Spindle power by servo motor

[Stevie]

Hi guys
I am thinking of powering the small lathe I've built with a brush or brushless servo; I've seen many go through eBay at good prices
My question is would it have enough power at low rpm; if I was to go with a drive/servo setup of about 1/2hp
Can a program like Artsoft or Turbo be used to just spin the spindle at high rpm's
I am thinking if this is possible then indexing the spindle would be possible (I think) I could then add 2 more slides over the main spindle and be able to cut like a rotary table (or dividing head)
My goal is to cut the whole 25mm antiaircraft gun barrel in 1 setup (1/48th scale) I need about 156 of them

Or the second option is a stepper drive that would replace the drive motor for the indexing; lot of messing around; the 1st option would be best "IF it's possible"

I ask the experts

[HuFlungDung]

Stevie,

If its a real small lathe, and a large servo motor, it might work okay. The only reservation on the subject is that if you ever start turning larger diameters on your lathe, then you will have to slow the spindle considerably, in order to not overheat your tools. Combine that with the fact that when working on the outer diameter of a larger part, that the torque required to turn the part is greater than at the small diameter. This is simple leverage working against you, rather than for you.

"Real" cnc lathes use a servo drive of some sort. CNC lathes typically have a huge motor, for the very same reasons as I outlined above. Most of them will have two or more gear ranges, too, to get the motor operating in the proper torque/speed range.

I have a 20hp cnc lathe, 20inch swing. When turning steel at say a 12" diameter, the motor is running very slowly, and the machine is practically useless, because the depths of cut must be very shallow. Yet in turning aluminum at that diameter, the machine is good, because I can get the rpms up to where the motor has much better torque.

That said, you might still need some kind of range gears or belt drives on your machine. Depending on your controller software, you might have to look into the complexity of redefining the spindle drive ratio every time you decide you need to change speed ranges. Preferably, you would not want to have to shut down and go into the controller setup to do this every time this contingency occurred. On the other hand, on any one job, you might never have need to change speed ranges in the middle of the job.

[Stevie]

Hu

The lathe is tiny; max dia 5/8" all collet

I'll only be cutting "none" ferrus; it's for model parts (ships)

I'm using an AC 1/2hp right now and it seems overkill; way more power than this needs

so maybe I could use servo's

[HuFlungDung]

Sounds good then. Go for it

[ESjaavik]

What you would have is constant torque up to one RPM, then constant HP from there on. Greatly simplified of course. I have been thinking the same, mostly because a BLDC servo have a high power/weight ratio if you don't count in the servo drive. But since only the motor is moving around, that's what matters. Don't forget the price of the drive though. It costs as much or more than the motor. Also make sure you can get matching motor and drive. Not always easy at eBay.

If you don't want to use it as a C-axis, you can drive it with a simple frequency generator. It can be built from a 555 for a few dollars.

Don't consider a stepper. It has some nasty resonance bands, and makes a lot of noise when big enough to do what you need.