VFD for precision control on a spindle
VFD for precision control on a spindle
(OP)
Hi
New to the forum and have browsed about but did not find a concrete answer for my question.
I would like to be able to use a VFD to maintain a constant speed on a lathe spindle to cut threads with a cnc driven leadscrew.
If its possible, what type of VFD do I need (open loop, closed loop, sensorless vector, v/hz, etc...) and would it REQUIRE a specific motor with some sort of output to the VFD or would a standard 230v 3 phase do ok?
The machine is small and would use about a 1/4 hp motor.
Thanks in advance!
Darren
New to the forum and have browsed about but did not find a concrete answer for my question.
I would like to be able to use a VFD to maintain a constant speed on a lathe spindle to cut threads with a cnc driven leadscrew.
If its possible, what type of VFD do I need (open loop, closed loop, sensorless vector, v/hz, etc...) and would it REQUIRE a specific motor with some sort of output to the VFD or would a standard 230v 3 phase do ok?
The machine is small and would use about a 1/4 hp motor.
Thanks in advance!
Darren





RE: VFD for precision control on a spindle
You would likely want a sensorless vector drive as that will work down to a slow speed (often not zero!). But will also be able to detect a stopped motor whereas a standard scalar drive probably won't.
Oh wait a minute.... you want to cut threads! This means you need accurate angular positioning as you may need to make multiple passes. I think you will need closed loop vector and an encoder instead.
How will you synchronize the cutter to the angle?
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD for precision control on a spindle
I have a 1/4 hp 230v 3 phase 1725 rpm on hand. As far as multiple passes - just one is all need. If I can spin the part at a set RPM and it not drop speed as I apply a "load" I can simply calculate the speed needed for spin in relation to the distance my cut tool travels. Thus 1/4" x 20 = 20rpm by 1 inch/min tool travel or any matching ratio to provide 20 threads per inch.
If I read your reply correct, If I used closed loop vector, I could "manually" rotate the chuck (motor) to a position I choose and the drive will "know" where the motor is?
If I choose closed loop vector / encoder, does that indicate a motor with a sensor installed and a feedback circuit?
If I go sensorless vector it seems I could have the motor at speed and just let my stepper drive "move into" my piece and cut.
I may lose some features with sensorless vector but I am not sure I need rotation location features much.
Is there much cost difference between the two?
I have seen a few affordable 120v in / 230v out drives in the 1hp range but I do not recall any closed loop encoded ones. I do recall another style IBGT, but I think its much like the sensorless vector style.
Oh one last thought, it is ok to oversize the drive (a 1hp to run a 1/4hp motor) correct?
Thanks
Darren
RE: VFD for precision control on a spindle
Thanks for the fast reply.
### You bet!
I have a 1/4 hp 230v 3 phase 1725 rpm on hand.
### Excellent! Hassle averted.
As far as multiple passes - just one is all need.
### Great! Not what I've seen on those insane YouTube machining center demos.
If I can spin the part at a set RPM and it not drop speed as I apply a "load" I can simply calculate the speed needed for spin in relation to the distance my cut tool travels. Thus 1/4" x 20 = 20rpm by 1 inch/min tool travel or any matching ratio to provide 20 threads per inch.
### Fine . Sounds like you have it figured.
If I read your reply correct, If I used closed loop vector, I could "manually" rotate the chuck (motor) to a position I choose and the drive will "know" where the motor is?
### On a fully closed loop setup - yes.
If I choose closed loop vector / encoder, does that indicate a motor with a sensor installed and a feedback circuit?
### Yes.
If I go sensorless vector it seems I could have the motor at speed and just let my stepper drive "move into" my piece and cut.
### Yes this IS what I would do in your 'one pass' case.
I may lose some features with sensorless vector but I am not sure I need rotation location features much.
### You might consider using a drive that can do both. Go with the sensorless mode. If later you need full blown closed loop you drop some money into the encoder and change your VFD's operating mode.
Is there much cost difference between the two?
### The encoders are NOT cheap. Not much price difference on a small VFD like you need. It would be easy to see the encoder cost more than the VFD.
I have seen a few affordable 120v in / 230v out drives in the 1hp range but I do not recall any closed loop encoded ones.
### Keep looking.
I do recall another style IBGT, but I think its much like the sensorless vector style.
### No IBGT is inside the drive and has no bearing on this discussion. Forget you ever heard it. No consequence. (for your application) Marketing gibberish.
Oh one last thought, it is ok to oversize the drive (a 1hp to run a 1/4hp motor) correct?
### Yes within limits. There are some setting inside a drive whose limits you may run up against if you go too far.
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD for precision control on a spindle
Excellent info.
I have seen a couple motors with what appear to be "din" plugs on them. Is this the encoder "built in" to a motor?
I will look for an affordable closed loop version. Any hints are appreciated ;)
Thanks!
darren
RE: VFD for precision control on a spindle
http:/
and about halfway down the page for the encoder modules
ht
Regarding the DIN plugs on motors, there's a fair chance they could be servo motors or spindle drives. Beautifully made and great if you have the hardware to drive them but not often compatible with a commodity drive. Check the nameplate carefully before you buy one.
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If we learn from our mistakes I'm getting a great education!
RE: VFD for precision control on a spindle
That is a pricey little drive but sure does have expansion capabilities. I will have to do some research and see if its cost is worth it for my application. I may go with a cheap sensor less vector (~ $100 - $120 US) to start with and hope prices drop as I may want to upgrade my motor HP or go to one of those servo or spindle drives you mentioned in a couple years.
Thanks!
Darren
RE: VFD for precision control on a spindle
http://
1/3 HP Baldor Motor with provision for encoder mounting (you won't pay the list price)
http://w
RE: VFD for precision control on a spindle
I will research and see what I can locate.
Thanks!
Darren
RE: VFD for precision control on a spindle
I don't see any spec's on how precise you need to be with your speed regulation. Based on the size of the motor you need and the required speed accuracy, you are probably better off with a servo system, as Sreid says.
If you need very high accuracy speed regulation, Danaher Motion Dover has a really accurate spindle velocity controller for servo motors called the DMM-101. It's typically used for air bearing spindles so it may be way overkill for what you need but it may work for standard servo motors as well.
http://www.dovermotion.com/