sizing servos for a cnc lathe

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

My Spidey-Sense says "Run Away"

Or, at the very least, make it very clear what is "not my fault"

The OEM chose these motors for good reasons, based on what the lathe was expected to do,

You could certainly wind it back, a 3HP lathe can make the same parts as a 30hp lathe. My own lathe is 3hp and it's great,

If it make parts then your "customers" probably won't spot that it makes 4 parts per hour rather than 100.

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.

 

I need the spindle to be used as a C axis, I plan to add live tooling in the near future. It is a DC servo however. It is a slant bed lathe with a 6 station turret with 2 rings of tools. I will be doing some measuring work tomorrow, my spindle also has a brake on it, handy for such endeavors as cutting splines, live tool milling etc. 

I think the newer DC drives on the existing servo motors is the best way forward. obviously this will require me to verify the electrical specifications of the dc servo motors, but pretty much any brushed DC motor can be a servo with sufficient cogging and a encoder. 

Sounds ambitious but should be pretty sweet when you get it sorted out.

FYI - there's a good thread under the "Turning" category where a member built a C-axis lathe from scratch.  I believe he managed to work out some of the issues surrounding switching between turning mode and C-axis mode for polar interpolation milling.  Might want to have a look.