sizing servos for a cnc lathe

I have decided to abandon trying to reuse the existing dc servos on my Cincinnati lathe, they don't appear to work like any drive I have any understanding of, there is little to no documentation and they are inefficient DC drives with questionable operating characteristics. 

currently the DC drives on the machine are sized at 

5hp X 

7.5hp Z 

30hp on the spindle. with a max rpm of around 1500 rpm iirc. 

amd I right in thinking I can half size these with AC servos running 2x the speed ?

2.5 hp x 

3.75hp Z 

15hp spindle 

 

I don't need 30hp, and i am ok with reducing power. Option b is replacement dc brushed drives, and obviously they'd need to be correctly sized, so meh. 

I'm open to replacing the drives and keeping the motors, but is the financially sensible ??

But can i use a big induction motor like a dc servo ?? I need to be able to orient the spindle, hold it, cut splines etc.  It's got a very difficult to control reliance v*s drive in it now.

Are there any big dc brysged servi controllers out there ?? Outside of this old junk

The issue is that there is zero documentation, and they operate at non standard voltages. The enable circuits also don't work at all like the schematics call out. To top it off they are using a some kind of bizzare constant current output on one leg with a balancing transformer to control direction, this uses a lot of power at idle for little gain. Also the dc motor on the spindle, that reliance drive doesn't seem to have the capability to do things like splines etc. I'm not really sure it can control a motor at sich low speeds. The documen8 I've found indicate that it isn't a very precise control system.

I'd be ok retrofitting to a newer but used servo drive, i just don't know what to shop for.


The issue os that i am involved with a electric/gas bicycle parts start up, the supplier previous used has gone mia and currently we are milling parts at a huge 10x time penalty. So need to get this lathe operational. I purchased it to help this startup and do some ither dtuff like make obsolete auto parts etc.

I have 60kw of 3 phase power on site, but if i ciuld reduce the power consumption of this lsthe id5 be happy about it

The oem chose these motors in 1979 because the industry didn't really have a lot of other proven industrial control solutions.

I put out a email to few suppliers over in chinaville, and i did find a replacement drive.

The lathe belongs nto me BTW, the bike parts startup is just a small business customer I've been serving for a good while now. Ready to grow however.

But I've been trying to find info on dc brushed setvo drives and it's not really out there

Electrokraft i am familiar with. But these Cincinnati servo drives are just, they are weird.

I post the schematics see what you guys think but i suspect the entire machine was designed around these drives

Edit, later units used kollmorgen dc drives, I think this looks like a very affordable way to upgrade and these are welll documented and available in reasonable quantities 

smc.collins wrote:

But can i use a big induction motor like a dc servo ?? I need to be able to orient the spindle, hold it, cut splines etc.  It's got a very difficult to control reliance v*s drive in it now.

Are there any big dc brysged servi controllers out there ?? Outside of this old junk
 

Are you sure the spindle motor is used for positioning?  Not trying to be insulting - I haven't seen your lathe - but an XZC-axis lathe using the main spindle motor for positioniing is unusual.  Not unheard-of, but odd, unless the spindle motor is an AC or DC servo.

The more common approach is to have an induction motor or PMSM driving the spindle through a belt, and a second positioning motor that gets activated during C-axis moves.  Activation can be a belt & clutch or bull gear on the sindle and a servo that pivots in and engages when needed.

This gives the best of both worlds - spindle motor can get geared properly for a reasonable top speed (4kRPM?), and the 'pony' C-axis servo can have a pretty high reduction for very fine positioning and lots of torque with a smallish motor.

This approach flies out the door on swiss-types or lathes with integral-motor spindles.  But I'd think an old Cincy would have a more standard config.