[jderou]

So my spindle right now is driven by a 7.5hp AC induction motor & VFD. I have it limited to 5k rpm, which I am satisfied with. I would like to convert to a servo driven spindle, but I have not found a servo motor capable of that RPM (directly driven). My question is, how do the big manufacturers do it? I am pretty sure at least some of the 10,000 rpm spindles I have used were direct drive.
What do I need to look for to find a motor capable of 5000 rpm and still have decent hp? I don't need 7.5. 2 or 3 would likely be enough.
I have a 3.5hp servo with a max of 3000 rpm. If I put a 2:1 pulley on it I will have the rpm, but will likely not have enough hp.
Suggestions?

[jderou]

Maybe I am better off keeping my current setup and changing my VFD to a vector drive like this:
http://www.ebay.com/itm/HITACHI-WJ20...item1c4f66f7cc
This should give me spindle orient, and the potential to rigid tap, correct?

[mactec54]

jderou

Most likely will get you heading in the right direction,but you need a spindle encoder feed back, to the control, then a control that can synchronize the Z axes with the spindle to do rigid tapping

[Larken]

So my spindle right now is driven by a 7.5hp AC induction motor & VFD. I have it limited to 5k rpm, which I am satisfied with. I would like to convert to a servo driven spindle, but I have not found a servo motor capable of that RPM (directly driven). My question is, how do the big manufacturers do it? I am pretty sure at least some of the 10,000 rpm spindles I have used were direct drive.
What do I need to look for to find a motor capable of 5000 rpm and still have decent hp? I don't need 7.5. 2 or 3 would likely be enough.
I have a 3.5hp servo with a max of 3000 rpm. If I put a 2:1 pulley on it I will have the rpm, but will likely not have enough hp.
Suggestions?

The biggest difference between a standard motor and a Spindle motor is Bearings and balancing. It usually takes precision (expensive) angular thrust bearings to run cool above 6000 rpm.
You could try changing the bearings in a good quality AC 3600rpm motor and have it precision balanced and probably get 4800-6000 rpm running the inverter at 80-100 hz.

On a different note, Its hard to believe that a 1.8L 4 cylinder Honda piston engine with crankshaft, valves, pistons going up and down, and all the moving parts can run at 9000 rpm ... and a electric motor can't , wow !

Larry K

[jderou]

Larry,
I am already pushing the limits of my AC motor . I should be maxed out at 3600, but I have been running it at 5000 for some time now. Seems to be fairly well balanced. I actually had it up to 7000 once briefly, that was pushing it way too far.
Interesting point about the 4 cylinder though, heck sportbikes are up 16,000+ rpm!
I am thinking it makes more sense for my application to go with the vector drive. I may be able to sell my big servo and drive and get enough to buy the hitachi vfd.

[underthetire]

Cause the big boys charge lots of money
10K and higher are available, its just really pricey. Yaskawa has some for open architecture. Fanuc is also a big player, but your pretty much stuck with using there controls.

[Larken]

You can also get a 12000 rpm (not 18K or 24K) Perske or Colombo for lower speed cutting. We had a 6Hp 12000 rpm one on a big machine we made.
The make Granite cutting spindles too that may do the job.

Larry