which do you prefer a Lathe or bench top drill/mill

[Ultrashovel]

VFDs are quite popular but will only work on one machine each. They do give convenient speed changes but having a separate unit for each machine can add up. Also, VFD's for larger hp usage are rather expensive.

I have a friend with one VFD connected to his Bridgeport mill and his Grizzly lathe. He has a switch running a couple contactors so he can switch the output between the two machines. The only caution is he has to be careful not to switch the contactors with the VFD output running. He has been running this set up for maybe ten years.

I can see how that would work. The hp requirements for each machine would have to be very close to one another to prevent issues.

[PoorUB]

I can see how that would work. The hp requirements for each machine would have to be very close to one another to prevent issues.

What difference would that make? I am running a 1 HP motor on a 10 HP VFD. The only issue is the motor protection settings will not go low enough to protect the motor. I don't see it as an issue with a machine that runs only while you are standing by It.

[Admiral Akbar]

How much can you vary the frequency of the motor input on a VFD?  Trying to slow the motor down, I would expect that there is not enough internal inductance in the motor to allow more than say 1/2 speed... Even then I'd expect the motor to run hotter and have less TQ output..

Max

[Don D]

I go from 60 to 8rpm but do that no longer than 15 seconds or so. Low torque demand. No issues but I agree torque and heat are affected. If anyone was running high duty cycle an induction rated motor is required and a constant torque vfd. Gets very costly fast.

[Ultrashovel]

I can see how that would work. The hp requirements for each machine would have to be very close to one another to prevent issues.

What difference would that make? I am running a 1 HP motor on a 10 HP VFD. The only issue is the motor protection settings will not go low enough to protect the motor. I don't see it as an issue with a machine that runs only while you are standing by It.

VFDs, as I understand them, have to be programmed for a specific motor. That would include hp and current draw. This is not my opinion. I've heard this discussed many times.

Can you switch a single VFD from one motor load to another? Yes, but you need to re-program  for that specific motor. An example would be changing your VFD from a 2 hp 1,750 rpm motor to a 1 hp 3,600 rpm motor. It would be necessary to reprogram.

[PoorUB]

Ultra, what you have been told is not completely true. I worked with VFD' s for 12 years. You need to program in the output voltage, hertz, and to protect the motor you need to program in the volts and amps of the motor, only if you want the VFD to trip if the motor overloads. The VFD could care less what the motor is. The VFD  just sends out voltage at whatever hertz, and amps depending on the motor load. You could run a1 HP motor on a 100  HP VFD if you wanted.

[Ultrashovel]

Ultra, what you have been told is not completely true. I worked with VFD' s for 12 years. You need to program in the output voltage, hertz, and to protect the motor you need to program in the volts and amps of the motor, only if you want the VFD to trip if the motor overloads. The VFD could care less what the motor is. The VFD  just sends out voltage at whatever hertz, and amps depending on the motor load. You could run a1 HP motor on a 100  HP VFD if you wanted.

There are numerous articles on the Internet regarding setup of VFDs. We are apparently talking about two different issues. It seems, however, that in general you are saying that you can connect any VFD to any motor (smaller than the VFD capability let's say) with no consideration of the programming in the VFD.

From the article link below (just one of many that can be found)

"Common adjustable parameters (on VFDs) include the following:

    Preset speeds
    Minimum & maximum speeds
    Acceleration & deceleration rates
    Two- & three-wire remote control modes
    Stop modes: ramp, coast, DC injection
    Automatic torque boost
    Current limit
    Configurable input jog
    V/Hz settings
    Carrier frequency
    Program password

Variable frequency drives come with factory default settings for most parameters that are more conservative in nature. The default value settings simplify the start-up procedure.

However, parameters for motor nameplate data are not factory-set (unless a matched VFD & motor has been purchased) & must be entered in the field.

http://www.vfds.org/vfd-parameters-programming-setting-102674.html

[PoorUB]

There are numerous articles on the Internet regarding setup of VFDs. We are apparently talking about two different issues. It seems, however, that in general you are saying that you can connect any VFD to any motor (smaller than the VFD capability let's say) with no consideration of the programming in the VFD.

From the article link below (just one of many that can be found)

"Common adjustable parameters (on VFDs) include the following:

    Preset speeds
    Minimum & maximum speeds
    Acceleration & deceleration rates
    Two- & three-wire remote control modes
    Stop modes: ramp, coast, DC injection
    Automatic torque boost
    Current limit
    Configurable input jog
    V/Hz settings
    Carrier frequency
    Program password

Variable frequency drives come with factory default settings for most parameters that are more conservative in nature. The default value settings simplify the start-up procedure.

However, parameters for motor nameplate data are not factory-set (unless a matched VFD & motor has been purchased) & must be entered in the field.

http://www.vfds.org/vfd-parameters-programming-setting-102674.html

Your first statement is pretty much correct. As long as you have the output voltage and speeds set to a reasonable setting you can safely run a motor. The VFD just outputs a certain voltage and Hz, what ever the parameters are on the VFD and will run a small or large motor just fine, under it's rated size. The settings specific to a certain motor are there for the overload protection of the motor. Many times we would need to get and large air conditioning unit running and we would just run through the basic settings, set the VFD to manual control and flip the power switch on. Sometimes it was weeks before we got back to do a proper setup.

The settings you listed are operating parameters and don't have much to do with the specific motor. Generally the specific settings for a motor are voltage, max amps, max RPM and that is about it. The rest of the numerous settings are control settings on how the VFD operates to motor.

That 10 HP VFD running a 1 HP motor on my big drill press works just fine. I can run the motor from 0 Hz to 120 Hz and double the motor output RPM. The drill press came with a 1725 RPM motor so at 120 Hz it is spinning at 3450 RPM. The only short coming is the 10 HP VFD minimum motor protection settings are well about what the 1 HP motor needs for over load protection, but as it is a drill press and the motor runs only while I am running it I don't see and issue. If I stall/overload the motor the VFD will not drop off like it would with a properly sized motor/VFD combination. Also the braking does not work with the miss match in size so i can only set the VFD to coast toaa stop. The VFD does not know what size motor it is running, it just sees a load, in this case well below the minimum it is rated for. As for over heating the motor at low speeds it does not run there very long so again it is not and issue. If the VFD was running a pump or fan motor that ran untended then the motor settings are important.

I worked on VFD's from 3/4 HP up around 50 HP, 208 volts to 480 volts. We installed air handlers with one VFD running up to 12 motors at a time, so the motor settings were multiplied 12 times from the motor name plate. Then to weird things out there were motor over loads between the VFD and motor which is generally a no-no, but with multiple motors it is assumed that they all will not fail at one time so the loss of one or two motors does not affect the operation of  the VFD.

A VFD can be a bitch to program. Some are fairly simple with just a few settings, some have hundreds of pages of settings and if you miss one it will not run. I spent 3 hours programing two VFD's on a rooftop at -20F, no fun when you are freezing to death! I could get the one VFD to run in auto, but not the other. I finally had a coworker come up and we went through pages and pages of settings and compared the settings on the two VFD's until we found the one parameter that I missed.

[Admiral Akbar]

I can run the motor from 0 Hz to 120 Hz and double the motor output RPM.

So ou can run the motor on 1 hz frequency and get about 29 rpm?

Cool but I doubt it...

Max

[Ultrashovel]

I can run the motor from 0 Hz to 120 Hz and double the motor output RPM.

So ou can run the motor on 1 hz frequency and get about 29 rpm?

Cool but I doubt it...

Max

Yes its true in theory that the lower the frequency provided to a 3 phase motor, the slower it will go. I would never want to go that slow, though. The problem with running a motor too slow, especially when using a mill, it that the motors often are TECF (Totally Enclosed w/Cooling Fan). Prolonged running at extreme low frequencies will also slow down the fan and therefore the motor will tend to heat up. There is a loss of torque at extreme low speeds as well. People with belt-change Bridgeports often set the belt at a low speed and that keeps the rpm's up so at to prevent heating.

Additionally, a very old motor perhaps one with poor or cracked internal wires, won't work too well with a VFD. They may tend to overheat at low frequencies.
In my case, most of my work is done at 1,000 rpm with changes to the back gear which automatically give me slower speeds. I do have to change speeds for power tapping, but that's not all that often.

With all of this said, there are many advantages to a VFD where production work on a mill or lathe requires frequent speed changes. They are very reliable these days and have many more features including braking, slow ramp up and down and good protection built in. As I have said before, these features need to be tailored to each motor when the VFD is initially installed.

I'm going to stick with my home made rotary phase converter for a while longer, though.

Happy Trails to all.

[PoorUB]

I can run the motor from 0 Hz to 120 Hz and double the motor output RPM.

So ou can run the motor on 1 hz frequency and get about 29 rpm?

Cool but I doubt it...

Max

I guess I am not really sure what the bottom end of the motor RPM is, but I know the spindle speed with the belt reduction is pretty slow, maybe 60 RPM at the motor. I suppose I can video it and share it is anyone cares. I know it will go to 0 RPM! Just not sure what the practical lower RPM is. I do know when I first set the VFD up on the drill press I ran the variable belt drive to the lowest speed, and the VFD to the lowest setting where it would still maintain RPM and I grabbed the drill chuck with a 14" Channel Lock pliers and I could not stall the spindle so there is still pretty good torque at the bottom end.

I took a few minutes and ran out to the garage to look at my drill press. Also the motor is a 1150 RPM, not a 1725 RPM. The read out on the VFD was 5, I set it up to show Hz so the motor was running at 5 Hz or 95 RPM at a stable RPM. If I grabbed the chuck with a pliers with the belt reduction at the slowest speed I could not stop the motor, about a 9to1 reduction, so about 10 RPM at the chuck. I could get the motor to run at 3 HZ, but not reliably, and no torque at the chuck, I could stall it easily.

[Admiral Akbar]

I can run the motor from 0 Hz to 120 Hz and double the motor output RPM.

So ou can run the motor on 1 hz frequency and get about 29 rpm?

Cool but I doubt it...

Max

I guess I am not really sure what the bottom end of the motor RPM is, but I know the spindle speed with the belt reduction is pretty slow, maybe 60 RPM at the motor. I suppose I can video it and share it is anyone cares. I know it will go to 0 RPM! Just not sure what the practical lower RPM is. I do know when I first set the VFD up on the drill press I ran the variable belt drive to the lowest speed, and the VFD to the lowest setting where it would still maintain RPM and I grabbed the drill chuck with a 14" Channel Lock pliers and I could not stall the spindle so there is still pretty good torque at the bottom end.

I took a few minutes and ran out to the garage to look at my drill press. Also the motor is a 1150 RPM, not a 1725 RPM. The read out on the VFD was 5, I set it up to show Hz so the motor was running at 5 Hz or 95 RPM at a stable RPM. If I grabbed the chuck with a pliers with the belt reduction at the slowest speed I could not stop the motor, about a 9to1 reduction, so about 10 RPM at the chuck. I could get the motor to run at 3 HZ, but not reliably, and no torque at the chuck, I could stall it easily.

If you can run it at say 3 hz that pretty much means the motor is no longer driven by say 220 volts.. The VFD becomes a current source and no longer a voltage source.. Current is what makes the magnetic field the drives the motor anyway..

Max

[Don D]

You loose HP, proportional to the frequency drop, as the frequency drops below 60hz and the torque remains constant. Overdriving or underdriving the motor can cause heat issues. That is why they have the TEFC motors that are induction rated. Overdriving does not provide additional HP and torque begins to decline.Correct Max?

[Admiral Akbar]

You loose HP, proportional to the frequency drop, as the frequency drops below 60hz and the torque remains constant. Overdriving or underdriving the motor can cause heat issues. That is why they have the TEFC motors that are induction rated. Overdriving does not provide additional HP and torque begins to decline.Correct Max?

Sounds good too me.. I'm just learning here as all the applications I ever worked on were either constant speed induction, synchros (form a variable speed 3 phase motor) and steppers..  The Synchros is close but the armature field was powered so they typically used constant frequency AC.. (IIRC),

Max

[ALUCARD19]

Find a used Bridgeport mill you will be able to mill, drill, bore, just make sure you get one with an electric table feed, also a + is a digital readout.
You will also need dial calipers, micrometers, bore gauges, indicators, and a granite surface plate would also be good, then you need mills, drills, R8 collets (set), boring head and boring bar, cylinder hones, fly cutter.
Look at $7,500.00 to $10,000 to set yourself up for doing heads and other machining.
I was a tool/die maker for 25 years and did all sorts of milling, grinding. All it takes is money, I have all the tools except milling machine will sell to you for $15,000 rolling toolbox included.