about the oldest that you would recommend for this, I mean to avoid having to rebuild the whole machine completely at astronomical costs or years of work.
>
>

You can't buy a used machine based on year of manufacture. If you don't
want a complete rebuild, you MUST inspect the machine in person, with
instruments, preferably under power. I took a leap on an old lathe, and
ended up with a 22 month rebuild. I am not sorry I did it, but it was a LOT
of work. I now have a truly FINE lathe, however.

Jon